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PRESSURE IN THE EARLY LIFE HISTORY
OF SOCKEYE SALMON
by
HAROLD HENRY HARVEY
B.Sc. University of Manitoba, 1953
M.Sc. University of Manitoba, 1956
MILO C. B"RLL
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A THESIS SUBMITTED IN''PARTIAL FULFILMENT OF
THE REQUIREMENTS OF THE DEGREE OF
DOCTOR OF PHILOSOPHY
in the
DEPARTMENT OF ZOOLOGY
We accept this thesis as conforming to the
standard required from candidates for the
?-egree of DOCTOR OF PHILOSOPHY
Members of the Department of Zoology
The University of British Columbia
August , 1963
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ABSTRACT ,__ _ __:
Young sockeye salmon (Oncorhynchus nerka) may occupy
the epilimnion, thermocline or hypolimnion during lacustrine
residence and may make extensive vertical migrations. Resi-
dence and migration over a range of pressure presents fish
with certain physiological problems. Sockeye salmon meet
these problems by adaptation, compromise and fortuity.
Sockeye evidenced a tolerance to pressure in excess of ZO
atmospheres, equivalent to a depth of water of 680 feet.
Sockeye fry showed no behavioral I!esponse to pressure prior
to initial filling of the swim bladder, but thereafter pressure
induced compensatory swimming. Young sockeye proved to be r
dependent on atmospheric air for inflation of the swim bladder.
The restrictions to vertical movement imposed by the swim-
bladder are minimized in sockeye by a relatively small bladder
volume, little excess pressure within the bladder, the bladder
being thin-walled and extensible and the inability of these fish
to secrete gas into the bladder. When frightened, young
sockeye sounded and expelled gas from the swim bladder. Gas
expulsion was found to be under adrenergic control and
retention of gas in the swimbladder under cholinergic control.
During decompression with upward movement through therm-
ally stratified water, gas disease or the "bends" is obviated
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by the rapid clearance of dissolved nitrogen from the blood
stream. Young sockeye showed a tolerance to rapid decom-
pression except under conditions permitting swimbladder gas
.td' appear as emboli in the blood stream.
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ACKNO"'i.NLEDGMENTS
The author wishes to express a deep-felt gratitude
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to Dr. w.s. Hoar through whose inspiration and patient I
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direction this work was conducted. The author is indebted
to Dr. P.A. Larkin for advice on statistical problems.
The manuscript was examined cirtically by Dr. D. H. Copp,
Dr. B. McK. Bary and Dr. P.A. Larkin to whom the -l
author expresses his appreciation.
The pressure chamber was designed by Mr. J. Pyper,
engineer, of the International Pacific Salmon Fisheries
Commission. Technical assistance was required in the oper-
r
ation of the equipment and this was ably offered by Mr.
L. W. Johnston and Mr. E. Stone. The author is indebted
to Miss E. Haskell and Mr o Johnston for assistance with
the illustrations.
Thanks are due to Dr. F.R.H. Jones, whose incred-
ulity in no small measure contributed to the ext;ent to which
the work was pursued. Thanks are due a~o to Mr. J.
Terpenning for the use of facilities and fish at the Cultus
Lake Trout Hatchery.
This study was supported financially by the International
Pacific Salmon Fisheries Commission o For this support the
author is deeply grateful.
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In presenting this thesis in partial fulfilment of the
requirements for an advanced degree at the University of
British Columbia, I agree that the library shall make it
freely available for reference and study. I further agree
that permission for extensive copying of this thesis for
scholarly purposes may be granted by the Head of my
department or by his representatives. It is understood
that copying or publication of this thesis for financial gain
shall not be allowed without my '(Vritten permission.
.,
Department of Zoology
The University of British Columbia
Vancouver 8, Canada
Date
TABLE OF CONTENTS
CHAPTER PAGE
I. INTRODUCTION . . . 1
II. METHODS 0 0 g 0 0 0 0 0 0 0 • 0 0 0 0 0 4
General 0 0 0 0 Q 0 0 0 0 0 0 0 0 0 • 0 4
Pressure in Relation to Behavior 0 • 11
Pressure in Relation to Swimbladder • 0 • 15
Measurements on the fish • 0 0 0 0 15
Determination of volume . . 0 0 • 0 • 16
Determination of weight • • 0 • 0 • 0 16
Determination of density • 0 0 0 0 0 0 17
Measurements on the swim bladder. 19 I
I
Volume of the bladder • 0 • • 0 0 19
Ambient pressure 0 0 0 0 0 0 0 0 0 0 23
Extensibility of the bladder • • • • 0 26
Contractibility of the bladder . . 30
Gas secretion • 0 • • • 0 • • • 0 • 33
Measurements on the pneumatic duct 38
Loss of gas on sounding • • 38
Gulping atmospheric air 42
Duct-release pressure • • . . . 0 • • 46
Histological examination • • • • 0 50
(,) Pressure in Relation to Gases • • • • . . 50
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CHAPTER
vii
PAGE
L imnological investigations • 0 0 0 • • • 0 51
Site of study 0 0 0 0 . • 51
Measurement of temperature 0 • • • 0 52
Measurement of dissolved gases . . • 0 52
Calculations • 0 0 0 0 0 0 • 0 0 • • 0 0 53
Measurement of tolerance to pressure • • 53
Magnitude of positive and negative
pressure • 0 0 0 0 • • • 0 0 • • • • 54
Duration of positive and negative
pressure ·,
• 0 • 0 • • • 55 • • • • • 0 0
Rate of increase and decrease in
'pressure 0 0 0 • 0 • 0 0 • 0 0 0 56
Conditions altering resistance to decem-
pression 0 • • • 0 0 0 0 • 56
Seasonal effect • 0 • . . . . . • 0 • 0 56
Holding smelts at lake surface and depth 58
Increasing content of dissolved gases 0 • 59
Changes in temperature . . • 0 • 0 •• 62
Swim bladder gas in relation to pressure •• 63
Increasing and decreasing gas content
of the bladder • • • • • • • • • • • • 63
Bladderless and catheterized-bladder fish 65
Duct-release pressure and holding sock-
eye at depth . . . . . • • • • • • • 67
viii
CHAPTER PAGE
Equilibration of fish with dissolved nitro-
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. gen of environment • • • • • 0 0 0 • 0 67
Rate of change of nitrogen in venous
and arterial blood • • • 0 • 0 0 • • • 68
Rate of equilibration of total dissolved
nitrogen 0 . 0 0 0 0 0 0 0 0 0 0 0 0 69
III. RESULTS • 0 • 0 0 0 . •o • • • 0 0 0 0 0 0 72
Pressure in Relation to Behavior 0 0 . 0 0 72 -I
Response of one-year-old smots 0 0 • 0 • 72
Response of fry and fingerlings • • • • • 76 -l
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Response of yearlings and two-year-old
smolts • • • • • 0 • • • • • • • • 0 • 78 J
Pressure in Relation to Swim bladder • • • • 78
Volume of the bladder 0 • • . • . • 0 0 . 78
Ambient pressure • 0 • • • • • • • • • • 80
Extensibility of the bladder . . . . . . . 80 -l
Contractibility of the bladder . . . . . .
Gas secretion • . . . . . . . • • . . • • 83
Loss of gas on sounding • • • . . . . • • 83
Gulping atmospheric air . . . . . . . . . 89
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Duct-release pressure • • • • • • . . . . 90
Histological examination • • • • • 0 • • • 92
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CHAPTER
Pressure in Relation to Gases • • • • • •
Limnological investigations • • • • • • •
-·---·----
Temperature . . . . . . . . . . . .
Oxygen content and saturation •
Nitrogen content and saturation . . .
Tolerance to pressure and resistance to
decompression • • • • • • • • •
Magnitude of positive and negative
pressure • • • • • • • • • • •
Duration of positive and negative
• •
pressure • • • • • • • • • • • • •
Rate of increase and decrease in
pressure • • • • • • • • • • • • •
Conditions altering resistance to decom-
pression • • • • • • • • • • • • • •
Season~ effect • • • • • • • • • • •
Smolts held at lake surface and depth
Increased content of dissolved gases •
Changes ~ temperature . . . . . . .
Swimbladder gas and resistance to de-
compression • • • • • • • • • • •
Increased and decreased gas content
of the bladder • • • • • • • • • • •
ix
PAGE
92
92
94
108
109
113
113
114
115
119
119
121
122
126
129
129
CHAPTER
Bladderless and catheterized-bladder
fish • 0 • • 0 0 • • • • 0 0 0 0 •
Duct-release pressure and sockeye
held at depth 0 0 0 • • • 0 0 • 0 •
Equilibration of fish with dissolved nitro-
gen of the environment. • • • • 0 0 0
Rate of change of nitrogen in venous
blood • • • • • 0 • • • • • • • • •
Rate of equilibration of total dissolved
oxygen • • • • • • • • • • • • • •
IV. DISCUSSION • 0 • • • • • • • • • • • •
The problem of pressure stimulating alevins
and fry • • • 0 • 0 0 0 • • • • • 0 0 •
The problem of maintaining preferred
depth • • 0 0 • 0 • • • • • • • •
The problem of maintaining buoyancy . . .
The problem of restrictions imposed by
the swimbladder 0 • • • • • • • •
The problem of escape from predators
The problem of gas disease in sockeye
during vertical migrations in stratified
lakes . . . . . . . . . . . . . . . .
X
PAGE
130
130
131
131
131
135
135
137
144
147
150
152
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CHAPTER
The problem of tolerance to pressure and
resistance to decompression • • • 0 0 8
The problem of the temperature barrier
to the downstream migration of sockeye
smelts 8 • • 0 0 0 0 0 • • 0 • • • • •
v. SUMMARY AND CONCLUSIONS • • • 0 •
Summary 0 0 0 • 0 • • • • • • • ~ 0
Conclusions 8 0 0 D 0 0 0 0 • • • • 0 . .
VI. REVIEW OF RELATED LITERATURE
Pressure Perception and Response in Fish
Pressure and gas secretion . . . . . .
Decompression and gas resorption . . .
Pressure and air gulping in physostomes.
Decompression and gas emission in
physostomes . . . . . . . . . . . .
Anatomical basis of perception of
pressure • • • • • • • • • • • • • •
Neurophysiological studies . . . . . . .
Response to changes in barometric
pressure • • • • • • • • • • • •
Pressure and compensatory swimming • •
Pressure conditioning of fish . . .
The Effects on Fish of Positive and
Negative Pressures . . . . . . . . . .
xi
PAGE
155
156
162
162
165
167
167
167
174
177
181
188
190
192
198
203
205
xii
CHAPTER PAGE
The effects of positive pressure • • . . 205
The effects of negative pressure o o 0 0 208
The effects of cyclical changes in
pressure o o • o o o • • • • o • • • 215
LITERATURE CITED •• 0 0 0 0 0 0 0 0 0 0 223
APPENDIX A. Theoretical Considerations • 0 0 0 241
APPENDIX B. Methods of Gas Analysis 0 0 257
LIST OF TABLES
TABLE PAGE
I. Increase in oxygen. and nitrogen saturation
during aeration under pressure • • 0 0 61
l II o Temperature in degrees Fahrenheit of Cultus
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Lake, 1961 • 0 0 0 0 0 0 • 0 • • 0 • 0 • 95
III. Dissolved oxygen in milligrams per liter of
Cultus Lake, 1961 0 0 • • • • • • . • . 98
:IV. Oxygen expressed as per cent of air satur-
ation . 0 0 0 0 • • 0 • • . • . • . . • . 100
v. Oxygen expresf:led as per cent of air satur-
ation at surface temperature 0 0 D 0 104
VI. Dissolved nitrogen content, per cent of air
saturation and per cent of air saturation
at surface temperature • • • • • • 0 0 0 107
VII. Water vapor pressure in mm Hg for temper-
J atures of 0 to 100 degrees Cent~rade • 0 247
' VIIL Solubility of oxygen in ml per liter • • • 0 • 249
1 ',, IX. Solubility of oxygen in mg per liter • • • • • 251
I
l Xo Solubility of nitrogen in ml per liter 253
XI. Solubility of nitrogen in mg per liter . . . . 255
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LIST OF FIGURES
FIGURE PAGE
1. Cultus Lake 9 British Columbia, site of the
investigation of pressure in the life. history
of the sockeye g Q 0 0 0 • • • • 8 0 0 • 6
2. Daily migration of sockeye smolts from Cultus
Lake during two years of the study 0 0 0 7
3 o Pressure chamber located close to the weir
on Sweitzer Creek 0 • 0 0 • • 0 0 0 0 0 8
4o Diagrammatic representation of pressure
apparatus o 0 0 0 0 0 0 0 0 • • • • • • 0 9
5. Characteristic posture of sockeye salmon
smolts at atmospheric pressure and at a
pressure of 50 psi above atmospheric o 0 0 12
6 o Posture and rate of pectoral fins of a smolt
at pressures above and below atmospheric o 13
7 o Apparatus for the measurement of ambient
pressure within the swimbladder • 0 0 24
8 o Calculation of excess pressure within the
swim bladder 0 0 0 0 0 0 • • 0 0 0 0 • 27
9. Apparatus for the measurement of the pres-
sure required to force gas out through the
pneumatic duct 0 0 0 0 • 0 • • • 0 • 0 0 28
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FIGURE
10. Investigation of inflation of the swim bladder
with and without access to atmospheric air
11. Smelt density and magnitude of vacuum neces-
sary to affect neutral buoyancy e o o o o o
12. ~pparatus used to induce the sounding res-
ponse in sockeye smelts • • • 0 0 0 0 0 • •
13. Response to sockeye smelts with a catheter-
ized swim bladder 0 0 0 0 • • • 0 • 0 0 0 0
14. Calculation of pneumatic duct-release pressure
from theoretical and observed expansion of
the swim bladder up to time of gas es:eape,. •
15. Change of temperature internally of fish
transferred from 45 to 60° F water 0 0 • •
16. ~verage and range of pectoral fin beats for
ten sockeye smelts from atmospheric pres-
sure to 250 psi above atmospheric 0 • 0 0 •
17. ~verage pectoral fin rates of fry and three-,
six-and nine-month fingerlings • • o • • • •
18. ~verage pectoral fin rates of eighteen-month
and two-year-old sockeye . . . . • 0 •
Density of sockeye smelts held above and
below screens 0 • 0 • • • • • • • • 0
XV
P~GE
34
37
40
45
47
64
73
77
79
84
xvi
FIGURE PAGE
20. Density of sockeye smelts on sounding.
Test fish exposed to 100 mg per liter
of ephedrine for up to 12 hours 0 0 0 86
21. Density of sockeye smelts on sounding.
Test fish exposed to 5 mg per liter
of 11 dibenzyline" 0 0 0 0 0 0 • • 0 0 0 0 0 88
22. Change in pressure required to force gas
out through the pneumatic duct following
the death of the animal 0 0 0 0 0 0 0 • 0 91
23 o Photomicrographs of the pneumatic duct of
the sockeye smelt 0 0 0 • • • • • • • 0 93
24. Temperature of the upper 50 feet of Cultus
Lake during 1961 o o ·o o o • o e • o o o 97
25. Dissolved oxygen content in milligrams per
liter, Cultus Lake, 1961 • • • • • 0 • • 102
26o Oxygen content expressed as per cent of air
saturation at surface pressure and temper-
a ture in situ • 0 0 • 0 • • • • • • • 0 • 103
27. Oxygen expressed as per cent of air satur-
ation at surface pressure and temperature 106
28. Dissolved nitrogen content in milligrams per
liter, Cultus Lake, 1961 0 • • • 0 0 • • 110
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FIGURE
29o · Nttrogen content expressed as per cent of
air saturation at surface pressure and
temperature ~ situ o • • • • • • • • o •
30 o Nitrogen expressed as per cent of air satur-
ation at surface temperature and pressure
31. Mortality per week following decompression
from 50 psi to positive and negative
pressures • • • • o o o o o • • • • o • o
32 o Mortality per week following decompression
from 300 psi to positive and negative
pressures • o o • • • • • • • • • • • • •
33. Mortality per week accompa:nying various
rates of reduction of pressure • 0 0 • 0 •
34. Mortality of sockeye smelts tested at var-
ious temperatures during the course of
the migration, 1959 0 0 0 • • • • • • • •
35 o Decline in mortality among groups of smelts
held up to 72 hours in Sweitzer Creek
before testing • 0 0 • • • • • • • • • •
36 o Mortality among smelts accompanying residence
in surface and thermocline waters • 0 • 0
37. Mortality among _smelts following exposure to
water of increased air content • • • • • •
xvii
PAGE
111
112
116
117
118
120
123
124
125
xviii
FIGURE PAGE
38. Mortality on decompression following sudden
increase in temperature • • 0 • • • • • • 127
39. Temperature increases expressed as increases
in per cent saturation • • • . . . • 0 0 0 128
40. Decrease in nitrogen in venous blood
following transfer of fish from water of
17. 5 ml per liteh·, nitrogen to 13 • 0 ml per
liter • • • • • • 0 Cl ... • • • • • • • • • 132
41. Per cent of excess nitrogen retained by fish
following transfer from water of 14.4 to
1. 6 ml per liter nitrogen • • • • • • • • 133
42. Change in unit v;olume of gas in relation to
depth and pressure • • • • • • • • • • •
43. Change in the density of a sockeye smelt
with increasing depth and pressure • • . . 140
44. Pectoral fin beats in relation to sockeye
smelt density • • • • • • • • • • • • • • 141
45. The effect of sounding on pressure-induced
change in density . . . . . . . . . . . . 142
46. Per cent saturation in relation to pressure
and depth • • • • • . . . . . . . . 243
4 7. Oxygen and nitrogen content of air-equilibra-
( ted water, 0 to 30°C . . . . . . . . . 244 L
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CHAPTER I
INTRODUCTION
The sockeye P Oncorhynchus nerka, in se:veral respects
is unique among the Pacific salmon. The adult fish typically
spawn in streams flowing into lakes but may utilize outlet
streams or the bottom of the lake itself. The eggs are
deposited in the autumn within a nest or redd in the stream
gravel, hatch during the winter and emerge from the gravel
as fry in the spring. The fry most commonly are carried
downstream into a lake, but may swim upstream if spawned
----in the outlet; or if spawned on the lake bottom P ·they stay
within the lake. Within the Fraser River system, young sock-
eye usually remain one year in lake residence; occasionally
they will remain two years but rarely zero or three years.
Typically sockeye migrate from the lake environment in the
spring of the year at a length of perhaps three inches. On
leaving fresh water, the young sockeye enter the ocean and
remain there generally two but occasionally one or three years.
The adult fish return to fresh water late in their third
year, spawning four years ·after having been deposited in the
gravel.
The period of lake residence is unique to young sock-
eye and as a consequence sockeye fre'quently face problems
quite unlike those of other species of salmon. The lake
. ----··-----~--·---·
habitat, for example, makes available to sockeye a vertical
dimension in fresh water not accessible to stream-dwelling
coho ( 0. kisutch) and chinook (2.. tsha wytscha) salmon, or
to pink ( 0. gorbuscha) and chum (..Q. ~) salmon which
leave fresh water as fry. Within this vertical and sometimes
stratified habitat, sockeye are capable of occupying the sur-
face (Foerster, 1925), the epilimnion (Ricker, 1937), the
region of the thermocline (Ricker, 1937), or the hypolimnion
( Krogius and Krokhin, 1948) as food supply dictates. Living
over a wide range of depths requires concurrently living over
a range of pressures. Pressure and pressure changes accom-
@ . . panying vertical movements present sockeye with a number of
problems. These include: tolerance to positive pressure,
tolerance to decompression, initial filling of the swim bladder,
maintenance of neutral buoyancy or plane of least effort,
gain and loss of swim bladder gas, regulation of compensatory
swimming, manner of escape response and gaseous equilibration
with the environment. The purpose of this study was to
determine how these problems are met by young sockeye
salmon.
There exists now an extensive and widely scattered
literature on the perception and response of fish to pressure
and the effects of pressure on fish. This literature was
assembled and reviewed concommitant to the experimental
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study and is included here. This will be presented following
the experimental study on sockeye salmon.
The thesis is advanced that sockeye salmon meet
the problems accompanying residence and movement over a
range of pressure by adaptation, compromise and fortuity,
by means that are anatomical, physiological and ethological.
CHAPTER II
METHODS
General
The study of pressure in the early life .. history of the
sockeye salmon, Oncorhynchus nerka, was conducted in the
main at the field laboratory of the International Pacific
Salmon Fisheries Commission, at Cultus Lake, British Colum-
bia. Cultus Lake (Fig. 1.) has an endemic race of sockeye
salmon which for many years has been enumerated both during
downstream smolt and upstream adult migrations. The count-
ing weir is located on Sweitzer Creek close to the lake out-
let. Sea ward migrating smelts enter a trap in the weir,
usually within minutes after leaving the lake. Experimental
animals were obtained from this trap. The bulk of the down-
stream migration takes place during the months of April and
May but lesser numbers of smelts were trapped during March,
June and July (Fig. Z). For this reason most of the exper-
imental studies were conducted between March and July dur-
ing 1959, 1960 and 1961.
Certain aspects of the study did not require actively
migrating fish and hence a number of smelts were held beyond
the time of downstream migration, to extend the period of
investigation. Sockeye eggs were hatched in the Gultus Lake
Trout Hatchery and reared to smolt size. Studies on the
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effects of pressure from fry to smolts were conducted on
these fish. Studies involving dissolved nitrogen in fish blood
were performed on rainbow trout, Salmo gairdneri 9 from the
Cultus Lake Trout Hatchery.
Much of this study was conducted using a large pres-
sure chamber (Fig. 3), illustrated diagramatically (Fig. 4).
This consisted of a steel cylinder three feet in length and one
foot in diameter. One end was fitted with a removable
flange secured by bolts. Water of predetermined temperature
was drawn from a reservoir beside the apparatus. Pressure
was applied by means of a pump and regulated with valves
and a by-pass over the range of 0 to 300 psi (pounds per
square inch) above atmospheric pressure, the equivalent of
0 to 680 ft of hydrostatic head.
Pressures below atmospheric were investigated by
means of·a smaller cylinder, connected to the top of the
pressure chamber, in which a vacuum was produced using a
second pump. This provided negative pressures over a range
of 0 to 29.5 in Hg of vacuum, or 12 to (/160 mm Hg absolute
-~------------pressure o Positive and negative pressures were mreasured
with a Statham Pressure Transducer (range 0 to 500 psi
absolute) installed in the wall of the chamber. Magnitude
of positive and negative pressure and rate of change of
C.
Figure 1.
FIELD
LA80RATORY •
0
CULTUS LAKE
SCAL( IN MIL(S
Cul tus Lake, Brit ish Col urn bia, site of the
investigation of prPss~..:.rr-in the -life history
or the sockt:yP. /'l..fter· dcker (l'JJ'/).
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Cit ... • • •
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MARCH
Figure 2.
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MAY
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(X) •
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15 30
. JUNE JULY
Lail~; mie;ratior. of sockt:Yf' srnolts from Cultus Lake
during t v/0 years of th<:= study. !'<ate: I den tical
values in 1'-)cC; art estimatc·s hased on partial counts •
•
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Figure 3. Pr.essure cr.am l;pr loca t~~ct close to the ·,.:eir on
SviPltzer Creek.
(
VACUUM
TANK
PRESSURE CHAMBER
VACUUM _j
c:~~§§~~~====~=P;UMP
INFLOW SPOUT
IFISH+WATER)
SECTION
PRESSURE CHAMBER
BY-PASS VALVE
RESERVOIR
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pressure were recorded on a Brush Oscillograph linked through
an amplifier to the pressure sensitive transducer.
Fish were poured into the opened chamber through a
removable spout. The chamber was held half-filled with water
during this procedure by a low~ hinged baffle close to the
removable flange. Fish were kept free of inflow and outflow
vents by fine screens. Once the fish were inside the chamber
the removable flange was secured in place. Pressure within
the chamber was observed on one of three gauges: 0 to 15
psi, 0 to 50 psi or 0 to 400 psi, depending on the magnitude
of pressure under study. The apparatus permitted· conditions
.of either static pressure or water flowfug through the cham-
ber under pressure. The volume of the chamber ( 67 liters)
was sufficient to allow a small number of smelts to be held
several hours under static water conditions. Also under sta-
tic conditions the gas content of the water in the chamber
could be increased to 140 per cent of air saturation by pump-
ing air under pressure into the bottom of the chamber.
The ends of the chamber were fitted with plastic
ports 6 in in diameter, making possible observations on the
fish within the chamber. Some difficulty was experienced in
viewing fish smaller than smelts. Such fish were placed in a
2-or 4-liter glass beaker, the mouth of which was covered
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with a fine screen and the beaker inserted into the chamber g
With the base of the beaker against the viewing port it was
possible to observe small fish close at hand g Fish were re-
moved from the pressure chamber by first draining the water
to the level of the internal baffle, removing the end flange,
attaching a second spout and raising the hinged baffle. Water
plus fish pnured out into a container held at the base of the
spout.
Fish-holding facilities consisted of troughs and ponds
at the Cultus Lake Trout Hatchery, 36 holding boxes floated
in Sweitzer Creek, portable holding cages placed in nearby
Hatchery and Spring Creeks, and a number of 40-and 75-
liter plastic tubs located at the field station. The latter
were placed in a large, temperature-regulated water bath.
Pressure in Relation to Behavior
Pressure above atmospheric induced compensatory swim-
ming, that is, increased upward swimming in response to neg-
ative buoyancy. This was apparent from the marked change
-in posture of the animal (Figs. 5 & 6). The angle of inclin-
ation to the horizontal increased with increasing pressure.
Concurrently young sockeye made increased use of the pectoral
fins in maintaining position. This beating of the pectorals was,
------------"--------------------~---~--· -"-"-~
12
:;;:aractt ris7ic p· ~;t·:!'' lJ;· .sock-:·yf• salmon smc:llts at.
at mosph· ·ric pr• S~d r• 1pp•·r .1 and at a pn ssu.r•· of
5·~1 psi at.ovf· at.rnospb_ric (Jo·.:er).
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pectoral fin rate in
· beata per minute·
( appraa.) ·' ·
pre11ure
.. 3 x atmoapheric
/
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~ ; 2 x atrnoapheric
atinotpheric ': 162
-J atmoapheric
173
Figure 6. Posture and rate of pectoral fins of a smolt at
'':
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. \
pressures above and below ·atmospheric. Note: this
smol~ failed to emit gas at pressures below atmos-
pheric;: and swam downward in response to posit.ive
bouyancy.
•
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14
quantified by timing with a stop watch, to the nearest 0.1
sec, the time required for 20 strokes of the pectoral fins of
a given fish o Fish were tested in samples of 2 or 3 easily
identifiable individuals. Pectoral fin counts were made at 5
psi intervals from 0 to 50 psi, at 10 psi intervals from 50 to
'
100 psi and at 50 psi intervals from 100 to 250 psi. Counts
were made only when individual fish were actively swimming
upward. Nevertheless considerable variation was observed
among repeated counts on the same fish. In practice the
pressure was raised after pectoral counts had been made on
each fish in the group. This required 5 to 20 min at each
pressure and the total series required 2 to 3 hr. At the end
of a series the pressure was returned to atmospheric con-
ditions and the pectoral activity of the fish re-determined o
Tests were conducted on artificially incubated fry and on fry
dug from the spawning grounds before filling of the swim-
bladder, fingerlings from fry to smelt stages, on one-year-old
smelts, eighteen-month-old fingerlings and two-year-old smelts.
Tests were conducted at temperatures ranging between 4 7 to
51 o F. The tests commenced within the range of 4 7 to 49 °
F, but the temperature increased slightly at high pressures
due to pumping energy appearing as heat.
The capacity of the experimenter to count the move-
ments of the pectoral fins was established in two ways. The
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15
. ability to count a flashing light was determined using a Stro-
botac Type 1531-A stroboscope o The rate of flashing of the
instrument was selected by an assistant and the experimenter
timed 20 flashes by stop-watch. With practice 1 little dif-
ficulty was experienced counting rates up to 4 per sec ( 240
per min} o At rates above this 1 counting soon became impos-
sible. The approximate ranges of pectoral fin activity were~
fry 200 to 250 beats per min, fingerlings 150 to 220, one-
year smelts 150 to 180 and two-year smelts 100 to 140 beats
per min. Thus only sockeye fry proved difficult to count.
The accuracy of the counting methods was verified by means
of the strobe light. Due to the small size of the pectoral
fins it was not possible to use the instrument as a strobe-
scope in the dark in the usual fashion and hence have the
moving object "stand still" when the two rates were syn-
chronous. However with regular counting illumination in the
chamber it was possible to synchronize the flashing light with
the beating of the fins and hence use the stroboscope as a
device for measuring frequency. This method agreed closely
with fin rates obtained by visual counts timed by stop-watch.
Pressure in Relation to the Swimbladder
Measurements on the Fish
The measurement of pressure-induced changes in
f:l!.t.~. '<fiY/
(
16
density of sockeye was based on a knowledge of the density of
the fish and the volume of the swim bladder a The calculation
of the volume of the swimbladder required an accurate mea-
sure of the ·volume and weight of the fish o
Determination of volume. The volumes of the fish were
determined by a variation of the displacement methode An
individual smelt was allowed to drain for approximately 10 sec
with the nose on blotting paper while held by the tail a The
fish then was lowered into a glass tube, 2 o 5 em in diameter
and partly filled with water. The tube was filled until the
center of the meniscus just touched a needle-point suspended
from the top. The fish was removed and again allowed to
drain for 10 sec with the nose touching the surface of the men-
iscus. The volume of water displaced by the fish was deter-
mined by filling the tube from a micro burette o Ten deter-
minations were conducted on a single fish, the animal being
returned to experimental holding conditions between tests. For
a mean volume of 5.242 ml, 1 standard deviation was ~0.065 ml
or 1.25 per cent and for 2 standard deviations ~0.127 ml or
.:!:.2. 42 per cent.
Determination of weight. The sockeye under study
were weighed to the nearest 5 mg. Ten determinations on the
same fish employed in the measurement of volume resulted in a
mean weight of 5. 233 g with +0. 038 g or ~0. 73 per cent for 1
-)
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standard deviation and .:!:,0.07~ g or .:!:,1.41 per cent for 2 stand-
ard deviations •
Determination of density. Initially the densities of the
fish were calculated from the data on weights and volumes as
found above. Ten calculations of the density of the same fish
yielded a mean value of 0. 999 g per ml, with .:!:,0. 014 g per ml
or .:!:,1.40 per cent for 1 standard deviation and .:!:,0.027 g per ml
or .:!:,2. 70 per cent for 2 standard deviations.
In view of the relative inaccuracy and the slowness of
the weight-volume method, an alternative technique was tested.
The density of the young sockeye was determined indirectly by
establishing the point of neutral buoyancy in salt water baths
of known density. A series of solutions of salt water was
prepared by means of oceanographic hydrometers and the tables
of Zerbe and Taylor ( 1953). Salinity increments of 2. 5 parts
per thousand were used over the range of densities studied.
This corresponds to density differences of approximately 0. 002
g per ml between baths. Some further refinement was pos-
sible by observing the sinking or buoying of a fish in adjoining
baths and inte.rpolating. Occasionally fish showed densities
slightly below that of water and these were determined in 0. 5
and 1. 0 per cent solutions of ethanol.
18
In practice an electrically stunned or anesthetized fish
was transferred to the salt baths and moved up or down the
series to the nearest neutral buoyancy. In the studies of
sockeye sounding behavior it was possible to estimate quite
closely the density of the fish during the period of gas loss
and relatively few transfers from bath to bath were neces-
sary. Contamination was minimized by draining excess fluid
from the fish before transferring, by having the volumes of
the baths large ( 1 liter) in relation to the fish ( 5 g) and by
keeping the baths covered to reduce evaporation. Nevertheless
it was necessary periodically to test the specific gravity of
the solutions and replace them as change took place. The
specific gravity of salt water changes appreciably with tern-
perature and that of the baths was corrected to the nearest
5° F.
This method of density determination was more rapid
than the weight-volume procedure and did not necessitate kill-
ing the experimental fish. Ten determinations on the same
fish yielded a mean density of 1. 0003 g per ml with .:!::,0. 0004 g
per ml or .:!::,0. 04 per cent for 1 standard deviation and +0. 0008
g per ml or +0. 08 per cent for Z standard deviations. In the
range of densities close to fresh. water, solutions of inter-
mediate values were inserted between the 0. OOZ g per ml
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19
increments. This resulted in a higher degree of accuracy than
was true of the density series over the complete range. As
the fish described fell within the range of 0. 001 g per ml
increments, the accuracy expressed is approximately twofold
too great. It is probable that the method is consistent to
within +0 .1 to .::,o .z per cent, for Z standard deviations, over
the complete range of densities studied.
Measurements on the swimbladder
Volume of the bladder. A knowledge of the volume of
the swimbladder was required for the calculation of pressure
within the swimbladder and the extensibility of the bladder.
Measurement of the volume of the swimbladder in the physo-
stomous sockeye was complicated by the tendency of these fish
to lose a portion of the gas from the swimbladder when dis-
turbed. This property of the fish required swim bladder volume
to be calculated in two ways, -one, where bladder volume was
employed in the calculation of pressure within the swim bladder,
and another in the calculation of distensibility of the bladder.
In the former the statistic required was the actual volume of
gas in the bladder, regardless of the degree of inflation this
represented. In the latter method it was necessary to cal-
culate extensibility of the bladder from the volume the swim-
bladder would have been, had the fish been at neutral buoyancy.
20
Both methods of calculation of volume of the bladder are based
on the definition of density g
density = weight
volume
As the weight of the fish is constant, for all practical pur-
poses~ with the swim bladder empty or inflated with gas, den-
sity may be related directly to volume~
where Dr is the density of the fish, swimbladder par-
tially inflated e
DD is the density of the fish, swimbladder
deflatede
VFr is the volume of the fish, swim bladder par-
tially inflated
is the volume of the fish, swim bladder
deflated
where VB is the volume of the swimbladder at the mea-
sured density and volume.
Substituting~ Do x (VFr -Va) = Dr x VFr
DD x VFr -DD x VB = Dr x Vpr
-DD x VB Dr x Vpr -DD x Vpr
VB=
DD x Vpr -Dr x Vpr
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21
The value "deflated density" ( Dn) was determined on 60 smelts.
The procedure was to remove the gas from the swimbladder of
the intact fish by means of a fine hypodermic needle and small
syringe o The volume and density of the fish was determined
and the fish then was dissected open mid-ventrally under water.
If any gas remained in the swimbladder it was removed and the
density re-determined o The mean gas-free density .;,as 1. 0634
g per ml with .:!:.0. 0015 g per ml for one standard deviation o In
view of the consistency of the method this mean density was
subsequently used throughout for the calculation of volumes of
swim bladder. Thus initial density and initial volume of the fish
were all that remained to be measured before the volume of
the swim bladder could be calculated. For example, where the
initial density of the fish was 1o 0177 g per ml and the initial
volume of the fish was 6 o 812 ml, the volume of the swim-
bladder was:
6.812 X (1.0634 -1.0177)
1. 0634
V 8 = 0.293 ml
The above value represents the volume of gas in the
swim bladder at the described conditions of volume and density,
ignoring pressure for the moment. Thus this is the volume
(1~:. . .
'· ·: ...
22
most appropriate in any comparison of experimental and thee-
retical (Boyle's Law) expansion of gas in the swimbladder.
However, because of the tendency of the sockeye to
lose some of the gas from the swim bladder, volumes as de-
rived above are not applicable i~ ·the determination of extensi-
bility of the swim bladder. That is, if a smelt lost one-half
of the gas from -its swimbladder~ a subsequent reduction in
pressure to one-half the former level would merely 'take up
the slack' and restore the bladder to its original size. Thus
it was necessary to calculate also the volume the swimbladder
would have been were the fish at neutral buoyancy. This is
based on the formula as derived above:
( 1)
where VBN is the volume of the swimbladder at density
1.0000 g per ml (neutral buoyancy)
V FN is the volume of the fish at density 1. 000
g per ml
Dn is the density of the fish, swimbladder
deflated to density 1. 0634 g per ml
DN is the density of the fish, swimbladder
inflated to density 1. 0000 g per ml
(2)
where VB is the volume of the partially-inflated swim-
bladder as determined above.
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or
Substituting
VFN = VBN -VB + VFI (3)
VFN of equation (3) to ( 1) we obtain the
formula~
= (VBN-VB +VFI) x (DD-DN)
DD
23
from which may be calculated the volume the swimbladder would
have occupied had it been inflated to provide the fish with neu-
tral buoyancy o Employing the values of volume and density as
used in the example above:
(VBN -Oo293 + 6.812) X (1o0634-1oOOQ)
1. 0634
Ambient pressure o Alexander ( 1959) described a method
for determining the ambient pressure within the swimbladder of
live, anesthetized physostomes o In principle the technique per-
mits a comparison of gas compressed within the swimbladder
with the same gas compressed outside the bladder and hence
free of any confining influence due to the swimbladder itself.
In the present study the apparatus (Fig. 7) was patterned
closely after that of Alexander o Individual sockeye were per-
mitted to fill their swimbladders to neutral buoyancy in shallow
water, then were exposed gradually to an anesthetizing dose of
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----------------.. ---: ------' -. --:: ----r ---' -
mercury
manometer
in Millimeter•
H~torotorJ , .....
vacuum or
pre11ure
r;=.::::::= pump
pretture
equalizlno
flaek
menitcut
calibrated
tube
flotk filled
with onattthttic
tol"tion
Figure 7. Apparatus for the measurement of ambient
pressure within the swim bladder. (After .
PJexander (1959).
•
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25
tricaine methane-sulfonate (Sandoz MS -222). This pro-
cedure was essential to avoid fright-i.nduced loss of gas from
the swimbladdero The density of the anesthetized fish was
determined prior to placing it in the apparatus and fish which
had lost gas were not tested o With the fish inside, the
apparatus was sealed and the volume of water adjusted until
the meniscus was located satisfactorily in the calibrated tube o
Pressure in the flask and hence on the fish was increased in
increments of 30 mm Hg above atmospheric pressure and the
displacement of the meniscus recorded o On reaching 360 mm
Hg, the pressure was lowered to atmospheric and thence in
similar increments to 360 mm Hg below atmospheric or until
one-third to one-half of the gas had escaped from the swim-
bladder o This gas was trapped in the top of the flask. The
pressure was returned to atmospheric and the increments of
positive and negative pressure wer:e repeated o
The apparatus was standardized after each determin-
ation for both the positive and negative range and the exper-
imental values were corrected for this distortion of the
apparatus o The gas content of the water used in the appar-
atus was reduced artificially by prolonged exposure to a par-
tial vacuum to minimize the tendency of the gas to leave
solution when the pressure was reduced below one atmosphere o
26
There was little evidence of gas leaving solution under the test
conditions nor was there any evidence of gas in the top of the
chamber entering solution at pressures above atmospheric.
Blank-corrected values of compression and expansion of
the swim bladder were plotted against pressure (Fig. 8).
Excess pressure within the swimbladder at atmospheric pres-
sure was represented by the horizontal difference between the
two curves.
Extensibility of the bladder. Extensibility was measured
in an apparatus (Fig. 9) based on that which Jones (1951) em-
ployed on physoclistous perch. The tendency of physostomous
sockeye to lose gas from the swimbladder through fright neces-
sitated use of fish just killed either by anesthetic or electric
shock. Another problem was upward escape of gas through the
apparatus • This required the calibrated tube to be of suffic-
ient diameter such that bubbles of gas could pass up the tube
without forcing liquid out through the top. This requirement
limited the minimum diameter of the tube and as a consequence
calibration could not be read more closely than 0. OZ ml.
In practice an individual fish was killed and its density,
volume and weight determined. The fish was placed in the
apparatus and exposed to a gradual reduction in pressure.
Volume of the fish was recorded for increments of pressure
reduction of 2. 5 in Hg ( 63.5 mm Hg) from atmospheric
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. 27
lwimbladder pre11ure
20 nun H9
(A a 8) o 9a1 in swimbladdtr
(C a 0) • 9a1 partly in IWimbladdtr
and partly in tla1k
-240 -120 0 120 240
PRESSURE IN MILLIMETERS OF MERCURY
360
Figure 8. Calculation of excess. pressure within the. swim bladder.
•
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r--------~r----6=-vacuum pump
vacuum gauge
inches Hg
sockeye smalt
Figure 9. Apparatus for th'~ mE-asurement of the pressurP
required to force gas out through the pneumatic
duct. After .__Jones ( 19')1).
•
26
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29
pressure to a vacuum of 27 o 5 in Hg ( 698 o 5 mm Hg) o Obser-
vations on first evidence of gas loss, size and frequency of
bubbles and rising and sinking of the fish were recorded o The
apparatus was calibrated regularly over the range of vacuum
studied and individual values for a fish were corrected for
vacuum expansion by the apparatus o
Volume of the swimbladder was derived as explained
previously and theetheoretical expansion of the gas was calcu-
lated using Boyle's Law o
is atmospheric pressure or 29 o 92 in Hg
is the volume of the swimbladder at atmos-
pheric pressure
is the pressure in in Hg at any given reading
is the calculated, theoretical volume of the
swimbladder gas would occupy at the new
pressure, P 2
Thus for example, if the initial volume of the swim-
bladder was Oo412 ml, then at a vacuum of 2.5 in Hg (693 mm
Hg absolute pressure) the theoretical volume of the swim bladder
would be:
29o92 0.412 0.449 ml = 29o92-2o5
30
The theoretical volumes were calculated for each of the 12
increments of pressure reduction and together with the obser-
ved values were plotted as in Fig. 14.
Extensibility of the swimbladder was calculated as a
per cent of the volume the swimbladder would occupy at
atmospheric pressure and for a density of 1. 0000 g per ml.
This was calculated for individual fish up to the point of re-
lease of gas from the pneumatic duct or rupturing of the
swim bladder. Thus the fish described in previous examples
with swimbladder volume of 0.412 ml (at density 1.00003 g
per ml and atmospheric pressure) lost gas from the swim-
bladder at an expanded volume of 0.473 ml or at 115 per cent
of neutral-buoyancy volume.
The technique described above was employed on three
series of fish under control conditions comprising 10 individual
smolts in each series. The influence of the body wall was
explored in a series of 10 fish in which a mid-ventral incision
permitted unrestricted expansion of the swim bladder.
Contractibility of the bladder. Loss of an appreci-
able quantity of gas from the bladder by sockeye smolts when
frightened suggested two possibilities. Firstly, t:;hat gas loss
may be through active expulsion by contraction of the bladder.
Secondly, being a fright· response loss of gas may be under
autonomic control. These two possibilities were examined
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31
concurrently through the use of pharmacological agents on
isolated strips and intact swim bladders.
Autonomic drugs do not act on autonomic nerves, as
the name suggests, but rather on effector cells such as mus-
cle or gland cells (Goodman & Gilman, 1955). Thus the nerves
to the duct or bladder need not be intact for study with auto-
nomic agents. Four types of autonomic drugs were utilized:
sympathomimetics, drugs such as adrenaline and ephedrine which
stimulate structures innervated by adrenergic nerves; adrener-
gic blocking agents such as 11 dibenzyline"; parasympathomimetics,
drugs such as acetylcholine and pilocarpine stimulating structures
with cholinergic innervation; and cholinergic blocking agents such
as atropine. In general these agents were tested at concen-
trations of 10 mg per ml, abbreviated to 10-5 or 1 in 105.
This is the standard method of expressing the concentration of
drugs in baths (Lewis, 1960).
Isolated swimbladders initially were suspended longitud-
inally within aerated frog Ringer's solution in a muscle-:Prepar-
ation apparatus. Subsequently cross-sectional loops were cut
out from the swimbladder and suspended within the muscle-bath
such that a reduction in cross-sectional area would openate .,
the writing lever. These tissues were tested with adrenaline
(10-5) and ephedrine (1o-5) before and after adrenergic
blockade was attempted with 11 dibenzyline" ( 10-5). By-passing
32
of "dibenzyline" blockade was attempted with monoacetin at
concentrations of 1o-5, 10-4 and 10-3 » followed by adrenaline
( 10-5) o Pilocarpine and atropine were tested on fresh tissues
at doses of 10-5 o All tests were conducted on the swim-
bladders of 18-month-old sockeye fingerlings o Bath temper-
atures were maintained between 45 and 50°F 0
The response of the intact swimbladder was investi-
gated using the same pharmacological agents as above o Individ-
ual sockeye fingerlings were stunned electrically and then killed
in a strong dose of anesthetic o The fish were opened mid-
ventrally under physiological saline, exposing the swim bladder o
With the abdominal walls held apart, a small amount of drug
such as adrenaline was added to the saline in the region of the
swimbladder o The response of the swim bladder was noted plus
any movement of gas through the pneumatic duct and out the
mouth o The adrenaline was washed a way and the tissues
exposed to 11 dibenzyline 11 , re-washed and re-treated with
adrenaline. Additional fish were tested with the drugs pilo-
carpine and atropine o In these intact swim bladder studies it
was essential that the fish be kept under water (physiological
saline) to detect the movement of gas out of the swim bladder.
This made impossible close definition of the concentration of
drug in contact with the· swim bladder.
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33
Gas secretaion. Fish in general respond to increased
pressure and hence increased density by secretion of gas into
the swimbladder whereas decompression and positive buoyancy
are followed by resorption of gas. The extent of these pro-
cesses in young sockeye was investigated at atmospheric pres-
sure and pressures above atmospheric,. In such studies on
sockeye salmon it was essential to preclude access to atmos-
pheric air to be certain air had not entered the swimbladder
via the pneumatic duct. That is, there fish utilize atmos-
pheric air for swim bladder inflation where possible. It was
possible to deny atmospheric air to experimental fish and hence
one could infer that any gain in volume of gas would be due to
the activity of the swim bladder. The converse, of course,
was not readily possible in physostomous sockeye. Gas lost
from the swimbladder by way of the pneumatic duct would tend
to mask gas resorption through the swimbladder.
A group of 10 smolts was placed in a 7 5 liter container
and induced to sound to the bottom through a disturbance on
the surface. This fright-induced sounding response was accom-
panied by loss of gas from the swim bladder. The density of
the fish increased accordingly. A screen was placed over the
fish, halfway down the container, thus preventing the smolts
from utilizing atmospheric air (Fig. 10). A second group of
fish was treated similarly but these fish were stunned
CONTROL
GAS
RECOVERY
TEST
GAS
RECOVERY
i in m .. h tcrttn
CONTROL
GAS
LOSS
--------
J4
Figure 10. Investigation of inflation of the swim bladder with
and without access to atmospheric air.
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electrically after covering with a screen o In this case the
density of the sockeye was determined immediately and these
fish served as a check or control on the gas lost by the
group held below the screen. A third group of 10 sockeye
was placed above the screen, similarly induced to sound and
then allowed free access to atmospheric air during the period
of holding o Groups of sockeye were held in this way for per-
iods of 0, Z, 4 and 8 days. At the end of these periods
the fish were stunned electrically and the density determined o
After studying effects of atmospheric pressure as
described above, the possibility remained that higher pressures
may induce secretion of gas by the swim bladder o Holding fish
under pressure in the apparatus, as described under general
methods, presented no difficulty. There was however the
serious problem of determining the density of the fish before
and after prolonged holding under pressure 0 For this purpose
the Cartesian Diver principle was employed, patterned after
the method of Tait ( 1959). Initially it was necessary to
relate smolt density to vacuum. This was done by determin-
ing the density of an individual, freshly killed smolt o The fish
was placed in the chamber and the pressure reduced until the
fish was suspended in mid-water o The vacuum necessary to
bring the fish to neutral buoyancy was recorded o This pro-
cedure was repeated for a range of fish densities and plotted
36
as in Fig. 11. The curve is considered reliable to a vacuum of
approximately 20 in Hg P beyond which gas leaving solution tends
to form bubbles on the surface of the fish. Thus the density
of a fish could be determined by applying a vacuum of suffic-
ient magnitude to expand the gas within the swimbladder and
suspend the fish in the chamber. This was most readily done
with the fish immobilized. The steel chamber conducted away
any electric current applied within it and thus made impossible
electrical stunning of the fish. The use of anesthetics was
tested but proved costly and difficult to apply because of the
flow pattern within the pressure chamber.
It was decided finally to apply the Cartesian Diver
technique to conscious fish when they were resting quietly.
Thus an individual sockeye was placed in the apparatus, the
chamber was filled with water and the fish was allowed time
to become quiet in familiar surroundings. Because swim bladder
gas was lost with excitement on entering the chamber, the
fish were slightly denser than water and the fish were not
permitted atmospheric air for re-inflation of the swim bladder.
The initial density of the fish was determined by a reduction
in pressure and subsequent buoying. The fish was then put
under a pressure of 1 or 3 atmos above atmospheric and held
24 hr o At the end of this time the pressure was reduced to
atmospheric and then gradually below that o The point of
1.07 I I I I '/o
•.. 06 -/00 -
0:
"" t-1.05 -0 -
"" / 2
t-/0 z
"" 0
1.04 -..,.
0 /0 -CD
::>
0 fO
ffi 1.03 -;/ -
0..
(/)
2 c:r /0 0: -C) 1.02 ~
z
>-t-0
~ 1.01 ~ y -
"" 0 /0
1.00 r'o -
Q99~---------._·-------~·~--------~·--------L'---------1~---------
o 5 10 15 20 25 299
VACWM IN fNCHES OF MERCURY
Ftgurc-1 1 !. !. • 3molt d•.·nsity a:td magnit udoc-of vacuum nr>cessary
•
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.\
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38
neutral buoyancy of the fish was recorded and gain or loss of
gas was interpreted from any change in density o
Measurements on the paeumatic duct
Gain and loss of swimbladder gas through the pneumatic
duct could be expected to have important consequences for the
fish. There is firstly the value of the sounding response as
a mechanism of escape. Secondly 7 mortality of fish on decom-
pression may be due to the entry of gas of swimbladder origin
into the blood stream (Jones and Marshall, 1953) o Thus the
effects of decompression may be dependent on the degree of
inflation of the bladder. Thirdly, the compensatory swimming
of young sockeye would be expected to relate to the density
of the fish, which is a function of degree of inflation of the
bladder and pressure o For these reasons an attempt was
made to quantify loss of gas on sounding and to establish the
nature of the regulation of entry and loss of gas through the
pneuma tic duct o
Loss of. gas on sounding. The ·sounding response of
sockeye salmon smelts was readily apparent o When startled
the fish dived immediately leaving an obvious trail of gas bub-
bles. This loss of gas from the swim bladder resulted in a.::
:corresponding increase in density o The sounding response was
quantified by measuring the density of the fish at the end of
. gas emission o
l
1
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39
The ·stimulus to sounding was standardized by having
the fish sound in a 4-liter-cylindrical-glass jar (Fig o 12). A
smolt so tested always sounds to the bottom 1 all the while
releasing small bubbles of gas. Loss of gas is completed
·usually within 30 sec o In the exploratory tests fish were
stunned electrically after 2 min and then removed for density
determination o Subsequently it was found simpler to use an
anesthetic solution of MS-222 in the jar 1 the strength being
adjusted to produce anesthesia in about 2 min. Fish densities
were measured in the series of salt baths described previous-
ly.
Once the sounding response had been quantified, it was
possible to explore the mechanism of loss of gas from the
swim bladder. Several pharmacological agents, with known auto-
nomic effects in the higher vertebrates, were tested on sock-
eye smelts in an attempt to establish the nature of the con-
trol of the swim bladder and pneumatic duct o Sympathomimetic
and parasympathomimetic agents plus sympatholytic and para-
sympatholytic drugs were tested. Relatively stable agents
such as ephedrine and pilocarpine were used in preference to
epinephrine and acetylcholine respectively. In practice, the
agents were tested in simple solution, over a range of concen-
trations up to the level of initial mortality. Following this
preliminary screening, drug doses well below the lethal level
c
(.
LIGHT SOURCE
r
DARK BACKGROUND
•
SOLUTION OF
ANESTHETIC
Figur~ 12. Apparatus uSt.'d to inducf~ the soundiug response
in soc kt•yf-=--smol t s.
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41
were explored. Where an effective dose was found 1 a time-
response curve was established for the period of 1 to 12 hr.
Fish were tested in groups of 10 after periods of 1 » Z, 3,
4, 8, and 12 hr of exposure to a drug in solution. Control
fish were held in similar containers of water and were tested
concurrently for sounding response. In so far as was pos;..
sible 1 the 60 test and 60 control fish were drawn from the
migration as one large sample and treated identically but for
the addition of the drug to the holding water of the test
group.
The drug ephedrine, an effective sympathomimetic
agent, was tested and the response determined at concentrat-
ionsoof 100 and ZOO mg per liter. "Dibenzyline" 1 a potent
adrenergic blocking agent (Nickerson and Goodman, 194 7) , is
accredited with a solubility in water of approximately 0. 1 mg
per liter. This concentration showed no effect on sockeye
smelts and the dose was raised tenfold to 1. 0 mg per liter.
Some change in gas loss was evident at this concentration.
The drug was re-tested at 5o 0 mg per liter with the effects
described under results. No explanation is offered for the
effectiveness of this drug at a concentration of almost 50
times its supposed solubility o A second, otherwise unrelated
adrenergic blocking agent 11 hydergine 11 (a mixture of three
ergot alkaloids, Goodman and Gilman, 1955) was tested at
42
concentrations up to 10 mg per liter.
The effect of cholinergic stimulation on the sounding
response was investigated using the parasympathomimetic drug
pilocarpine. The cholinergic blocking agents 11 darbid" ( iso-
propamide iodide) and atropine were tested at concentrations
of 100 and 200 mg per liter respectively. A discussion of the
pharmacology of "darbid" may be found in Proddsdiji-Hartzema,
Janssen and Jongh (1955).
f?ulping atmospheric air. The filling of the swim bladder
by gulping of air at the surface, the "Luftschluchen" reflex,
was examined first in relation to pressure changes and::·aub-
sequently in regard to nervous control. The methods employed
in the study of the nervous control of emptying of the swim-
bladder were . not applicable readily to the study of inflation of
the swimbladder due to the complication of fright-induced loss
of gas. Two alternative methods of study were devised.
In the first approach, groups of 10 smelts each were
placed in 70 liter containers, induced to sound by means of a
disturbance on the water surface, then denied access to the
surface by means of a screen, as described previously. A
drug could now be put in solution in the water containing the
test fish and the fish exposed to it for some period of time.
At the end of this time . the control group was stunned elec-
trically, still under the screen and their individual densities
J
I __ ,,~ ···~_-·;~;
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J
43
determined. This established the extent of loss of gas from
the swim bladder which had occurred on sounding. The screens
were then removed from the remaining containers, permitting
the test and second control groups access to the water sur~
face. After 5 to 10 min these fish were stunned electrically
and their densities determined. The second control group,
the individuals of which almost invariably returned to neutral
buoyancy in the few minutes air was available, provided the
basis of comparison for the drug-exposed fish. The periods of
holding under the screens ranged from 1/2 to 4 hr. Holding .
such fish for one or more days resulted in a much slower
return to the use of atmospheric air when the screens were
withdrawn. The drugs tested in this study were the same
doses of adrenergic and cholinergic stimulants and blocking
agents used in\the examination of loss of gass on sounding.
A second method of investigating the gulping of atmos-
pheric air and inflating of the swimbladder was devised to
verify the results of the under-the-screens studies. In
principle the swimbladder was provided with an accessory open-
ing to the exterior of the fish, such that air which entered
the swim bladder escaped via the auxiliary duct. Individual
smolts were anesthetized with MS-222, then the anterior half
of the fish was isolated from the posterior half by means of
a rubber diaphragm. The anterior end of the fish was
44
maintained in a narcotizing solution of anesthetic, leaving the
posterior half of the fish available for surgery. A short length
of fine polyethylene tubing was inserted in the swimbladder
through the left side of the fish slightly anterior to the vent
and below the lateral line. The catheter was secured in place
by a small stitch through the adjacent musculature and term-
ina ted in a tie around the circumfe;eence of the fish. Whether
or not the catheter ended within the lumen of the swim-
bladder was apparent by the response of the fish on recovery
from the anesthetic.
Properly catheterized fish rose to the surface of the
water, mouthed a bubble of air and angled downward toward
the bottom of the aquarium. Concurrent to the change in
position from head up to one of head down, a series of bubbles,
about six in number, issued from the external end of the cath-
eter. This procedure of swimming up to the surface, mouthing
a bubble of air, swimming downward and passing the gas into
the swim bladder (only to lose it to the outside) was repeated
every few minutes for two to three days. At the end of this
time the fish took to residing on the bottom of the tank and
ceased making excursions to the surface. This behavior is
illustrated in Fig. 13.
During the post-operative period when the fish were
actively surfacing, gulping air and losing it through the catheter,
l
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D
Fish at tempt to inflate bladdPrs
for initial t v-.ro to thre-e days (A, 3 and C),
thereafter rf_'Sidinf~ on tank bottom (D) • •
45
46
some aspects of the fishes' air-introducing mechanism were
amenable to study. In particular the nervous control of the
pneumatic duct was explored by means of pharmacological
agents in solution, especially the cholinergic and anticholinergic
drugs pilocarpine and atropine. The fish were observed most
readily while held in replicas of the salinity-preference cham-
bers of Baggerman { 1957).
Duct-release pressure. The excess pressure within
the swimbladder necessary to force gas out through the pneu-
matic duct, hereafter termed the 'duct-release pressure' was
calculated from the data on extensibility of the swim bladder o
In this case the volume of the swimbladder was obtained using
the formula:
VFI x (DD -Dr)
VB = -----------DD
as described previously. The observed expansion of the gas
in the swim bladder was plotted, as in Fig o 14, at each incre-
ment of reduction in pressure of 2. 5 in Hg { 63.5 mm Hg).
Theoretical volume of the swimbladder was calculated for each
pressure. reduction. For example, at a vacuum of 2. 5 in Hg
the volume of gas, obeying Boyle's Law, becomes
29.92 x 0.293 = 0.320 ml
29.92 -2. 5
1
1
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-]
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j
·~-----
1.1
en 1.0 e ...
2 i= 0.9
z ...
0
~ 0.8
CD :::»
0
z
......
2
:;:)""
..J
0 >
a: ....
0
0.7
0.6
0 c 0.5
..J
CD
2 -• en
·-
~ ~' gas roloaud through pnoumatlc _,
// o---o /
1
v2 ---o,,
~~ .... ~
0~ . ',
experimental '
VACUUM IN INCHES OF MERCURY
' o---o
Figure 14. Calculation of pneumatic duct-release pressure from
theoretical and observo:""'d expansion of gas in the
swfmbladder up to time of gas escape.
•
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48
Pressure within the swimbladder similarly was calcu-
lated from Boyle's Law:
where P 1 is absolute pressure in mm Hg at the point of
observation.
V 1 is calculated theoretical volume of the swim-
bladder.
P2 is pressure within the swim bladder.
v 2 is observed volume of the swimbladder.
For example, in the fish referred to above, gas escaped from
the swim bladder under conditions of:
p1 = 442 mm Hg
v1 = 0.503 ml
v2 = 0.473 ml
442 X 0.503 = P2 X 0.473
P 2 = 470 mm Hg
Having derived P 2 , the excess pressure within the swim bladder
or the net pressure exerted against the duct is simply:
Thus the duct-release pressure is approximately:
470 -442 = 28 mm Hg
The method described above was originally intended as
a means of measuring the extensibility of the sockeye swim-
bladder and was subsequently adapted to the study of the
J
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. ~
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49
pressure required for the release of gas through the pneumatic
duct. One difficulty with the method was that the pressure
with~ the swimbladder cannot be calculated for the precise
moment of escape of gas from the duct. This necessitated
the use of the observed and calculated values immediately prior
to release of gas.
The technique outlined was used in the investigation of
the nature of the pneumatic duct. Evidence was sought for
the presence of a sphinpter or some form of constriction
along the duct. Based on the known tendency of sphincters
to relax following the death of an animal, fish were killed and
the duct-release pressure was determined at various times
after the death of the fish. Drug treatments which had been
tested for their effects on the sounding· response were fur-
ther tested for their action on the pneumatic duct. Three
series of control fish, comprising 10 sockeye smelts each, were
tested during the course of the study. These groups showed
average duct-release pressures of 28.9, 28.6 and 26.9 mm Hg.
In all of these studies on the release of gas through
the duct it was not possible to use live fish, for when exposed
to a gradual reduction in pressure, conscious sockeye simply
released gas and returned to neutral buoyancy. For this
reason it was necessary ·to use as experimental animals fish
just killed by anesthetic.
50
Hi~rtological examination. The swim bladders and pneu-
matic ducts of experimental and control fish were examined
histologically. The condition of the pneumatic ducts in par-
ticular was investigated in fish treated with sympathomimetic
and parasympathomimetic agents plus adrenergic and choliner-
gic blocking agents • In addition to the examination of fish
held in drug solutions, yearling sockeye of 10 g were injected
with 0 .1 mg of these agents. These fish were anesthetized
and the tissues fixed for histological examination 1 hr after
injection.
In all fish care was given to the fixation of the tis-
sues of the duct and bladder. Fish were opened mid-ventrally
and the gastro-intestinal tract turned out through the slit,
permitting the fixative Bouins picro-formol, rapid access· to
the region of the pneumatic duct. Bladder and duct material
was routinely embedded in paraffin, sectioned and stained with
eosin and hematoxylin.
Pressure in Relation to Gases
As outlined in the introduction, upward movements in a
stratified lake present fish with the problem of an increase in
nitrogen saturation internally as a result of reduced gas-content
of the water, increased temperature, reduced pressure and
hence increased absolute saturation of the water. The
' 1
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51
investigation of this problem required methods of gas analysis
a study of the limnology of the lake environment and a mea-
sure of the tolerance of fish to decompression. Ultimately
the study came to include a measure of the rate at which fish
equilibrate with the dissolved nitrogen of their environment.
The theoretical considerations relevant to the study of
dissolved gases are summarized in Appendix A. Included in
Appendix A are the tables of oxygen and nitrogen solubilities
used in the calculation of per cent of air saturationo
The methods of analysis of dissolved oxygen and nitro-
gen in fish blood appear in Appendix B.
Limnological investigations
Site of study. Limnological investigations in relation to
the smolt migration were begun in 1960 at three stations along
the length of the lake. Because results were similar these
were reduced to a single station in the north-central part of
Cultus Lake (Fig. 1). A second was established on Sweitzer
Creek, ZOO yd downstream from the lake outlet. In 1960,
temperature and dissolved oxygen were determined vertically at
irregular intervals during the spring smo!t migration. In 1961
these measurements were made every two weeks during the
downstream migration and at three-to four-week intervals
beyond this time. Dissolved nitrogen was measured vertically
every two weeks during the smolt migration and irregularly
52
after that.
Measurement of temperature. The vertical temper-
ature structure of the lake was measured to within a few feet
of the bottom by means of an oceanographic bathythermograph.
The bathythermograph was placed in operation at a depth of
one foot below the surface and a research thermometer read
concurrently at that depth. The smoked slide from the bathy-
thermograph was located in the reading grid on the basis of the
thermometer temperature. The instrument was calibrated by
the Pacific Oceanographic Group, Nanaimo, B.C. prior to
commencement of the study.
Measurement of dissolved gases. Water samples were
collected at depths of 0, 5, 10, 15, 20, 25, 30, 40, 50 and
130 ft in one-liter limnological water bottles. The samples
were transferred to 300 ml BOD bottles. Dissolved oxygen
was fixed on station and the titration performed in the labor-
atory. Water samples were taken separately for nitrogen
analyses, transferred to previously cooled BOD bottles and
during transport held at temperatures below that of the cold-
est water sampled. In this way the possibility of gas leaving
solution as a result of warming was avoided. Nitrogen anal-
ysis was conducted in the laboratory employing the modification
of the Scholander method described in Appendix B. The
c··. amount of water required for nitrogen analysis was very small
I
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53
and oxygen determinations were repeated once on the sample
remaining.
Calculations. Oxygen and nitrogen were expressed as
mg per liter (Tables III and VI, Figs. 25 and 28). Using
the theoretical solubilities as prepared from the absorption
coefficients, Tables IX and XI, the per cent saturation was
calculated f~t'OJihconditio.ns of atmospheric or surface pressure
(Tables IV and VI, Figs. 26 and 29) for oxygen and nitrogen
respectively.
If the fish however were to migrate vertically from
temperatures at depth to surface, conditions at a rate faster
than gaseous equilibration was taking place, then: saturation of
the fish would be expressed more correctly as perc.cent of
saturation at surface temperature and pressure. For this
reason oxygen and nitrogen saturations have been expressed as
such (Tables V and VI, Figs 27 and 30). Finally, no attempt
has been made to calculate hypolimnion saturations to the cor-
responding periods of air-water equilibrium. As Hutchinson
( 1957) pointed out, few workers have regarded this refinement
as worthwhile.
Measurement of tolerance to pressure
During the downstream migrations of 1959 and 1960,
groups of sockeye smelts, numbering 200 or 300 per sample,
were tested in the pressure apparatus as described under
54
general methods o The tolerance of these fish to pressure was
explored with respect to degree, duration and rates of change o
Following testing.:; the groups of fish were held in one of the
36 cages situated in Sweitzer Creek. The fish were kept under
post-test observation for two weeks during which time any
injuries were noted and mortalities recorded. Control tests
of a similar number of smolts were conducted after every
fourth or fifth test. These fish were handled in an identical
manner, being placed in the apparatus for the appropriate time
and temperature, but maintained at atmospheric pressure. These
control groups similarly were held for two weeks for observa-
~-tion.
In the study of tolerance to pressure and the succeed-
ing study of factors influencing pressure· tolerance, a total of
143 tests involving 19,849 smolts were conducted in 1959 and
in 1960 an additional 117 tests on 13,002 smolts were carried
out.
Magnitude of positive and negative pressure. Groups
of 100 ~m 200 smolts were exposed to conditions of positive
pressure ranging from atmospheric to 400 psi ( 27 atmos) above
atmospheric o Routinely, pressures of 15, 20, 50, 100, 200
and 300 psi were tested. The pumping equipment was designed
to operate at pressures of up to approximately 300 psi and
only on a single occasion was the pressure raised to 400 psi.
~ 1
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55
The pressure range of 0 to 300 psi had been explored prev-
iously in the studies of sockeye behavior. However in the
tolerance tests the larger samples of 200 fish were held in
cages for two weeks of post-test observation as described
above. Pressure was raised at the rate of 1 psi per sec,
thus pressures of 300 psi were reached in 5 min.
Groups of smelts were exposed also to a range of
pressures below atmospheric. An attempt was made to test
these fish at vacuums of 0, 5, 10, 15, 2Q, 25 and 29o5 in Hg.
Due to the nature of the apparatus, in particular the small
water column between the vacuum and pressure chambers, it
was not possible to achieve precisely the desired vacuum o
However, the exact vacuum attained was recorded via the
transducer mounted in the wall of the pressure chamber o
Duration of positive and negative pressure. The effect
of prolonged exposure to pressure was tested only at relatively
low pressures. Samples of smelts were subjected to a pres-
sure of 15 or 20 psi above atmospheric for periods of 1, 3,
6, 12, 24 and 48 hr. At 50 psi groups were tested for short
durations, such as 5, 30 and 60 min and for longer periods of
24 and 48 hr. The pressure pump was not well suited to pro-
longed operation at high pressures and smelts were not exposed
to 300 psi for more than one hour.
56
The effect of exposure to prolonged negative pres-
sures was tested at vacuums of 10 and 15 in Hg o Periods
of exposure to vacuum were 0 .1, 1. 0, 10 and 100 sec. In
various experiments dealing with the swim bladder, smelts were
exposed to vacuums of 5, 10, J.5, 20 and 25 in Hg for periods
of 2 to 5 min. In these latter experiments however, the
fish were not subjected to post-test holding and observation.
Rate of increase and decrease in pressure. A limited
number of studies were conducted on rates of pressure in-
crease. Pressure was developed by a motor-driven roller-
pump, as described previously and this equipment was not suited
to very quick application of pressure o The most rapid rate of
increase possible was approximately 300 psi in 30 sec o:-10
psi per sec.
Groups of 200 smelts were exposed to a range of rates
of reduction in pressure from 50 and 300 psi to atmospheric
conditions o In one series, for example, pressure was reduced
from 300 psi to atmospheric pressure at intervals of 0 o 02,
0 .~, 2. 0, 20 and 200 sec, yielding rates of change of 15,000,
1,500, 150, 15 and 1o5 psi per sec.
Conditions altering resistance to decompression
Seasonal effect o Tests were conducted routinely dur-
ing the downstream migration of 1959. A sudden change in
tolerance of sockeye smelts appeared late in the migration.
1,~
1
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57
This change focussed attention on the possibility that seasonal
factors were involved in the tolerance of these fish to
changes in pressure. This was explored in the succeeding years,
1960 and 1961. Samples of smelts drawn from the migration
at one-to twe-week intervals from March to June were sub-
jected to the standardized decompression test and observed,
post-test, as described.
This standard test consisted of placing a sample of
sockeye smelts, trapped at the outlet of the lake during their
downstream migration, into the pressure chamber and raising
the pressure to 50 psi from atmospheric in 50 sec and holding
the fish under this pressure foiV 5 min. This 5 min holding per-
iod merely provided time for adjustjng valves and operating the
recorder. Thereupon the pressure was released in 0. 02 sec
to a negative pressure consisting of a vacuum of 29 in Hg and
the vacuum was maintained for 1. 0 sec. Previous studies had
shown that the brief exposure to positive pressure did not
influence the resulting injury or mortality. This phase of the
test was retained in order to make the results comparable
with earlier applied studies. and to provide a more uniform rate
of change of pressure. The magnitude of vacuum was set at
a high level to maximize mortality and hence better separate
experimental groups. The mechanism of action of this change
was explored as outlined in the succeeding sections.
------···-··---·---
58
Holding smolts at lake surface and depth. The seasonal
change in pressure tolerance of migrating sockeye was observed
in 1959 to be influenced also by the time elapsed between tak-
ing the smolts from the migration and subsequently subjecting
these fish to the standard decompression test. In 1960 and
1961 the effect of this delay before testing was explored.
Samples of smolts migrating out of the lake late in the sea-
son (June) were held in the pens located in Sweitzer Creek,
essentially in temperatures equal to the surface water of the
lake. Samples of smolts were tested after 0, 3, 6, 18, 48
and 72 hr of holding •
In 1960, a sample of 100 late-migrating smolts was
tested and the resulting mortality recorded. A second sample
of 200 smolts was held for 24 hr in Sweitzer Creek, then
100 of these were subjected to the standard test; the remain-
ing sample of 100 fish was transferred, within a cage, to a
depth of 35 ft in the lake and there suspended for an addit-
ional 24 hr. This depth coincided with the lower portion of
the lake thermocline. At the end of this period the fish were
retrieved and subjected to the standardized decompression test
in Sweitzer Creek water.
The following year this experiment was repeated in a
slightly more elaborate form and with longer periods of holding
at the surface of the lake and at depth. In this experiment
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59
a sample of 400 sockeye smolts was drawn from the migration
in mid-June 0 A sub-sample of 100 of these fish was tested
immediately as a control or index of the mortality associated
with the seasonal effect o The remaining 300 fish were held
three days in lake surface waters, at the end of which time
100 were tested as a measure of the extent of the reversal
of the seasonal effect o The remaining 200 sockeye were then
held at a depth of 35 ft in the lake for a period of seven
days. One hundred of these were then tested for the return
of the seasonal effect. The remaining 100 were held two days
in lake surface conditions and then similarly tested o This study
is illustrated diagramatically in Fig. 36.
Increasing content of dissolved gases o The apparatus
was modified to permit the air saturation of the water in the
chamber to be increased by bubbling air into the chamber under
pressure o In practice, the pressure chamber was filled with
water and air was pumped copiously in through the bottom at
8 psi. The air so entering was allowed to escape through the
small valve at the top of the chamber. Pressure within the
chamber was maintained by the pressure pump and was regu-
lated with the by-pass valve and the air-exit valve. The level
of saturation within the chamber was thus a function of the
initial temperatu!'e and saturation of the water and the dur-
ation of bubbling air thvough under pressure. Temperature
60
and saturation were kept relatively constant at approximately
50°F and 11 ppm and hence it was possible to control gas con-
tent of the water over the range of 100 to 140 per cent of
air saturation by bubbling air into the water for 0 to 60 min.
A nomogram was constructed permitting the duration of aer-
ation to be estimated for any given level of desired saturation.
Nitrogen analyses were conducted on one occasion to
establish whether oxygen and nitrogen were increasing at the
same rate, that is, in relation to the products of their par-
tial pressures and solubilities o Harvey and Smith ( 1961) dem-
onstrated that under pressure these two gases may increase
in solution in relation to their partial pressures alone where
the gas phase is small o Oxygen and nitrogen analyses were
carried out initially and after every 10 min up to 60 min of
aerating under pressure o Four analyses were conducted for
each gas initially and at the end of 60 min and single analyses
at each of the intervening times. The results of this st~dy,
as shown in Table I, indicate the two gases were increasing
in solution at approximately the same rate. The grossest
discrepancy, after 30 min of aerating under pressure, is still
within the limits of the accuracy of the methods of analysis.
In view of this agreement between oxygen and nitrogen satur-
ation, thereafter air saturation within the chamber was deter-
mined solely by the much simpler and speedier Winkler method.
J
1
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TABLE I
Increase in oxygen and nitrogen saturation during
aeration under pressure.
Time in
minutes
0
10
20
30
40
50
60
Oxygen
per cent
saturation
96>.'<
121
129
133
135
136
137*
* averages of four determinations
Nitrogen
per cent
saturation
98*
119
132
137
137
138
138*
61
In operation, a sample of 50 or 100 smelts was placed
in the apparatus, the chamber sealed, filled with water and
air bubbled in at 8 psi for the time appropriate to the desired
level of saturation. At the end of this time the air flow was
stopped, the excess gas bled from the top of the chamber and
the oxygen sample drawn. The pressure was raised to 15 psi
and the fish were held there for some period of time exposed
to the higher gas tensiori of the water. The periods of hold-
ing tested were 5 min, 1, 3, 6, 12, 24 and 48 hr. The
62
ranges of saturation tested were 100 to 110, 110 to 120
and 130 to 140 per cent of air saturation. At the end of the
holding period the fish in the chamber were subjected to the
standardized decompression test.
In these holding experiments, the water in the cham-
ber was static and hence the oxygen in the water was con-
sumed by the fish over a period of 8 to 12 hr. For this
reason the water in the chamber was changed and recharged
every 4 hr. Thus oxygen saturation did not fall below approx-
imately 50 per cent of air saturation; a level which should have
_permitted these fish to maintain blood saturation. (Itazawa,
1959). As before, the fish were held under observation for
r
two weeks following testing. In these saturation experiments,
the series conducted at 100 to 110 per cent of air saturation
served as controls for those conducted at the higher gas
tensions.
Changes in temperature. Before determining the effect
on fish of rapid changes in temperature and hence saturation,
in relation to pressure, it was necessary firstly to measure
the rate of change of temperature of the fish themselves
following a change in the temperature of their environment.
For this purpose, individual sockeye were anesthetized and a
thermistor probe inserted through a small hole near the vent
and located in the region of the head kidney. The lightly-
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63
anesthetized fish were l:h:Jaught to a constant tempe~rature of
45°F, then transferred to 60°F and the temperature record-
ed every 30 sec. The results obtained for five fish ranging
from 3. 8 to 42 g are shown in Fig. 15. With this knowledge
of the rapidity of the change in temperature by the fish, it
was possible to proceed with the temperature studies, allow-
ing only 5 min for the smelts to equilibrate with temperature
of their environment.
Following this, samples of 100 smelts were held at
two temperatures, 45 and 55°F. After two to three d?:ys
of holding at these temperatures the fish were transferred
to the pressure chamber and su~ected to sudden temperatures
increases of 0 to 19°F before being exposed to the standard
pressure test.
Swimbladder gas in relation to pressure
The possibility existed that the gas within the swim-
bladder was responsible in part or in total for the embolism-
induced mortalities observed following pressure reduction. Five
types of experiments were designed to explore this possibility.
Increasing and decreasing gas content of the bladder.
A sample of 50 sockeye smelts was placed in the pressure
apparatus and the fish h~ld 90 min at a pressure of 15 psi.
A large air lock was present in the top of the chamber to
permit the·se fish to inflate their swimbladders to neutral
,_; ..,
% z ..,
a:
% c ...
~ 51
~
~ 50 a: ..,
CL 49 a ..,
,_; 48
47
46
2 3 4
TIME IN MINUTES
e 3.8 orama
o 5.8 orama
~ I 0.0 orama
e 1 7.4 orama
G 42.1 orama
6
64
7
Figure 15. Change of temperature internally of fish transferr~,d
from 45 to 60 o F water.
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65
buoyancy. At the end of the holding time the air lock was
bled off and the chamber completely filled with water P still
at a pressure of 2 atmos. The pressure was reduced grad-
ually and the pressure of neutral buoyancy of the fish noted.
The smolts were then subjected to the standardized decom-
pression test and post-test observation.
This experiment was repeated with a longer period of
holding at a pressure of 30 psi above atmospheric. Even with
a strong flow of water through the chamber the water still
supersaturated appr~ciably o At the end of 24 hr the buoyancy
of the fish was determined and the group subjected to the
decompression test o
A 50-smolt sample was placed in the pressure chamber
and exposed to increasing negative pressures. The pressure
was reduced below atmospheric in increments of 2 o 5 in Hg and
the buoyancy of the fish observed after each reduction. The
vacuum reached 27.5 in Hg at the end of 15 min the pressure
then being returned to atmospheric. These fish then were
subjected to the decompression test.
Bladderless and catheterized-bladder fish. Groups of
20 prickly scuplins ( Cottus as per) were subjected to the same
experimental conditions which had influenced the mortality of
sockeye. Sculpins were acquired from the sockeye migrant
trap in Sweitzer Creek and held in a cage in the stream.
66
A sample of 20 sculpins was placed in the pressure apparatus
and subjected to the standardized decompression test. A
second group of 20 was held 24 hr at a nitrogen tension
elevated to approximately 130 per cent of air saturation. The
excess gas was held in solution by holding the fish and water
at a pressure of 15 psi. As before, the sculpins were then
subjected to the pressure-reduction test. A third group of
20 sculpins was similarly treated but the holding period in the
higher nitrogen tension water was increased to 96 hr to
assure fish-environment equilibrium before decompression.
As a check agaLllst possible species differences between
the bladderless sculpins and sockeye, it was decided to remove
the influence of the sockeye bladder. This was done by in-
serting a catheter into the bladder, as described previously,
such that gas in the bladder was free to escape to the exter-
;
ior. Thus reduction in pressure could not increase the pres-
sure of gas within the bladder and hence increase the diffusion
gradient between the bladder and the remainder of the fish,
nor would the pressure be so great that damage to the blad-
der would result and gas bubbles. enter the blood stream. Both
of these two possibilities were postulated by Jones and
Marshall ( 1953).
Ten such catheterized test fish and ten control smelts
were placed in the pressure apparatus and subjected to a 24
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67
hr exposure to high nitrogen tension { 130 per cent of air
saturation). At the end of this time the fish underwent the
standardized decompression test followed by post-test obser-
vation.
Duct-release pressure and holding sockeye at depth.
The studies on bladderless fish impli.ca ted the swim bladder in
the mortalities associated with pressure reduction and the
experiments on catheterized smelts suggested retention of gas
in the swimbladder was involved in the mechanism of embolism
formation. For this reason the pneumatic ducts of fish held
at the surface of the lake were compared with those of sock-
eye held at a aFe-pth of 40 ft in the lake. These fish were
compared as to the relative patency of the pneumatic duct,
using the method for measuring duct-release pressure as des-
cribed previously. Ten fish held at depth for 7 days were
compared with 10 fish held the same period at atmospheric
pressure in lake water pumped to the surface from depth.
Equilibration of fish with dissolved nitrogen of the environ-
ment
The purpose of this study was to establish the rate
at ·which fish equilibrate internally with the dissolved nitrogen
of their environment. More precisely the rate at which fish
clear excess nitrogen from blood and tissues. The original
approach was to measure nitrogen in venous and arterial
68
blood following transfer of the fish from water of high nitro-
gen to that of a lesser content of dissolved nitrogen. From
a knowledge of cardiac output the rate of nitrogen clearance
could be calculated.
Rate of change of nitrogen in venous and arterial blood.
Adequate blood samples for gas analysis dictated fish of approx-
imately 100 g. For this purpose hatchery rainbow trout,
Salmo gairdneri were chosen. Individual fish were exposed to
increased gas tensions within the pressure apparatus. Nitro-
gen content was raised to 17.5 ml per liter (an average of
127.9 per cent of air saturation, ~ 3.3 per cent for 1 stand-
ard deviation) by bubbling air into the chamber for 30 min at
a pressure of 8 psi. The temperature of the water within
the chamber was held within a few degrees of 57 °F. The
trout were held in this water of increased gas content for
60 min at a pressure of 15 psi above atmospheric. The fish
were then removed quickly from the chamber and transferred
to water of 13.2 ml per liter nitrogen (approximately 100 per
cent of air saturation). Individual fish were held o, 5, 10,
·15, 20, 30 o.r 60 min in air-saturated water and nitrogen in
venous blood was determined at the end of that time. Five
test and 5 control fish were employed for each of the seven
periods of holding.
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69
The absence of arterial blood in the fish :!:teart
required blood be drawn from the dorsal aorta (conducting
oxygenated blood from the gills) if clearance of nitrogen
across the gills was to be measured. Attempts to collect
arterial blood without interfering with respiration, an essen-
tial to the measure of gill clearance, were uniformly unsuc-
cessful. Alternatively the rate was investigated at which
all dissolved nitrogen in the fish was equilibrating with that
of the environment.
Rate a.f'equilibration of total dissolved nitrogen. As
internal nitrogen could not be measured-liirectly, an attempt
was made to measure the nitrogen given up by a fish when
transferred to an environment of lower dissolved nitrogen.
The problem was to measure accurately the nitrogen content
of the medium water, preferably at intervals until fish-water
equilibrium was reached. The nitrogen analysis was consistent
to only +.2 .1 per cent for one standard deviation. This
required that the initial content of dissolved nitrogen in the
water be kept small relative to the nitrogen content of the
fish. This was done by reducing the volume of the water and
lowering the nitrogen concentration by boiling, cooling and
oxygenating the water. In operation, individual yea.rling sock-
eye ranging from 7 to 11 g were acclimated for one week to
water averaging 14.4 ml of nitrogen per liter, then transferred
70
to water averaging 1.64 ml per liter of dissolved nitrogen. ,-,
The shortcoming of this method is unfortunate: the gradient
of nitrogen between fish and environment is several times
greater than that of the blood and pressure studies. vvater
samples were drawn immediately 'the fish were introduced into
the low-nitrogen water and at intervals of 5, 10, 20 and 30
min. It was not possible to keep fish for longer periods
under these test conditions.
Control series, in which only the fish was omitted,
failed to show any change in nitrogen content of the water
in the closed system over the 3 0 min of testing.
The nitrogen lost from·:hhe fish was calculated from
the nitrogen gained by the water, the volume of water being
corrected as each 0.6 ml sample was drawn. At the end of
5 min the nitrogen gained by the water was:
( 4 7 ·1 0 ;0 ° · 6 ) x ( 2.17 -1. 66) = o. 024 ml
where 47.4 is the initial volume of water in ml
0.6 is the volume of the sample drawn at time zero
2.17 is the nitrogen tension in ml per liter at the
end of 5 min
1. 66 is the nitrogen content at time zero
The potential loss of nitrogen was calculated from the
size of the fish and difference between the nitrogen content
of the acclimation water and closed-system water. Without
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71
a precise measure of the solubility of nitrogen in the fluids
and tissues of a fish, the fish were arbitrarily assigned a
nitrogen solubility equal to that of water. Thus-the poten-
tial loss of nitrogen by the fish in this example:
where: 7.5
..1.:..2 x (14.30-2.17) = 0.091 ml
1000
is ,the weight of the fish in g
14.3 0 is the nitrogen content in ml per liter of the
water to which the fish wa'S acclimated
2.17 is the nitrogen tension of the closed-system
water at the end of 5 min
The nitrogen lost by the fish was expressed as per
cent of potential loss at each time interval as an index to
the rate of equilibration of nitrogen between fish and environ-
ment. Thus at the end of 5 min nitrogen loss was:
0. 024 x 100 = 26 per cent of the dissolved nitrogen
0. 091 of the fish.
CHAPTER III
~l
RESULTS
Pressure in Relation to Behavior
The behavioral responses of young sockeye to pressure
were readily apparent. Obvious changes in compensatory swim-
ming and angle of inclination resulted as pressure was increa-
sed above atmospheric e Most apparent was the absence of a
behavioral change with slight increase in pressure ( bu·t apprec-
iable increase in density) e Further increase in pressure soon
evoked maximal compensatory swimming, suggesting young sock-
.
eye have a wide range of preferred density but when this is
exceeded the fish respond maximally. Also noticeable was the
absence of compensatory swimming in fry, its presence in
fingerlings and gradual reduction with increasing size from
one-year to two-year-old smolts.
Response of one-year-old smolts. Ten s.ockeye smolts,
ranging in size -from Z .3 to 6. 4 g were tested. Pectoral fin
rates 1.eanged from 133 to 174 beats per min at atmospheric
pressure (Fig. 16) • This wide range was maintained through-
out the pressures tested. It was due primarily to the size
of the fish, the smaller ·fish showing the more rapid fin
movements. As the pressure was raised from atmospheric
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Figure 16.
50 100 150 200 250 0
PRESSURE IN POUNDS PER .SQUARE INCH
Average and range o~· pf"ctoral fin beats for ten
socke:n~ smelts from atmospheric pressure ~o
psi above atmospheric.
•
73
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CHAPTER IV
DISCUSSION
Young sockeye, unlike other species of Pacific salmon,
spend a year or more in lake residence before migrating sea-
ward. The utilization of the vertical dimension of the lacus--
trine environment requires young sockeye to live over a range
of depths and to make vertical migrations. Pressure is re-
lated directly to depth and is thus an environmental factor in
the lake habitat. Residence and migration over a range of_
--=-=~~pressures present fish with certain physiological problems.
--::-__ ~he nature of these problems and how they are met will be
discussed in the sequence of stages in the life history of the
sockeye salmon.
The problem of pressure stimulating alevins and fry.
Adult sockeye may deposit their eggs in redds on the lake
bottom. This occurs in shallow water at Cultus Lake and at
depths of a hundred feet or more in Great Central Lake,
British Columbia. After hatching, sockeye alevins are sub-
jected to the accompanying hydrostatic pressure until they
emerge as fry from the redd. Experimentally, fry showed no
response to increased pressure prior to initial filling of the
swim bladder. (Fig. 17}. That is, increased pressure does
not result in increased swimming in the fry and probably
75
to 5 psi above atmospheric, equivalent to 10 ft of water
depth, the fish evidenced no change in behavior. Thereafter,
raising the pressure to 10, 15 and 20 psi resulted each time
in an increase in the rate of movement of the pectoral fins.
Concurrently the smelts assumed a progressively steeper angle
(Fig. 5 and 6) from the horizontal reaching approximately 60
degrees at 20 psi. This increased upward swimming permitted
the smelts to maintain a position between the top and bottom
of the pressure chamber. From this central area of the
chamber, individual fish periodically rose to probe the top of
the chamber. Occasionally individuals ceased swimming active-
-=ty and reclined on the bottom of the chamber.
· Compared by means of the t-test, significant differ-
ences did not occur between the fin rates measured for 5 and
10, 10 and 15 or 15 and 20 psi. For example, comparing fin
rates at 5 and 10 psi, t = 1.22 (to.3 = 1.1). Comparing the
combined rates at 0 and 5 psi with those recorded at 10 and
15 psi, the two were significantly di~ferent with t = 3.22
(t 0 • 0025 = 3.17). Again the rates at 10 and 15 psi compared
with those at 20 and 25 psi yielded a t value of
2.91(to.005 = 2.86). Finally, the difference between the min-
imal movements of the pectoral fins at 0 and 5 psi and max-
imal values at 20 and 25 I>si were highly significant with t= 6. 77.
At the end of the test series ""Vvhen the pressure was reduced
. ---------------·-----------------~------------· ----------· ---------·----------~-----·--·-----------------------
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76
from 250 psi to atmospheric conditions, there was a sharp
reduction in swimming activity. Pectoral rates most common-
ly were lower than the initial values, possibly reflecting fatigue.
Comparing intitial and final rates at atmospheric pressure
t = 2.38 {t 0 •05 = 2.26) thus the final rate was slower poss-
ibly significantly, than the initial rate •
Response of fry and fingerlings. Preliminary studies
in 1960 showed a marked difference in the behavior of young
sockeye fry and fingerlings three months of age. The former
showed no increase in pectoral fin movements, no tendency to
swim upward and no increase in swimming activity. The lat-
ter in contrast evidenced the accelerated finning with the pee-
torals which was so characteristic in sockeye smelts. In 1961
this study was repeated commencing with fry dug from the
spawning redds {prior to inflation of the swim bladder) and
replicated at monthly intervals. The results, averages of
five fish of each age are shown in Fig. 17. The change in
behavioral response, as quantified by pectoral rates, was large-
ly completed at the end of one month and at the age of two
months the rather characteristic smelt pattern was established.
Three-, six-and nine-month-old fingerlings showed essentially
the same curves of increasing pectoral fin activity with in-
creasing pressure up to 20 or 25 psi.
77
250
230 NfV'~o-rJ 0 0
210
3 month finterlintt
~ 190 :» z -:1 170 0
a: ...
Q.
Cn 150 0 ... c ..,
CD -----
c !200 9 month fineerllnt• ... ..... o-o-~ 8 :8 ,--_, ~8-o....o-o--O c
~180 6 month fineerline• ... u ...
Q.
110 Jj
afJO
140 I
120
0 50 100 150 200 250 0
PRESSURE IN POUNDS PER SQUARE INCH
Figure 17. Average pectoral fin rat.es of fry and three-, SL"<-
and nine-month-fingerlings.
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78
Response of yearlings and two-year-old smolts o
Sockeye of one and one-half and two years in fresh water
showed a somewhat altered response. The larger fish did not
maintain position in the chamber by simply swimming upward.
These larger individuals instead swam to and fro rapidly along
the long axis of the test cylinder planing upward on the pee-
toral fins o This altered behavioral response is largely respon-
sible for the much more gradual increase in the pectoral fin
(
beats of the two-year-old sockeye o The average pectoral
rates for five fish in each of the two groups are shown in
Fig. 18. The response of these larger fish ( 20 g for the
two-year-olds) suggest sockeye in the oceanic environment
could compensate for negative buoyancy through sustained
swimming.
Pressure in Relation to the Swirrilil-add:e.r
Volume of the bladder. Young sockeye proved to have
a relatively small swim bladder. At neutral buoyancy in fresh
water the swim bladder volume was 5. 96 per cent of the volume
of the fish. Jones and Marshall ( 1953) gave expected values
of 7 per cent for freshwater and 5 per cent for marine tel-
eosts. The sockeye at :J. 96 per cent is intermediate between
these values, perhaps due to the presence of cartilage rather
than denser bony tissue.
"' .....
170
~~o
140
il30
2
a: 120
"' A.
en 110 ..... c
"' CD
! 150 ...
..1
:140
0 ..... u
~ 130
120
110
100
'1''
I ·~
0
0 50 100 150 200 250 0
PRESSURE IN POUNDS PER SQUARE INCH
Figure 18. Average pectoral fin ra tea of eighteen-month and
t v-.ro-:v~·ar-old sockeye.
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Ambient pressure. The method of measuring ambient
pressure was based on Alexander ( 1959a) and for 10 sockeye
smelts yielded an average excess pressure of 0 .z mm Hg o
That the method could not be employed with a high degree of
precision is appar~nt from the variability about the mean»
with .:!:,5o 5 m m Hg for one standard deviation o In dealing with
so low an excess pressure in the swim bladder 9 there was
little or' no separation of the curves of gas expansion. That
is, the curve -for gas confined within the swim bladder and the
curve for that gas outside the swimbladder were very nearly
-identical o · The most extreme individual was chosen (Fig o 8)
·····--to illustrate the measurement of excess presEure o The pur-
pose of measuring excess pressure in the bladder was to make
possible calculation of duct-release pressure o In this regard
the method was sufficiently accurate to show that the pres-
sure within the swimbladder did not exceed appreciably the
external pressure on the fish o
Extensibility of the bladder o The vertical movements
of sockeye and inflation of the swimbladder to neutral buoy-
ancy at some depth below the surface are both related to the
extensibility of the bladder o That is» the ability of sockeye
to move upward to the level of positive buoyancy and undergo
bladder extension rather than gas loss. This could occur both
in the course of vertical movements and possibly during over-
81
inflation of the bladder at the surface to achieve neutral buoy-
ancy at some depth below the surface o For these consider-
ations the statistic sought was the expansion of the. bladder
possible before gas escaped· through the pneumatic duct o Thus
the term extensibility as used here is different from that of
PUexander (1959a).
Ten c antral smelts anesthetized to death and tested
immediately showed an average expansion of 183 per cent
(bladder volume at neutral buoyancy equalling 100 per cent) be-
.£:"-ore gj!JS escaped through the pneumatic duct. The fish ranged
·_· ·_· from 115 to 277 per cent with one standard deviation +62 per
-----cent.
(.
Ten sockeye smelts were provided with an abdominal
slit the length of the body cavity 9 thereby eliminating the con-
fining influence of the abdominal wall. These fish showed, be-
fore gas release, an average expansion of 289 per cent, rang-
ing from 242 to 311 per cent with +20 per cent for one stand-
ard deviation. The body wall thus appears to limit the extent
of bladder expansion to something between doubling and tripling.
In three of these fish the swimbladder ruptured before gas
escaped through the pneumatic duct.
Contractibility of the bladder. Isolated swim bladders
suspended longitudinally in Ringer's solution showed little or no
reduction in length, as interpreted from the kymograph record,
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82
when exposed to adrenaline or acetylcholine ( 10-5). Cross-
sectional loops of bladder similarly tested evidenced a marked
reduction in length when tested with adrenaline or ephedrine
( 10-5 ) • The shortening of the loop of bladder was one-
quarter to one-third of its length, approximately equal to a
one-haff reduction in the cross-sectional area of the lumen of
the swim bladder. Considering the sockeye swim bladder to be
a cylindrical figure, the gas expulsion accompanying a contrac-
tion of this magnitude would be one-half or more of the
volume at neutral buoyancy.
Such loops exposed to 11 dibenzyline" ( 10-5) evidenced
a gradual relaxation and could not be stimulated to contract
with adrenaline or ephedrine. The 11 dibenzyline 11 blockade could
not be by-passed with monoacetin over the range of concen-
trations 1o-5 to 10-3. In non-blocked loops of swimbladder
adrenaline-induced contraction was relatively slow, lasting 2
to 3 min, in contrast to loss of gas on sounding which was
complete usually within 1/2 min.
Little or no response accompanied treatment of isol-
ated loops with acetylcholine, piloce1rpine or atropine ( 10-5).
This suggests parasympathetic control was not involved in the
contraction of the bladder and hence the expulsion of gas from
the swimbladder.
•
l
83
Gas secretion o Fish held above the screens in the 7 5-
liter tanks returned to the surface within a few minutes after
sounding and commenced gulping atmospheric air o The density c-l
of these fish was very close to neutral buoyancy during the
course of the eight-day experiment {Fig. 19} o Fish held
below the screens continued to lose gas from the swimbladder
with the density of the fish increasing over the period of
8 days o There was thus no evidence of inflation of the swim-
bladder by means of gases dissolved in the holding water.
Fish held under pressure fo 24 hr similarly failed to
~··· _ _=:jp.crease the volume of gas in the swim bladder. In the first
..... test three smolts showed an average density increase of 0. 005
g per ml and in the second an average increase of 0 o 007 g per
ml. Thus holding sockeye smelts under pressure for 24 hr
did not result in the addition of gas to the swim bladder, on
the contrary there occurred a slight gas loss as evidenced by
an increase in density.
Loss of gas on· sounding. Sixty sockeye smelts held 2
days in water 50 em deep showed a mean density of 0. 9995 g
per ml with ,:tO. 0009 g per mL for one standard deviation.
Fish similarly held, but startled into sounding by disturbance
on the water surface, showed a mean density of 1. 0143 g per
ml with +0.0086 for one standard deviation. This was an
average loss of 23 per cent of the gas from the swimbladder
·----------
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84
below ICfHft
-
above acrttn
--~~----TIME IN DAYS
Figure 19. Density of sockeye smelts held above and below
screens. Range shown by vert :cal bar, mean by
long horizorit~al and one standard deviation by" short
horizontal bars.
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85
gas on sounding o Smelts induced to sound wildly in an agitated
glass cylinder had a mean density of 1 o 0244 g per ml with
.:!:,0 o 0090 for one standard deviation. This was an average loss
of gas £rom the swim bladder of 38 per cent o The greatest
loss of gas by any fish was 72 per cent o In the drug-eval-
uation studies 1 referred to below, 720 control smelts sounded
to a mean density of 1. 0214 g per ml, an average loss of gas
of 34 per cent.
Sockeye salmon smelts held in a solution of the sympa-
thomimetic ephedrine evidenced the same sounding response as
control fish when tested. However, significantly more gas
was lost from the swim bladder on sounding o The fish in the
two series of tests with exposure to 100 mg per liter of
ephedrine, sounded to a mean density of 1. 0280 g per ml
(Fig. 20), an average loss of gas of 44 per cent. The density
or gas loss of ephedrine treated and control fish differed sig-
nificantly, with t-test values of 3.93 and 2.92 (to.0025=2.91).
The density of smelts held in 200 mg per liter of ephedrine
before testing, differed even more from the control fish on
sounding with t values of 5.60 and 7.22 for the two series.
That loss of gas on sounding was enhanced by adrenergic stim-
ulation suggests the drug ephedrine was acting to lower the
threshold of response.
Ephedrine ·.treated sockeye showed marked blanching
t( 'l
'
86
1.0~
0
0
0 0
0 •o
1.04 0 00 ' -,
0 0
a: 0 0
w 0 • 0 .... 0 000 • • w
~ • 0 0 -~ • • 000 .... oAo 00 z .0 0 • oo•oo g:g w 1.03 1-8 u 0 X T 00 A
0 u • •o 0~ .o ~ CD • • • 0
::) A 00 0 00 •o• •o 0 eo u oo•oeo o•~ 0 y
a: •
~ 1.02
eo ... .... .. ...0
1-0 I 00 ooeo ... eo• ••
Cl) 0 •o • "-•• .... .... eo
c· ~ 0 eo• •• ".-.r
c o•o oeoe • ... • a:
" ~·. •o ·-.. • • z .o• .. • -1.01 ~ ... ,.. .... •
Cl) • • z 0 w
Q
1.00 -o -experimental
•-cantral
0 9 r I I I I I I I I I I 1 . 9~--L---L---~--~--~--~--L---L---~--~---~--~~
0 I 2 3 4 ~ 6 7 8 9 10 II 12 13
TIME. IN HOURS
Figure 20. Density of sockeye smolta on ao.undlng. Teat fish
ex·posed to 100 mg per liter of ephedrine for up to
12 hours.
•
~-1
l ,,
'I
~ ~J
cl
' 1
' 1
:-]
J
-~{#~ ('•'
J
: I
]
J
~ J
,J
J '-·· '
J
:J
87
of the chromatophores after, one-half to one hour of exposure.
In the first 11 dibenzyline 11 series, the densities of test
and control groups did not differ significantly during the initial
2 hr of drug exposure, with t = 0.67 (t 0 •5 = 0.69). Beyond
2 :hr.· of holding in 11 dibenzyline 11 , gas loss on sounding declined
rapidly until after 4 hr treatment no loss of gas was observed
on sounding. The density difference between treated and con-
trol fish was highly significant with t = 12 o10. The sounding
response was unaltered except for the failure of gas to escape
from the swim bladder. The study was replicated at the same
dose of 5 mg per liter and in the second series loss of gas
was retarded even in the one-and two-hour treated groups.
The combined results appear in Fig o 21o
A marked chromatophore response was apparent follow-
ing 1 to 2 hr of exposure to 11 dibenzyline" with the fish becom-
ing noticeably darker.
The adrenergic blocking agent 11 hydergine 11 also resulted
in significantly less gas being los-t on sounding among treated
.. fish than in the corresponding controls; comparing densities
t = 3. 87 (to. 0025 = 2. 91) o At the tested dose of 10 mg per
liter, a chromatophore response was apparent following 3 to
4 hr of exposure.
Cholinergic stimulating and blocking agents yielded less
consistent results than the adrenergic drugs described above.
\'~ ·~
88 <r ~~
1.0~
o -eaperimentol
0 •-control
:1 1.04 1-• I
c '1 ....
~ • ....
2 • • 1 ~ • z wi.03 1-• 0 0 • eo • •• • 0 J. -I • • CD • 8 ::::> 6 A • • 0 t • • • •• c 8 I • ~ 1.02 ~ I • I. I ., A \ en 0 • • 2 eoe I • .,
c ' -r I • a:
o¥-• ~ C) • I • ""' z • • .. • -1.0 I ~ eooe • 0
> 0 §
~ 0 • -; I en § 0 z 0 .... 0 00 00 0 a 0 + 1.00~ cr i Jo 0~~
88
0.99 I I I I I I I I I I I I
0 2 3 4 ~ 6 7 8 9 10 II 12 13
--------~---·-· TIM£ IN HOURS .l
Figure 21. Density of sockeye smelts on sounding • Test
fish exposed to 5 mg per liter of "dibenzyline".
j G ! -
I
I
• I
I
I
I
.J
-1
J
89
Smelts held in 100 mg per liter of pilocarpine lost 42 per cent
of their swim bladder gas on sounding, significantly ( t = 2. 76,
to. 005 = 2. 66) more than the 36 per cent lost by the corres-
pending control fish. Fish treated with atropine at a concen-
tration of 200 mg per liter lost only 29 per cent of swim-
1 bladder gas on sounding, significantly ( t = 4.12, to. 0025 = 2. 97}
.l less than the 38 per cent of the corresponding controls. In
contrast the cholinergic blocking agent 11 darbid 11 did not alter
] significantly loss of gas on sounding.
Gulping atmospheric air. Smelts catheterized and then
--held in 11 dibenzyline 11 solution ( 4 hr at 5 mg per liter) continued
to surface, mouth air and pass the gas into the swim bladder.
There was thus no evidence that this drug was influencing the
ability of the fish to inflate their swimbladders with atmos-
pheric air. This was confirmed on non-operated fish which
I
. J
were induced to sound, occluded from the water surface by
means of a screen and in this partly degassed condition exposed
to "dibenzyline" for 4 hr. On removing the screen at the end
of this time, treated and control fish prompty returned to the
surface and inflated their sWim bladders to neutral buoyancy.
Catheterized smelts treated with atropine similarly con-
tinued to attempt to complete inflation of the swim bladder. As
was the case with "dibenzyline", atropine did not interfere with
the process of air passing into the swim bladder. The response
90
however was visibly slower in the atropine treated as compared
to the control fish o
Duct-release pressure o During the course of the stud-
ies on the pressure necessary to affect release of gas through
the pneumatic duct, three control series were conducted with
ten fish in each. These series showed average pressures at
release of 28 o 9, 28 o 6 and 26 o 9 mm Hg and .did not differ sig-
nificantly o Smelts tested at intervals after death showed a
progressive reduction in duct-release pressure up to 3 0 min.
A regression line of Y = 27 o 18-0 o 78X was calculated for this
time period {Fig. 22) o Fish tested over the period of 5 to
30 min after death differed significantly from control fish at
time zero, with t =4.15 {t 0 •0025 =3.50). Beyond 30 min
after death, duct-release pressure increased rapidly and in
3 fish exceeded that of the controls. This increase in duct-
release pressure coincided with the onset of rigor.
Ten smelts exposed to "dibenzyline", for the time and
concentration effective in stopping loss of gas on sounding,
showed a mean duct-release pressure of 26.8 mm Hg and did
not differ significantly from the control groups. Ten smelts
held in a solution of 100 mg per liter of atropine for 12 hr
showed an average duct-release pressure of 0. 2 mm Hg.
Atropine treated fish differed significantly from control and
"dibenzyline" fish with t = 5.32 {to.0025 = 3.69).
rj
J
J
']
J
J
0
%
E
E
60
50
z 40
"' a:
~::) en en
w 30 a:
A.
w en c
~ 20 w a: ... u
::)
0 10
0
91
·o
0
-10 ~--~----~--~--~----~--~----L----L--~~--~--~~~
0 10 20 30 40 50 60
TIME IN MINUTES
Figure 22. Change ln pressure req-.dred to force gas out
through the pneumatic duct following the death
of the animal.
•
92
Histological examination o The pneumatic duct proved to
be a convoluted connection between oesophagus and the anterior
end of the swim bladder. This is apparent in Fig. 23, the
oesophagus, lower left, connecting to the swim bladder, upper
right. In the upper photomicrograph of Fig. 23, the connec-
tion cannot be traced due to the lateral curvature of the
duct and the duct appears to terminate in an oesophageal bulb o
In the lower photomicrograph the lumen of the duct may be
traced from bulb to anterior swim bladder. No obvious sphinc-
ter is apparent but the musculature of the oesophagus could
conceivably function in this way.
The pneumatic ducts were examined from smelts
treated with sympathomimetic and parasympathomimetic drugs
plus adrenergic and cholinergic blocking agents. Drug doses
~ffective in altering the loss of gas on sounding had no visible
affect on the pneumatic duct o Sockeye injected with 0.1 mg
of acetylcholine, however, evidenced a marked constriction of
the duct and bulb lumen. Fish injected with atropine showed
the more or less typical lumen as illustrated.
Pressure in Relation to Gases
Limnological investigations
The freshwater environment, such as Cultus Lake,
presents certain problems to the vertical movements of young
~~
~··~·
~-l
J
~ J
, I
c J
]
J
-.i····· J~J
-1
J
J
1
' 1
J
c,J \w
J
J
93
Figure 23. Photomicr·oGraphs of the pneumatic duct nf
the sockeye s:nolt. Lumen of the dt!ct may
be traced from oesophagus through bulbs and
thence to anterior end of swlmbladdcr •
. ,
94
sockeye. One of these is the problem of internal supersatur-
ation accompanying temperature increase and decompression.
The definition of the temperature and gas content of the
lacustrine environment thus became an integral part of the
study of the pressure problems of young sockeye~ Contin-
uous limnological investigation was limited to the calendar year
1961, the results of which are presented below.
Temperature. During the winter of 1960-61 Cultus
Lake remained free of ice and cooled to a minimum temperature
of 41°F in late February (Table II, Fig. 24). Considerable
---heating and mixing took place before thermal stratification,
with bottom temperatures reaching 43. 8°F and surface tern-
peratures 46°F in late April. Stratification was established
by mid-May and surface heating continued into August. Dur-
ing the period May to August there was warming to deeper
layers. At 40 ft the temperature increased 7 °F to 53 op
with only partial loss of the excess gas. From August to
mid-September the temperature at 40 ft increased an addit-
ional 6.5°F to 59.5°F, due in part to downward mixing of
warmer water. Cooling and downward mixing continued from
August to December. Complete turnover was achieved in
early December as evidenced by isothermal conditions and the
( sudden increase in oxygen at a depth of 130 ft.
--]
cl 95
TABLE II
~ I Temperature in degrees Fahrenheit
,-1 of Cul tus Lake , 1961
l Depth Jan. Feb. Mar. Apr. Apr.
in ft. 27 24 17 6 26
: 1 0 42.8 41.0 41.9 45.5 46.9
5 42.8 41.5 -41.9 45.0 46.9
l 10 42.8 41.5 41.9 44.4 46.9
15 42.8 41.5 41.9 44.2 46.9
20 42.8 41.5 41.8 43.2 46.8 cl 25 42.8 41.5 41.7 42.9 46.5
30 42.8 41.5 41.7 42.9 46.3
40 42.8 41.5 41.7 42.8 46.0
J 50 42.8 41.5 41.7 42.5 45.9
130 42.8 41.5 41.5 41.8 43.8
J Depth May. June June June July
17 1 13 30 18
J
0 56.5 65.3 69.5 69.0 72.3
J 5 53 .o 60.0 63.5 66.2 72.0
10 52.5 58.0 63 .o 65.5 71.0
15 49.8 55.0 62.5 65.1 69.5
I 20 49.0 53.0 60.0 63.0 68.0
25 47.7 50.0 55.0 57.5 64.0
30 47.2 48.0 52.0 54.0 6o.o
~ l -~·------40 46.3 46.0 48.5 50.0 53 .o
50 45.5 45.0 46.5 47.0 48.0
130 43.5 43.4 43.6 42.2 42.3
J
},c:~.
L_\!j~;i
J
J
96
TABLE II (continued}
Depth Aug. Sept. Sept. Oct. Oct.
in ft. 4 7 18 8 24
0 73 .o 66.9 65.9 58.5 54.0
5 73 .o 66.7 65.8 58.5 54.0
10 73.0 66.5 65.7 58.5 53.9
15 72.5 66.5 65.6 58.5 53.9
20 71.0 66.5 65.5 58.5 53.9
25 65.0 66.5 65.4 58.4 53.9
30 63 .o 65.5 65.3 58.4 53.9
40 53 .o 56.0 59.5 58.1 53.9
50 .48.0 50.6 51.0 51.4 53.8
130 42.3 44.0 44.2 43.8 43.6
:
Depth Nov. Nov. Dec. Jan. Jan.
in ft. 9 24 11 4/62 25/62
0 49 .. 6 46.4 44.2 42.6 40.5
5 49.6 46.4 44.2 42.6 40.4
10 49.6 46.4 44.2 42 .. 6 40.3
15 49.6 46.4 44.2 42.6 40.2
20 49.6 46.4 44.2 42.6 40.1
25 49.6 46.4 44.2 42.6 40.0
30 49.6 46.4 44.2 42.6 40.0
40 49.6 46.4 44.2 42.6 40.0
50 49.6 46.4 44.2 42.6 40.0
130 44.8 45.8 44.2 42.6 40.2
-J
-~-~
'~ .,
~ "j
~ l
: l
~ l
J
]
-~~
-I
. -1
1
: I
. 1
: J
r . \ .··• '~
. )
: I
97
0
10
30
40 45 50 55 60 65 70
TEMPERATURE IN DEGREES FAHRENHEIT
Figure 24. Temperature of the upper SO feet of ·Cultus Lake
during 1961.
•
Depth May June June June July
in ft. 17 1 13 30 18
0 11.6 10.0 9.8 9.7 9.0
5 12.0 10.3 10.1 9.5 9.1
10 12.1 10.7 10.2 9.6 9.1
15 12.3 11.5 10.3 9.6 9.2
20 12.7 12.0 10.5 11.2 9.3
25 12.6 12.6 12.5 12.6 10.5
30 12.4 12.3 12.6 12.8 12.6
40 12.0 11.7 12.0 12.3 12.4
50 11.6 11.1 11.2 12.2 11.9
130 10.8 8.5 9.4 9.4 9.3
l
-] 99 .,..· ... .(ti
" TABLE III (continued)
~ 1
~-l Depth Aug. Sept. Sept. Oct. Oct.
in ft. 4 7 18 8 24
~ I 0 8.9 9.6 9.7 10.0 10.2
5 .8.8 9.6 .9.6 10.1 10.3
: j 10 8.8 9.5 9.6 10.3 10.5
15 8.9 9.4 9.7 f0.1 10.4
20 9.8 9.4 9.6 10.2 10.4
J 25 11.6 9.6 9.8 10.2 10.5
30 12.4 10.0 11.3 10.o2 10.5
40 12.6 12.6 12.0 11.1 10.4
J 50 11 .. 7-12.0 10.5 9.8 10.0
130 10.1 8.1 .5.3 7.5 7.9
: 1
Depth Nov. Nov. Dec. Jan. Jan.
~ l in ft. 9 24 11 4/62 25/62
.J 0 10.4 10.0 10.7 11.5 12.2
5 10.5 9.7 10.9 11.5 12.3
10 10.4 9.8 10.7 11.4 12.1
:J 15 9.7 9.6 10.6 11.2 12.0
20 .9.8 9.6 10.6 11.2 12 .• 1
25 10.1 9.7 10.6 11.4 12 .• 1
1
30 10.3 9.7 10.6 11.2 12.2
40 10.3 9.7 10.6 11.2 12.2
50 9.8 9.7 10.5 11.2 12.2
: j
130 7.4 6.6 10.6 11.1 12.0
J
].:.
' '"--'. :·'
J
J
100
TABLE IV
Oxygen expressed as per cent of air saturation
Depth Jan. Feb. Mar. . Aprg Apr.
in ft. 27 24 17 6 26
0 93 93 95 100 101
5 93 93 93 101 101
10 92 93 94 101 101
15 92 93 95 100 102
20 91 93 94 99 101
25 92 93 94 98 100
30 92 93 94 97 99
40 93 93 93 96 98
50 94 92 94 95 98
130 95 91 93 75 82
@j .
Depth May June June June July
in ft. 17 1 13 30 18
0 110 106 109 107 103
5 110 103 105 102 104
10 110 105 106 102 103
15 108 108 106 102 102
20 110 110 105 116 102
25 108 111 117 122 110
30 105 106 114 118 126
40 100 97 104 108 114
50 95 92 95 95 102
130 88 69 76 75 74
~-l
~-1 101
~ J TABLE IV (continued)
~-1 Depth Aug. Sept. Sept. Oct. Oct.
in ft. 4 7 18 8 24
: I 0 102 104 104 98 95
: 1
5 101 103 102 99 96
10 101 102 102 101 98
15 102 101 101 99 97
: I 20 111 101 102 100 97
25 122 103 104 100 98
30 127 107 120 100 98
] 40 115 119 118 109 97
50 100 106 94 88 93
130 81 66 43 61 64
]
·.;.<~~ ]~
' 1 Depth Nov. Nov. Dec. Jan. Jan.
in ft. 9 24 11 4/62 25/62
J 0 92 85 88 92 94
5 93 82 89 92 95
1
10 92 83 88 91 93
15 85 81 87 90 92
20 86 81 87 90 93
1
25 89 82 87 91 93
30 91 82 87 90 94
40 91 82 87 90 94
~ j
50 86 82 86 90 94
130 65 55 87 89 93
J
1~ · .. '/ ,, ...
J
:J
-~1
I
"l
c j
-l
lOZ I
"l
~ i
10 I
~ i
30
c
20
30
40
50
9 10 II 12 13
OXYGEN IN MILLIGRAMS PER LITER ( P. P.M.)
Figure Z5. Dissolved oxygen content in milligrams pe~ liter,
Cul tus Lake , 1961 •
•
-,
-1 _·
l ( J
~ !
·~ -]
l
-1
I '
]
' 1
.J
jC
1 J.,
J
l
... \
J
J
' ]
j
:~
""-
J
. J
0
30
~ --o
ca. w
0
80 90 100 110
OXYGEN PER CENT SATURATION
Figure 26. Oxygen content expressed as per cent of air
saturation at surface pr·~ssure ard temperature
in situ.
•
103
IY, \::]
Ei&
(·-,~. ····:'
.::.#
TABLE v
Oxygen expressed as per cent of air saturation
at surface temperature
Depth Jan. Feb. Mar. Apr. Apr.·
in ft. 27 24 17 6 26
0 93 93 95 100 101
5 93 93 93 101 101
10 92 92 94 102 101
15 92 93 95 101 102
20 91 93 94 101 101
25 92 93 95 100 101
30 92 93 95 99 100
40 93 92 93 99 100
50 92 91 94 99 100
130 95 91 93 75 82
Depth May June June June July
in ft. 17 1 13 30 18
0 110 106 109 107 103
5 114 110 112 105 105
10 115 114 113 106 105
15 117 121 115 106 106
20 121 127 117 124 107
25 120 133 138 139 121
30 118 130 139 141 144
40 114 123 132 135 143
50 110 118 125 124 136
130 88 69 76 75 74
104
l
~~~,
l
l
~ 1
~J
'j
]
J
·:fB
J
~l
J
J
: 1
j
J -~
~'--'
J
J
Depth
in ft.
0
5
10
15
20
25
30
40
50
130
Depth
in ft.
0
5
10
15
20
25
30
40
50
130
TABLE · V {continued)
Aug.
4
1.02
101
101
102
113
133
142
144
134
81
Nov.
9
92
93
92
85
86
89
91
91
86
65
Sept.
7
104
104
103
i.02
102
104
108
135
129
66
Nov.
24
85
82
83
81
81
82
82
82
82
55
Sept.
18
104
102
102
104
1.02
105
121
127
112
43
Dec.
11
88
89
88
87
87
87
87
87
86
87
Oct.
8
98
99
101
99
100
1-00
100
109
96
61
Jan.
4/62
92
92
90
89
89
90
89
89
89
89
Oct.
24
95
96
98
97
97
98
98
97
93
64
Jan.
25/62
94
95
93
93
93
93
94
94
94
92
105
c
30
40
80
JviJ II
#''ril2e
n-Aprile
IT
I //J
o o yo/
00 I 1/ 0
'r I ••••••
\ 0ct z4f \ I/
o Oct8o o~ o~ '
\ . ~ -------\ yo~ o~
0 0 ! ~~ ~ 0 I I ·~ /!/0
90 100 110 120 130 140
OXYGEN PER CENT SATURATION
1co
ISO
Figure 27. Oxygen expressed as per cent of air saturation at
·-·····-·---·· --
surface temperature and pressure.
•
~]
c l
~ 1
' l
~ 1
1
: 1
]
~ 1
]
' J
~ 1
J
I
: j
J
L::;
J
J
Depth
in ft.
0
5
10
15
20
25
30
40
50
130
0
5
10
15
20
25
30
40
50
130
TABLE VI
Dissolved nitrogen content, per cent of air
saturation and per cent of air saturation
at surface temperature
Apr. May June June July Sept. Nov.
6 17 13 30 18 18 9
Nitrogen in milligrams per liter
18.9 17.7 15.8 14.9 14.6 15.3 18.4
20.0 18.7 15.9 15.0 14.5 15.2 18.4
19.6 18.7 16.2 15.0 14.5 15.5
20.0 18.8 16.2 15.6 14.8 15.5 17.9
19.9 19.4 17.9 15.6 15.0 15.2 18.2
19.2 18.9 17.9 16.3 15.9 18.2
20.0 20.0 19.4 19.1 18.5 17.8 18.4
20.0 19.4 19.7 19.3 !9.0 19.3 18 .. 8
2-0.0 20.1. 19.7 19.1 19.4 19.6 18.3
19.4 20.4 19.8 20.1 19.7 20.1 19.5
Nttrogen as per cent of saturation
98 105 107 101 103 100 101
103 107 102 99 101 100 101
100 106 . 103 98 100 101
102 103 103 101 101 101 98
100 105 105 99 101 100 100
102 111 108 105 104 100
101 106 109 110 114 116 101
101 102 106 106 108 118 103
100 104 104 101 104 110 100
96 103 100 100 98 100 100
107
Jan.
25/62
20.3
19.8
19.8
20.0
20.2
20.1
20.3
Z-0.1
20.5
19.5
99
96
96
97
98
97
98
97
99
94
108
TABLE VI (continued)
Depth Apr. May June June July Sept. Nov. Jan.
in ft. 6 17 13 30 18 18 9 25/62
Nitrogen as pei.r cent of saturation at surface temperature
0 98 105 107 101 103 100 101 99
5 104 111 108 102 102 1-00 101 96
10 102 111 110 102 102 102 96
15 104 112 110 105 1-04 1-02 98 97
20 104 115 115 106 105 100 100 98
25 114 129 121 114 104 100 97
30 104 119 132 129 130 117 101 98
40 104 116 134 131 134 126 103 98
50 104 119 134 130 136 129 100 100
130 101 121 134 136 138 132 107 95
~
~~ ~i9J ..:.~·-
Oxygen content and saturation. In early January of
1961, dissolved oxygen was 11.2 mg per liter or app-roximately
90 per cent of air saturation (Table III and IV, Fig. 25 and ~ ... v
26). Dissolved oxygen continued to increase until early April,
beyond which surface oxygen declined and the absolute level
of oxygen in the thermocline increased. Oxygen saturation in
the region o:£:.the )thermocline increased both through heating
of water in situ and through oxygen produced. The excess
gas was present below the zone of mixing and was retained
in solution by the hydrostatic pressure. By September,
oxygen tension at 50 ft ·was below the April maximum values
and saturation below 100 per cent in spite of slight warming.
---1
rl
~ J(Jt
l
~l
]
~ I
~ l
'l ,_
n
11
~J
J
J
L J
~ J
J
.1,;-~
"\ .. --:.;
J
J
109
Autumn and winter cooling and mixing reduced oxygen satur-
ation to a minimum of 82 per cent in late November. There-
after oxygen uptake exceeded the rate of cooling and relative
saturation increased.
In the section devoted to the vertical movement of
fish, sockeye migration will be discussed in relation to rel-
ative temperature and saturation changes. For this reason
oxygen saturation is expressed also as per cent of saturation
at surface temperature and pressure (Table V, Fig. 27).
Nitrogen content and saturation. In late January,
nitrogen content was approximately 20 mg per liter or 97
per cent of air saturation (Table VI, Fig. 28 and 29). By
early April no net change had taken place in the nitrogen
tension of the water but increasing temperature had raised
the saturation to 100 per cent. Sui'face water saturation
exceeded 100 per cent briefly April to June. At depths of
30 to 50 ft, temperature increased markedly May to Septem-
ber while nitrogen content declined little and hence the rel-
ative saturation was increased considerably above 100 per cent.
Cooling and mixing of lake water did not lower nitrogen sat-
uration as drastically as that of oxygen, with nitrogen satur-
ation at approximately 100 per cent during incomplete mixing
in November. As in the case of oxygen, nitrogen has been
calculated also as per cent of saturation of surface temper-
a ture and pressure (Fig. 3 0 ) •
(
% () ...
Q.
"' a
10
20
30
40
50
110
~~--~--~---L--~--~--~--~~~~--~---L--~--~--~~
13 14 15 16 17 18 19 20 21
NITROGEN IN MILLIGRAMS PER LITER ( P. P.M.)
Figure 28. 0issolved nitrogen content in milligrams p~r liter
Cultus Lake, 1961.
•
.~-:
1
~l c~~
' l
cl
~ I
J
' \
0
10
20
30
40
~ .., .., ...
z50 -z 0 =: ... a
10
20
30
40
111
95 I 00 I 0 5 II 0 115 120
NITROGEN PER CENT SATURATI9N
Figure 29. Nitrogen content expressed as per cent of air
saturat~n at surface pressure and temperature
in situ. --
•
( ..
C.
0
10
20
30
40
10
20
30
40
so
90
112
100 110 120 130 140
NITROGEN PER CENT SATURATION
Figure 30. Nitrogen expressed as per cent of air saturation
at surface temperature and pressure •
•
~~
I
c I
" l
~ 1
' l
J
: J
cf~
113
Tolerance to pressure and resistance to decompression
By no means all of the 143 tests of 1959 and 117
tests of 1960 were concluded successfully. Sudden, severe
flooding of holding boxes in 1959 resulted in the loss of one
series of experiments. A second complete series was lost
in 1960 as a result of copper sulfate treatment of the near-
by lake-shore. Finally, smelts held in Sweitzer Creek at
high temperatures were prone to disease and in both 1959
and 1960 studies on tolerance to pressure were terminated
prematurely for this reason.
During the course of the studies on resistance to
decompression, a total of Z, 800 control fish consisting of four
groups of 300 each and eight groups of ZOO fish were used.
Mortality among these control fish ranged from 0 to 1 per
cent per week and averaged 0.45 per cent per week during
the Z weeks of post-test observation.
Magnitude of positive and negative pressure. Sockeye
smelts exposed to positive pressures as high as 300 psi evi-
I denced little or no·.·apparent ill effects. Samples of smelts
raised to 300 psi and returned to atmospheric pressure evi-
denced mortalities of 0 to 1 per cent per week (Fig. 31 and
32), during post-test observation and hence were indistinguish-
able from the mortality rates of the control groups.
The effects of negative pressures on sockeye smelts
114
varied seasonally and are discussed further in a separate sec-
tion. During the bulk of the studies, conducted from late
March to early May, exposure to negative pressure resulted in
a mortality which increased with increasing vacuum (Fig. 31
and 32). Groups of smelts were exposed suddenly to vacuum
conditions from atmospheric, 50 psi and 300 psi above atmos-
pheric pressure. The magnitude of the positive pressure had
little or no effect on the resulting mortality. The two test
series showed similar slopes ( 0. 058 and 0. 073) and intercepts
( 0. 81 and 0. 41) • At pressures greater than 5 in Hg of vo.c. ..
vacuum (absolute pressure 633 mm Hg) :.:<.mortalities were of
the same order of magnitude as the control group&.
Duration of positive and negative pressure. As ex-
plained under methods, the apparatus would not permit the
maintenance of high pressures for long periods of time. Smelts
exposed to 50 psi for 24 hr then returned to atmospheric con-
ditions evidenced 0. 5 per cent per week mortality during post-
test observation. Similarly goups of smelts held for 7 days
at a depth of 40 ft in the lake ( 18 psi) showed no adverse
effects when examined on return to atmospheric conditions.
Duration of exposure to negative pressure was inves-
tigated at a vacuum of 10 in Hg ( 506 mm Hg absolute pres-
sure} and periods of 0.1 to 100 sec. This series was term-
inated on the appearance of disease-induced mortalities in some
l
, I
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. -,
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l
-J
'1
1
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]·
115
of the groups. During the initial perio.d of post-test obser-
vation, prior to the onset of the disease, there was no indi-
cation of any difference in the mortality rate among the test
groups. Similarly, smolts gradually exposed to a reduction in
pressure below atmospheric showed no ill effects immediately
apparent at vacuum conditions of 20 to 25 in Hg ( 125 mm Hg
absolute pressure). This was true only if the rate of reduc-
tion of pressure and hence expansion of gas did not exceed the
rate at which the fish expelled gas from the swim bladder.
Vacuum conditions were not maintained sufficiently long to
reduce oxygen tension to the lethal level.
Rate of increase and decrease in pressure. Pressure
was routinely increased at the rate of 1 psi per sec apparently
without ill effect on the fish. The most rapid rate of pres-
sure increase tested was 10 psi per sec which is the equiv-
alent to a descent through water at the rate of 20 ft per
sec and this also was without adverse effect.
The effect of the rate of reduction of pressure w~s
tested over the range of 1. 5 to 7, 500 psi per sec. Two ser-
ies were conducted in 1959 and 1960 in which groups of 200
smolts were lowered from 300 psi to atmospheric conditions.
The results are sho.:wn in Fig. 33. There is some suggestion
of slightly higher mortalities at the most rapid rate of
c
4
>-~
..13 c ~ a:
0 -2
!E ...,
u
G:2 ...,
Q.
•
•
X
X
• 19~9
0 1960
control meon
(+) 0 (-) 10 20
PRESSURE IN INCHES OF MERCURY
116
•
•
30
Figure 31. Mortality per week following decompression from
50 psi to positive ar:d negative pressure.
•
c 1
c j
J
:: lc.
J
' ' . ]
c ~
1
' J
i l
: 1
''
I L J
·J
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11'
5~------------------------------------------------.
4
0
0 •
• 1959
01960
~2
a:
"' A.
X
X
•
0
X
OL---~~~~--0----o-OOL-------L-------L-------L-~--c-on~tr_o_l __ ~ __ on~----~
10 (+) 0 (-) 10 20 30
PRESSURE IN INCHES OF MERCURY
Figure 32. Mortality p€:r week following decompression from
300 psi to positive and negative pressure. ·
•
>-...
..J c ... a::
0
:1 ... z
"' u
a::
"' ~
118
1.25 ~-----------------------------.
1.00 ~
0.75 ------···· ..
0.50 -X 0
0.25 ~
•
0
0 X
X • 1959
0-1960
X
control mean
0
X
0
0~--------------L-'--------------L---------------L-·------------~
I 10 I 00 1,000 10,000
RATE. OF PRESSURE REDUCTION IN P. S.l. PER SECOND
Figure 33. M.ortality per week accompanying various rates
of reduct~n of pressure.
'.
l
c J
J
J
1
1
~ J
J
J_,
'---~-::-
J
J
decrease in pressure, but the maximum mortality of 1 per cent
per week is within the extreme range of the control mortal-
ities.
It should be noted the above series of tests were con-
ducted on smelts migrating from Cultus Lake early in the sea-
son (late March to early May). Decompression tests yielded
consistently low mortalities during this period, in contrast to
the increasing mortalities late in the season (late May to late
June), as described below.
st:tonditions altering resistance to decompression
Seasonal effect. The relatively small proportion of mor-
talities and injuries resulting from decompression changed sud-
denly during the course of the season. This change coincided
with a temperature of 51 °F in Sweitzer Creek, occurring
about mid-May and coincident with the termal stratification of
Cultus Lake. Among smelts tested migrating from the lake,
the mortality increased rapidly with increasing temperature as
shown in Fig. 34. The smelts died inside the pressure cham-
ber within a few minutes of being exposed to a sudden reduc-
tion in pressure below atmospheric conditions. In the fish
examined, death was due to minute gas emboli most commonly
• lodged in ithe heart or ventral aorta. This phenomenon was
first observed during the studies of the spring of 1959.
•' 120
50~------------------------------------------~--~_,
APRIL-JUNE 1959
40 -0
0
>-0 ...
:;j
c 30 '"'" ... a:
0
2 0 ... z --.... ---
c u
a: 20 '"'" 0 ·r-"' 0..
0 0
0
0 0
I 0 1-0
0
0
1 n 1 1 1 o 1 P I I I I _j_ J I l_l__ltlll
40 45 50 60 65
TEMPERATURE IN DEGREES FAHRENHEIT
Figure 34. Mortality of sockeye smelts tested at various
te-mperatures during the course of the migration
1959.
•
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~r
' 1
1
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: l
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121
Similar series of tests were conducted in 1960 and 1961 yield-
ing comparable results.
The highest mortalities recorded in this way were 35
per cent. Surviving fish were in an abnormal condition for
some time following testing with numerous fish lying on their
sides for several hours. When disturbed and induced to swim
about, such fish occasionally died also.
Two possibilities exist for the sudden appearance of
embolism mortalities. The excess gas may have originated
through internal supersaturation; this supersaturation resulting
--from fish rising into the warm waters of the lake surface
from depth immediately prior to downstream migration, there-
after being trapped and tested before achieving gaseous equili-
bration with their new environment. The second possibility
was that of gas embolism due to the entry of swimbladder gas
into the blood stream on decompression.
Smelts held at lake surface and depth. The relative
permanence of the lethal factor was examined by holding sam-
ples of smelts varying periods of time between trapping and
testing. Smelts trapped and tested with a few minutes evi-
denced a mortality of 19 per cent. The mortality declined
rapidly when smelts were held in warm lake-outlet water prior
to testing (Fig. 3 5) • Mortality declined to 2 per cent within
3 days of pre-test holding.
122
The gradual loss of the lethal factor described above
raised the possibility that it was due to an environmental
pressure-conditioning that could be replica ted experimentally.
In order to test this, 400 sm9lts were trapped migrating from
Cultus Lake in mid-June. One hundred tested immediately
showed a mortality of 19 per cent. A second sample of 100
held in warm lake-surface water (Fig. 36) for 3 days evidenced
a mortality of 2 per cent. Following 3 days of residence in warm
surface water the remaining 200 fish were held at a depth of
40 ft in the lake for 7 days. A sample of 100 of these fish
was recovered from depth and tested immediately, resulting
in a mortality of 21 per cent. The fourth sample of 100 fish
was held an additional 2 days in warm lake-surface water and
showed an 11 per cent mortality on testing. The lethal fac-
tor thus was lost under conditions of lake-surface residence
and recovered with residence at depth.
Increased content of dissolved gases. The gas content
and hence saturation change, corresponding to that which
smelts would experience migrating from thermocline to surface,
was duplicated in the pressure chamber. Groups of smelts
exposed to air saturation of 100 to 110 per cent at a pres-
sure of 2 atmos (absolute saturation 50 to 55 per cent) showed
a slightly increased mortality on testing following a 24 hr
exposure to such water. Similarly, sample of smelts exposed
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20r-----------------------------------------------------~
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ct:
0
2 10 .... z
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_____________ _ Figure 3 5 •
MID JUNE 1961
\
12 24 48
HOLDING TIME IN. HOURS
Decline in mortality among groups of smelts
held up to 72 hours in Sweltzer Creek before
testing,
•
72
(
\. ''" -:'1'. ·4.
~-
124
MID JUNE 1911
deptlt tei'Ap Na
ft ., ,.,. ..
0-70~15.8-
10
20
30
40
I
A • amolta teated mioratino out of lake
I · aimilar mioranta held 3 doya In turtace water
C • aimilar mloranta held 7 dar• at 35 feet
13 11.2
eo 16.9
52 19.4
49 19.7
47. 19.8
per cent
mortality
19
2
21
D • · depth· held tith re ·held 2 daJt in aurface water II
... _________ _!figure 36. Mortality among smolts accompanying residence in
surface and thermocline waters.
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•
3 . &
Figure 37.
125
•
e
110-120 ~
12 24 48
TIME IN HOURS
Mortality among smelts following. exposure to water
of increased air content. Gas tensions· expressed
as per cent of saturation at atmospheric pressure •
•
126
to air saturation of 110 to 120 per cent evidenced a gradually
increasing mortality on testing with increased duration of
exposure. Finally, markedly increased gas tensions in which
the air saturation was 130 to 140 per cent resulted in sharply
increased mortality on testing following 3 hr of exposure
(F-ig. 37 ).. Maximum mortality appeared after 12 to 24 hr of
holding in such water of increased gas content.
Changes in temperature. The saturation change due
to irlareased temperature accompanying movement upward from
the thermocline to the surface also was duplicated in the pres-
sure chamber. Groups of 100 smolts were acclimated for 2
days to a constant temperature then. subjected to a sudden
increase 5 min before conducting the standardized decompression
test. The mortality remained below 6 per cent for increments
of increase of less than 13°F. For increases of 14 to 19°F
mortalities of 10 to 20 per cent were recorded (Fig. 38) •
The acclimation waters were not always at air satur-
ation and hence tihe:t·incretrrents of increase in temperature were
corrected to per cent saturation at the increased temperature.
No clear trend is apparent (Fig. 39) between mortality on
testing and temperature-induced increase in saturation.
·~ l
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--1 0 I I I I I I I I I I I 1 l l 1 __j_ I I I
0 5 10 15 20
,-1 TEMPERATURE INCREASE IN DEGREES FAHRENHEIT
'--0 ~ 10
] TEMPERATURE INCREASE IN DEGREES CENTIGRADE
Figure 38. Mortality decompression following sudden on
J increase in temperature. Open circles increment. s
I
]· above 45.,F ~ solid circles above 55., F. ~
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0 • ]
0 • 0
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0 I I I I I I I I I I I J _l 1 _t _l_ I I :1
9~ 100 110 120 130
PER CENT SATURATION
Figure 39. TempE·ratur•" increases expressed as increases i:-: I
pf~r Ct=-'nt saturation. .I
•
J
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129
Swimbladder gas and resistance to decompression
Increased and decreased gas content of the bladder.
The smolts held 48 hr at 30 psi above atmospheric pressure
with an air lock above the water surface quickly inflated their
swim bladders to neutral buoyancy. On testing with the
standardized decompression test, these fish showed a mortal-
ity of 25 per cent, compared with zero mortality among neg-
ative-buoyancy fish (below). Unfortunately the air lock
supersaturated the water flowing through the chamber up to
a maximum of 118 per cent, thus complicating the experiment.
The experiment was repeated at a lower pressure ( 15 psi
above atmospheric) and a shorter period of exposure of 90
min as before, the smolts came to neutral buoyancy utilizing
atmospheric air. The decompression test resulted in a mor-
tality of 12 per cent of the fish. Two groups of 50 smolts
were tested under conditions of swimbladders inflated to
atmospheric pressure and these samples had an average mor-
tality of 2 per cent.
The group of smolts exposed to gradually decreasing
pressure below atmospheric conditions lost gas from the swim-
bladder and attained neutral buoyancy at a vacuum of ·25 in
Hg (an absolute pressure 125 mm Hg). On being subjected to
the standardized decompression test no mortality was observed
among the 50 smolts in the sample.
s
l:!g
130
Bladderless and catheterized-bladder fish. A sample
of 20 prickly sculpins subjected to the standardized decompres-
sion test evidenced little ,~:aiscomfort on sudden exposure to
vacuum conditions and no subsequent mortality. Groups of
sculpins exposed to water of 130 per cent of air saturation
at 2 atmos (absolute saturation 65 per cent) for 24 hr and
96 hr also showed no mortality when exposed suddenly to
vacuum conditions.
Ten control sockeye and 10 smelts with catheterized
swimbladders were subjected to the standardized decompression
test following 24 hr of holding at 2 atmos pressure in water
at 130 per cent of air saturation. These test conditions
were identical to those described under the se:ation on changes
in wat'er saturation. Control sockeye showed a· mortality of
5 fish on exposure to vacuum conditions. The catheterized
sockeye lost gas from the swimbladder t:;hrough the catheter
on decompression and evidenced no mortality.
Duct-release pressure and sockeye held at depth.
Yearling sockeye held for 7 days at a depth of 40 ft in the
lake showed an average duct-release pressure of 19. 6 mm Hg
with +13 .2 mm Hg for one standard deviation. Control fish
held at the same temperature and surface pressure had an
average pressure at release of 21:;.;3 mm Hg with .:!:,17. 5 mm Hg
for one standard deviation and were not different from the
r
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~\::,:]
131
fish held at depth. Thus the appearance of swimbladder gas
as emboli appears not to be due to increased constriction of
the pneumatic duct following residence at depth.
Equilibration of fish with dissolved nitrogen of the environment
Rate of change of nitrogen in venous blood. The reduc-
tio:q' in nitrogen in venous blood of fish following transfer from
water of nitrogen content of 17.5 to 13 .-o ml per liter is
shown in Fig. 40. It is clear that dissolved nitrogen in venous
blood very quickly declines to the level of the control fish,
with slightly less than half of the excess nitrogen being lost
during the first 5 min after transfer. Complete equilibration
was attained between 30 and 60 min after transfer from water
of high nitrogen tension.
The attempt to measure nitrogen in arterial blood under
the same experimental conditions was unsuccessful as the ar-
terial sample could not be drawn without interfering with res-
piration. Thus it was not possible to calculate the rate of
clearance of dissolved nitrogen from blood by measurement of
nitrogen in arterial and venous blood and cardiac output.
Rate of equilibration of total dissolved nitrogen.
The dissolved nitrogen given 1up by an individual fish was
determined at 0, 5, 10, ZO and 30 min (Fig. 41). Approx-
imately 30 per cent of the excess--dissolved nitrogen was lost
./
'---
... z ...
c,)
1.90
1.80
1.70
ffi 1.60
CL ., ... a
31.&0
0 >
z
z ~ 1.40
0
E ... -z
1.30
1.20
1.10
1-
~
8
8
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1-
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1-
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I
-------·--·-------·--0
8
0
0
0
8
~
·, I
10
132
0
0 0
8 0
0 ;
0 one ttondard deviation
8 0
0 0 control mean 0
0 0 §
-
I I I I
15 . 20 30 60
TIME IN MINUTES
Figure 40. Dec·rease in nitrogen in venous blood following trans-
fer o.f fish from water of 17.5 ml per liter nitrogen
to 13. 0 ml per liter .
•
-~
l
l
-j
- J
' 1
J
J
]
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z
8
G:
1--z
~
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I
IOOr-~------~------------------~---------------
80 0
0
I
60
8
0
~ . § r~ ·_;.~
j:·
g ------------i i
40 0
0
0
0
0
20
0~~----~----~----~------L-----~----~~
0 10 ·~ 20 2~ 30
TIME IN MINUTES
Figure 41. Per cent of excess nitrogen retained by fish
following transfer from water of 14.4 to 1.6
ml per liter nitrogen.
•
134
in the first 5 min after transfer to water low in nitrogen
and 60 per cent by the end of 3 0 min. These values may be
slightly low as the solubility of nitrogen in the intact fish was
arbitrarily placed at that of water. Thus the test fish may
have given up a slightly larger percentage of their dissolved
nitrogen than the calculationsiini:ii.aaire.. The date -:suggest that
one-half of excess dissolved nitrogen is lost in approximately
20 min and the remaining one-half takes considerably longer,
possibly 1 to 2 hr.
--------------
I
']
1
~~' l
J
·1 ~~~~~r
I 4 ~.:-....
l
J
J
~ J -
J
' l
136
alevins before the swim bladder has been inflated. Alevins
and fry, lacking a gas phase, do not respond to increased
density as is the case with fingerlings. Nor is there evidence
either in the literature or in this study that sockeye have a
true sense of pressure. Thus alevins and fry may be able to
reside in the spawning redd at some depth in the lake» with-
out undue stimulation due to hydrostatic pressure.
Young Salmonidae initially fill their swimbladder~ by
gulping atmospheric air at the water surface (Vogt » 1842).
Th~s is true also of certain physoclists (Ledebur, 1928 ). The
air-gulping instinct in response to negative buoyancy is lost
subsequently in-physoclists but retained throughout life in many
physostomes (Frisch and Stetter, 1932). Swimbladder fill-
ing takes place approximately at the time Atlantic salmon fry
emerge from-the gravel (Hoar, 1937). Chum salmon alevins
reared in hatcheries may gulp air prematurely ( Disler, 1953).
Disler's observation was confirmed by the author (unpublished)
on sockeye alevins which had access to atmospheric air during
hatchery incubation. Alevins inflated their swimbladders mid-
way in development between hatching and emergence.
Fry emerging from the gravel swim upward to the
water surface and swallow air into the swim bladder. The
question arises whether fry develop a sensitivity to pressure
and hence swim upward, or whether the compensatory-
~ l
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~-1
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: 1
: 1
J
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J
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J
J
137
swimming response to pressure follows swim bladder inflation,
the latter being a response to increased density. For fry
emerging in shallow water, pressure stimulation would be very
slight. The evidence for premature filling of the bladder
also tends to argue against pressure being involved. If a
developing pressure sensitivity induced fry to swim upward,
then swimbladder filling should have appeared closer to time
of emergence. For these reasons, the upward swimming of
emergent fry is regarded as compensatory swimming in res-
ponse to negative buoyancy. This activity tends to carry fry
___ 1:o the water surface where instinctive gulping of air and
bladder inflation follows.
The problem of maintaining preferred depth. In con-
trast to fry, sockeye fingerlings and smelts showed a char-
acteristic compensatory swimming in response to pressure
(Fig. 16 and 17). This compensatory swimming provides some
indication as to the pressure preferred by young sockeye and
how the corresponding depth is maintained. It should be
noted that this compensatory swimming is in response to
increased density and not pressure per ~. This was dem-
onstrated by reducing the gas content of the swimbladder
and inducing compensatory swimming at atmospheric pressure.
Also by making air available to sockeye under pressure, the
fish soon reached neutral buoyancy and compensatory swimming
138
ceased in spite of the increased pressure.
As compensatory swimming is a response to negative
buoyancy, the significance of this response is more apparent if
it is expressed in relation to the density of the fish. In Water,
the greatest percentage change in the volume of a gas occurs
close to the surface (Fig. 42) • Correcting this change in gas
volume to change in density of a smolt (Fig. 43) it is obvious
that the most rapid change in density takes place as the fish
descends from or rises to atmospheric conditions. Expressing
the rate of beating of the pectoral fins in relation to smolt
---density (Fig. 44), there was no apparent response for almost
one-third of the potential increase in density. Thereafter
movement of the pectoral fins increased rapidly and reached
maximum frequency coincident with approximately one-half of
.~J
ma..otimum density.
This density increase with depth is altered profoundly
by the soundin_g behavior of the fish (Fig. 45). For this
reason it was essential that sockeye fingerlings and smolts
to be tested be permitted to inflate their swimbladders to
neutral buoyancy at atmospheric pressure.
The compensatory swimming of sockeye smolts in res-
ponse to pressure would suggest these fish prefer the range
from lake surface to a depth of perhaps 40 ft. A number of
observations have been made on the vertical distribution of
~.J
cl
c ... . ~-~
0.125
139
0 2 .3 4 5 6 7 8 9 10
PRESSURE IN ATMOSPHERES
0 34 68 102 136 170 203 237 271 305
DEPTH IN FEET
Figure 42. Change in unit volume of gas in relation to depth
and pressure.
•
~ "'-...
"' a -... 1.05 z
"' ()
. ,, _. _;, . ()
ii . B a.o•
II:
"' -a.
. .,
_ --~---~-IA)3
-II:
0
. ·--z--:-,..
t: 1.02 .,
z
"' Q
1.01
1.00
0
. -----------------
140
-----------------------------------------------J--
2 3
0 34 . 18
4 ' 6 7
.. ·----~ . .. '.
---
8
--
9
PRESSURE IN ATMOSPHERES
102 136 170 203 237 271
DEPTH IN FEET
10
30S
Figure 43. Change in the density of a sockeye a molt with
increasing depth and pressure.
' ~·· ,-,
n
J ' __
.··.:··:· . ~.,.:., ·?:(:~-~-.:·.-'::.
141
190,....--------------------------~
a:
"' 0..
-'-----en --
~
"' CD
z -~
;l
~ u
"' 0.. 160
1&01~~------_. ______ ~~------~------~------~------~~ 1.05 1.06 1.00 1.01 ID2 1.03
DENSITY
1.()4
Figure 4Jt.·. ·Pectoral fln beats ln relation· to sockeye smolt
density. Theoretical line joins first and final
values.
•
-"·"··
142
-------------------------------------------------
r
L
' ' L
.....
2 ·3 4 ~ 6 7 8 9 10
PRESSURE IN ATMOSPHERES
0 34 68 102 136 170· 203 237 271 305
~~,~~
~: __ ._;§)~,
DEPTH IN-_FEET
The effect of sounding on pressure-induced change in Figure 45.
density. Heavy line mean and light lines ranie of
response. Upper broken line maximum density, sv1im-,_
.. -'--., ~,.. .. bladder free of gas, upper light lines twQ standard
deviations.
-~
-~~
~·
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143
of young sockeye in the lake environment and these may be
compared with preferred depth determined experimentally.
Chamberlain ( 1907) caught young sockeye at depths of 15 to
60 ft during daylight and at the lake surface during darkness.
Foerster (1925) noted the absence of young sockeye from the
surface of Cultus Lake in contrast to the surface habits of
this species reported to him for Crawford Lake. Foerster
caged hatchery sockeye at depths of 2 to 30 ft and noted the
fish held at 30 ft obtained more food than those in shallower
water. Ricker ( 1937) found food was sparse in the epilimnion
__ and believed light diminshed in the hypolimnion. He suggested
accordingly feeding was in the layer between 5 to 15 m.
Krogius and Krokhin ( 1948) conducted vertical sampling
in Lake Dalnee. They observed sockeye fry remained in
shallow water for about one month after emergence from the
gravel before moving into deeper water. During the summer
sockeye fingerlings were in the epilimnion with up to 100 per
cent of the fish at the surface. The young sockeye spread
deeper during autumn and by winter were distributed almost
uniformly to a depth of 50 m. Krogip.s and Krokhin believed
the vertical distribution of the young sockeye was related to
the distribution of food organisms •
Johnson ( 1956) described an intense distribution of
young sockeye at the lake surface at first darkness.
144
Johnson ( 1958) noted the disappearance of the fish from the
surface in late October, coinciding with lake overturn and
changes in the .behavior of the fish. Johnson ( 1959) found
young sockeye were distributed at depths of 0 to 5 m during
daylight, corresponding to the depth of maximum abundance of
zooplankton. During darkness the fish spread downward to
depths of 15 m •
Young sockeye salmon are concentrated m the upper
15 ft of Baker Lake durmg the sprmg ( Rees, 1957) but are
distributed as deep as 200 ft durmg fall and W!lter (E.
Quistorff, personal communication). Burgner ( 1962) noted
the movement of fingerlmgs offshore and changes m the ver-r
tical and horizontal distribution of these fish annually.
Gregory and Mathisen ( 1963) found the greatest concentration
of young sockeye at depths of 7 to 13 m with some fish as
deep as 31 m.
Thus the depth preference of young sockeye, as shown
experimentally by Hoar (1954) and in this study, is in keeping
with the vertical distribution found by varicks investigators.
'
Compensatory swimming probably plays an important role in
mamtaining young sockeye at their preferred depth.
The problem of mamtaining buoyancy. The swim bladder
must be regarded as an asset for the maintenance of buoyancy
Delaroche ( 1809). Sockeye appear to have compromised to
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145
some extent the advantages of the swim bladder. Sockeye
smolts showed a bladder. volume of only 5. 96 per cent of the
volume of the fish. This is similar to the volume of 5 .1 per
cent in Salmo trutta (Alexander, 1959c). The small volume
of the swimbladder in sockeye indicates these fish are less
dependent on the swim bladder for buoyancy than are the higher,
bony fishes. The perch, for example, has a bladder volume of
7. 5 per cent (Jones, 1951), 28 per cent greater than that of
the sockeye. This difference is even more marked comparing
sockeye with cyprinids such as the roach having a swimbladder
--volume of 9. 9 per cent (Alexander, 1959b), 66 per cent larger
than that of the sockeye.
The relative dependence of young sockeye on their
swim bladders may be shown by the method Lowndes ( 1937)
described for quantifying the density of an aquatic animal in
relation to that of its environment. His statistic was the
density of the animal divided by that of the environment, times
1000. This Lowndes termed the sinking factor. Young sock-
eye in fresh water with access to atmospheric air showed
virtually neutral buoyancy (Fig. 19). Thus withe swimblfdders
inflated to neutral buoyancy young sockeye would have a sink-
ing factor of 1000. Relative dependence on the swim bladder
is shown by the sinking· factor of such fish free of bladder
gas. At a gas-free density of 1. 0634 g per ml in fresh water
146
young sockeye would have a sinking factor of 1063. Sinking
factors of this magnitude are representative of bladderless
or fish with a.much reduced bladder (Jones and Marshall,
1953) and invariably bottom dwelling. The d.en~S:e".s± of the
pelagic fishes appears to be the mackerel, with a sinking fac-
tor of 1043, for which it may be compensating by rapid swim-
ming (Jones and Marshall) •
There seems little doubt, then, that young sockeye
are dependent, in spite of their low density, on the swim-
bladder for maintenance of buoyancy. Precise neutral buoy-
·-·ancy may not be achieved frequently in fresh water but some
degree of swimbladder inflation is probably adequate to me:e.t
the nee~s of these fish.
This dependence on the swimbladder for buoyancy is
much reduced in the marine environment, due to the greater
density of sea water arid the high fat-content of sockeye.
Taylor ( 1921) calculated a fish (fat-free) of density 1. 076 g
per ml would require a fat content (fat density 0.925 g per
ml) of 29.34 per cent for neutral buoyancy in sea water of
density 1. 026 g per ml. The fat-free density of 1. 076 g per
ml for bony fishes is probably too high for sockeye. Employ-
ing the density obtained for young sockeye, 1. 0634 g per ml
(admittedly not fat-free) a fat content of 24.3 per cent
would bring sockeye to neutral buoyancy in sea water in the
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147
absence of swim bladder gas. Idler and Clemens ( 1959) found
a fat content of 15o 1 per cent in eviscerated~ maturing fe-
male sockeye in sea water o It is apparent that such fish
are much less dependent on bladder gas for buoyancy, with
more than half of their negative buoyancy compensated for
by fat.
For an assumed fat-free density of 1. 0634 g per ml
and fat content of 15 per cent, the density of a maturing
sockeye would be approximately 1 o 042 g per ml o At an
environment density of 1 o 026 g per ml the sinking factor be-
comes 1015o Thus maturing sockeye in the marine environ-
ment have perhaps one-quarter of the sinking tendency of
young sockeye in fresh water o It is suggested such fish are
dependent very little or not at all on the swimbladder for
maintenance of buoyancy.
It is noteworthy that maturing sockeye evidenced the
small and thickened swim bladder Hoar ( 1.937) described in
adult Atlantic salmon.
The problem of restrictions imposed by the swim bladder.
The rapid change in ;volume of a gas with depth, particularly
near the surface, places restrictions on ·the vertical move-
ments of fish possessing a swim bladder. Swimming downward
below their level of neutral buoyancy, fish become progres-
sively more dense and are obliged to add gas to the swimbladder,
148
if buoyancy is to be maintained. Swimming upward, fish be-
come progressively less dense and if the fish was adapted to
some depth~ gas must be removed from the bladder or the
fish may be buoyed helplessly to the surface. Jones (1951
and 1952) has described these restrictions for the physo-
clistous perch.
In sockeye salmon the restrictions of the swimbladder
are minimized in a number of ways o The percentage volume
of the bladder is small and hence there is less gas 9 relative
to the size of the fish, to expando Other factors being
~qual, this small volume of gas would permit sockeye a
greater vertical range than that enjoyed by fish such as
cyprinids, having a relatively large swim bladder.
The upward movement of sockeye is facilitated by the
possession of an extensible swim bladder. In the study of
bladder extensibility, the volume of the bladder increased an
average of 83 per cent beyond the volume at neutral buoy-
ancy, before gas escaped. These results suggest young sock-
I
eye are tolerant of considerable expansion of the swim bladder,
almost doubling the volume without gas loss. Accordingly,
sockeye may be capable of making vertical migrations without
concern for swim bladder expansion. It remains to be demon-
strated that sockeye do in fact ever permit the volume of
the swim bladder to exceed neutral buoyancy.
149
In the physostomous sockeye the restrictions imposed
by the swimbladder are lessened further by the tendency of
this fish to emit gas ( 11 Gasspuck 11 reflex) on reduction in
pressure o Gradual decompression to a vacuum of 25 in Hg
was accompanied by the periodic emission of bladder gas by
the fish, such that a slightly negative buoyancy was main-
tained o It is suggested therefore, that sockeye would exper-
ience little difficulty in releasing excess gas from the swim-
bladder during ascent. This would be necessary only if sock-
eye inflated their swimbladders in excess of,. neutral buoyancy
relative to surface pressure.
Rapid decompression may not permit the escape of
swim bladder gas. Hence the swim bladder damage and mortal-
ities among physostomous sockeye resulting from passage
. J
through turbines •
The restriction of vertical movement by fish is re-
I .J
lated also to the pressure of gas within the swim bladder. In
!
sockeye, pressure within the bladder was found to be equal
j that of the environment. In contrast, Alexander ( 1959a)
~ l found an excess pressure of 108 mm Hg in the swimbladder of
the bream o Alexander regards excess pressure in the cyprinid
bladder as an adaptation for more precise maintenance of
buoyancy over the narrow range of depth to which the fish
is adapted. That is, excess pressure within the bladder
150
reduces the significance of the pressure of the environment.
The maintenance of this excess pressure requires a relatively
tough and inelastic bladder' restricting the vertical range of
the fish. Sockeye possess a thin-walled and extensible swim-
bladder, incapable of maintaining an excess pressure and of
restricting the vertical migrations of the fish.
The restrictiveness of the swimbladder is increased by
the secretion of gas into the bladder. That is, during
ascent, excess gas must be removed from the bladder either
by resorption or emission. Young sockeye showed no ability
-to secrete gas, either when held beneath screens or under
pressure. Thus sockeye fingerlings may be free to migrate
to the surface without being required to emit gas from the
bladder.
The problem of escape from predators. When fright-
ened, the fry of chum and coho salmon seek cover and pink
salmon fry scatter at the surface (Hoar, 1958). In response
to fright, sockeye fingerlings and smelts sound into deeper
water. This fright response is regarded as an adaptation to
1:he lacustrine environment, sockeye thus making use of the
vertical dimension available to them.
The sounding response of sockeye is accompanied by
the partial expulsion of gas from the swim bladder. This
usually approximates one-third of the bladder gas, but may
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151
approach three-quarters. The function of the gas expulsion
while descending (in contrast to herring which expel gas on
ascending, Braun, 1962) remains open to speculation. The
The accompanying increase in density perhaps accelerates the
rate at which sockeye are able to swim downward. The
exact value of gas expulsion perhaps can be determined through
blockade of this adrenergically controlled mechanism with
"dibenzyline" followed by measurements of sounding rates of
treated and control fish.
Young sockeye in Cultus Lake are the object of in-
tense predation (Foerster, 1938; Foerster and Ricker, 1941;
Ricker, 1941). The important predators in the lake are
squawfish, trout and char. These fish are relatively large in
relation to under-yearling sockeye, and as swimming speed is
a function of fish length, should have little difficulty in out-
performing the smaller sockeye. For young sockeye living in
the region of the thermocline, the sounding response would
tend to carry these fish into the poorer light of the hypolim-
nion and perhaps some pJ["ot:ection from predators.
It is noteworthy that th_e sounding response continues
to be present in adult sockeye. When trapped in purse seines,
sockeye attempt to sound under the net and the fishermen
" anticipate their catch by the extent of the bubbles rising to
the surface.
152
A more thorough discussion of the sounding response
may be found in Harvey and Hoar (unpublished manuscript) •
The problem of gas disease in sockeye during vertical
migrations in stratified lakes. There is some evidence that
young sockeye salmon make vertical migrations from cold
thermocline to warm surface waters. Ricker ( 1937) has
suggested y~arling sockeye may be making excursions from
the thermocline into the epilimnion, even to the extent of
taking insects from the surface. Harvey ( 1962) presented
evidence that late-migrating smelts commenced their migration
. from the depth of the thermocline or greater o Such fish
would thus pass upward through markedly warmer water,
then exit from the lake in a flow of warm surface-v-.Tater.
The upward movement of young sockeye in a thermally
stratified lake has several consequences o The fish experience
a rapid incre~se in temperature, a decrease in dissolved gas
in the environment, a rapid decrease in pressure and through
this, an increase in absolute saturation of both fish and
environment. Thus sockeye rising from a depth of 50 ft to
l
surface 'conditions in August of 1961 would experience an
increase in temperature from 48 to 73°F (Fig. 24) ~ an in-
'
crease of 25 Fahrenheit degrees. Based on Brett ( 1952)
a temperature of 73 °F may be slowly lethal to sockeye. The
more immediate consequences would include a sharply increased
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153
saturation of nitrogen internally. From the nitrogen data of
July, 1961, fish arriving at the surface would have an inter-
nal saturation of nitrogen approaching 136 per cent (Fig. 30}.
Absolute saturation would not exceed 100 per cent until the
fish were within approxirm.tely 12 ft of the surface. There-
after absolute saturation would increase rapidly (Fig. 46)
toward 136 per cent. As described previously, the possible
consequence of this decompression, plus saturation increase,
is the "bends". This is obviated through the rapid rate of
nitrogen equilibration between fish and environment (Fig. 40
and 41) • This is not regarded, of course, as a unique adap-
tation of sockeye salmon. Rapid equilibration of dissolved
nitrogen is a process of passive diffusion and thus should be
common to fish in general. It does explain, however, how
pelagic fishes such as sockeye are able to pass upward through
a thermally-stratified body of water without developing gas
disease.
The rapid clearance of dissolved nitrogen described
above does not protect fish from developing gas disease in
supersaturated water. Surface water saturations in excess
of 100 per cent are relatively common in lakes during the
spring period when water_ temperature is rising more quickly
than gas is being lost. Ricker ( 1937) found surface satur-
ations of 104 per cent during spring and Harvey ( 1962)
154
measured oxygen saturations of 110 and nitrogen of 107 per
cent. Saturations as low as these are not usually lethal to
adult fish (Harvey and Smith, 1961) although sockeye alevins
are prone to gas disease at low levels of supersaturation
(Harvey and Cooper, 1962) • Foerster ( 1925) reported
oxygen saturation as high as 127 per cent ( 133 per .cent cal-
culated to the theoretical solubilities, Handbook of Chemistry
and Physics) for Cultus Lake in August, 1923. Such satur-
ations would approach lethal conditions for surface dwelling
fish. These high saturations in the epilimnion occurred the
day following intense mixing by storm action and the oxygen
values presented by Foerster are considerably higher than
would be expected following air-equilibration.
A less common but more serious form of lake-surface
supersaturation is that resulting from photosynthesis.
vvoodbury (1941) measured oxygen saturations on the surface
of Lake vvaubesha (vvisconsin) ranging from 171 to 306 per
cent and attributed to this the deaths of a variety of fishes.
In· .the present study of dissolved gases in Cultus Lake,
oxygen supersaturation through photosynthesis was limited to
the depths of 15 to 50 ft. The absolute saturation remained
below 100 per cent and hence mortalities such as described
by vvoodbury could not occur.
rl
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-I The problem of tolerance to pressure and resistance
to decompression. The utilization of the vertical dimension
: J of the lake environment re_quires young sockeye to have a
rj tolerance to pressures much in ;excess of atmospheric. The
ascent of sockeye from depth requires these fish to tolerate
r 1 decompression.
' J
In the pressure apparatus, young sockeye tole~ated
pressures up to 20 atmos, equivalent to a depth of 680 ft.
J This is considerably greater than-~·the depths which young
J sockeye are known to inhabit: ZOO ft, Quistorff (personal
communication) and 50 m, Krogius and Krokhin (1948).
~J
L._
Neave (1960) reported sockeye were netted as deep as 200
:J
ft during sampling in the eastern Pacific. It is possible
therefore, that pressure does not limit the lower range of
J sockeye salmon. Other factors such as light, food or tern-
: J
perature may determine vertical distribution of sockeye.
Resistance to decompression was variable, depending
on whether or not sockeye were decompressed to pressures
below atmospheric (Fig. 31 and 32). Resistance to decom-
pression varied seasonally (Fig. 34). Mortality of smolts was
associated with residence at some depth in the lake (Fig. 36).
Mortality on decompression was induced experimentally through
increased content of dissolved gases (Fig. 37) and increased
temperature (Fig. 38). In spite of these environmental
156
factors influencing mortality, there is little doubt that the
embolism-induced deaths were due to emboli originating from
swim bladder gas.
As these mortalities appeared only with rapid decem-
pression, it is unlikely that the relatively gradual decompres-
sion accompanying ascent in lakes would result in comparable
mortalities. Furthermore, decompression below atmospheric
pressure is equivalent, in so far as expansion of swim bladder
gas is concerned, to the ascent from depth of sockey having
their swimbladders inflated to provide buoyancy at depth.
Thus the exposure of aoc:l{eey:e (swim bladders inflated to neu-
1 tral buoyancy at atmospheric pressure) to a pressure of z
atmos ( 15 in Hg vacuum), is equivalent to sockeye migrating
to the surface from a depth of 34 ft (swim bladders inflated
to neutral b~oyancy at that depth, a pressure of 2 atmos).
Until it has been demonstrated that sockeye do inflate their
swimbladders at depth, this problem may be assumed not to
arise naturally in the lake habitat. Decompression of fish
to pressures below atmospheric does occur during passage
through turbines.
The problem of the temperature barrier to the do,wn-
st;ream migration of sockeye smelts. Chamberlain ( 1907)
in his study of young salmon in the Naha River (Southeastern
Alaska) observed sockeye yearlings comm,enced migrating in
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157
large numbers at about 45°F ( 1903) and the migration ended
at 50°F (1904).
Ward ( 1927) noted young sockeye remain in the reser-
voir, Llake Shannon, behind the then newly constructed Baker
Dam. After the lake surface warmed, Ward believed these
fish retired below the thermocline and spent the summer in
deeper water. He did not know whether these sockeye con-
tinued their migration in the fall or became landlocked. Ward
(1932) expanded on this idea. He observed ~olts entered
the reservoir during filling and hence at a time when water
---was not necessarily being spilled from the surface. Con-
currently the surface waters warmed and when temperatures
rose above 50°F the migrants were no longer seen and
appeared to Ward to have deserted the surface for deeper
layers. In doing so the smelts were barred from leaving the
lake and were described by Ward as being physiologically land-
locked.
Foerster ( 1937) termed this cessation of smelt mi-
gration by epilimnial temperatures a "temperature barrier or
blanket". Foerster suggested the cessation of migration of
sockeye smelts from Cultus Lake was related to the for-
mation of such a temperature blanket in the epilimnion.
Foerster's evidence for this included the relative frequency
of smelts remaining on iri the lake for a second year and
158
then migrating as two-year-old fish. The yearling migration
of 1934, the end of which coincided with exceptionally high
temperatures, was :followed in 1935 by an exceptionally large
fraction of two-year-old smelts o Precise temperatures could
not be given for the thermal barrier; the migration was 80
per cent complete at 51 °F and terminated at an average of
Parker and Vincent ( 1956) described the migration of
sockeye smelts out of Kitoi Lake (southeastern Alaska) o
The major portion of the smelt migration passed the outlet
~-at temperatures ranging between 44 and 50 °F. The migration
ceasad·:Wh.En surface waters reached 55°F or above ·:and. warm
water extended to a depth of 16 ft. Parker and Vincent
advanced the hypothesis sockeye avoid temperatures below 40 °
F and above 55°F. A small migration of stragglers continued
at temperatures of 55 to 60°F.
Burgner ( 1962) reported the relationship of temper-
ature to smelt migration from Lake Nerka, Alaska. For
five of the six years of study, 90 per cent of the smelt
migration coincided closely with water -t;emperature reaching
50 °F. Burgner concluded the cessation of migration was
associated probably with a change in epilimnion temperatures.
Burgner noted however the greatest concentrations of sock-
eye fingerlings on Lake Nerka were observed after lake surface
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159
temperatures exceeded 50°F, the largest single surface catch
being made at 61 °F.
Lest the above discussion tends to convey the impres-
sion that sockeye migrations only terminate through high sur-
face-temperatures, it might be useful to offer an example
where a migration stops at a relatively low temperature.
At Chilco Lake, B • C. (elevation 3, 845 ft) sockeye smolt
migrations commence at about 38 °F and cessation coincides
with a temperature of approximately 45°F. Nevertheless
some yearling sockeye stay on in the lake for a second year.
One might postulate that had he studied the migration from
Chilco Lake rather than Lake Shannon, Ward might have con-
eluded young sockeye avoid temperatures in excess of 45°F,
rather than 55°F.
Roos (personal communication) observed sockeye smolt
migrations out of Chignik Lake, Alaska, commenced at temper-
atures of approximately 38°F, were 95 per cent complete at
46°F and almost complete at temperatures of 50 °F or less.
In the present study, the results of the decompres-
sion tests on migrating smolts bore directly on the concept
of a thermal barrier to migration. Also pertinent is the
smolt migration and temperature data collected concurrently
at the outlet of Cultus Lake. The smolt migration, plotted
chronologically in Fig. 2, differed considerably in relation to
-1
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160 I
"'
temperature o The 1960 migration commenced at approximately
46oF, was 56 per cent completer.ait 50°F and 99.7 per cent
complete at 55°F o Thus for the 1960 migration it appears
rather that the migration was very nearly complete before
the barrier commenced to exist o In 1961 the migration was
considerably the more prolonged. It was 94 per cent com-
plete at 55°F, 95 per cent at 60°F and 98.7 per cent at
65°F. In effect the migration proceeded without interruption
during the period of warming of the lake surface o
Decompression studies indicated the late migrating
--smolts were not originating from surface water but rather
from some depth, perhaps the region of the thermocline.
The sudden increase in mortality of smolts on decompression
coincided with lake-surface water warming to 51 °F (Fig. 34). . ,
This may indicate that 51-°F is the minimum temperature tend-
ing to depress sockeye from surface water. The relatively
rapid decline in mortality with holding in surface water places
·'
a time limit on the period of surface residence be:Eo~e the
1. I
fish pass through the lake outlet and hence are trapped and
tested. These results suggest smolts are leaving the depth
of the thermocline (or greater) and very soon thereafter
entering the outlet stream, Sweitzer Creek. The results
indicate also the thermal barrier is by no means an absolute
barrier to sockeye in condition to migrate. On the contrary,
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the barrier appears to be relatively permeable, as shown by
the migration of more than 9, 000 fish June 1, 1961. On
that date lake temperatures increased uniformly from 48°F
at a depth of 30 ft to 65°F at a depth of 1 ft below the
lake surface.
CHAPTER V
SUMMARY AND CONCLUSIONS
Summary
1 o Pressure did not influence the behavior of sock-
eye fry prior to initial filling of the swimbladder.
2. Sockeye fingerlings and smolts evidenced compen-
sa tory swimming in response to pressure. Compensatory
swimming was invoked at a density approximately one-third
of the maximum for the fish.
3. Yearling and two-year-old sockeye made less use r
of the pectoral fins and compensated for increased·--.. density
by more rapid swimming.
4. The volume of the sockeye swim bladder was 5. 9
per cent of the volume of the fish.
5. The excess pressure within the sockeye swim bladder
was 0.2 mm Hg. The pressure within the bladder did not
differ significantly fro~ -':that of the external environment.
6. The swim bladder of young sockeye proved very
extensible. Among smolts killed by an overdose of anesthetic,
bladder volume increased an average of 83 per cent before
gas escaped through the pneumatic duct.
163
7. Isolated loops of swim bladder, taken from yearling
sockeye, contracted in response to adrenergic drugs. This
response was blocked irreversibly by the adrenergic blocking
agent 11 dibenzyline".
8. Young sockeye held beneath screens and under pres-
sure failed to increase the gas content of the swim bladder.
There was thus no evidence that sockeye were capable of
secreting gas into the swim bladder.
] 9. When frightened, sockeye smelts sounded and lost
J gas from the swimbladder. Gas loss on sounding was enhanced
by prior exposure to sympathomimetics and prevented by prior
treatment with adrenergic blocking agents.
10. Young sockeye maintained buoyancy by gulping atmos-
pheric air. Inflation of the swimbladder was retarded among
fish treated with the cholinergic blocking agent, atropine.
: _]
11. Among smelts anesthetized to death, an average
pressure of 28 mm Hg was necessary to force bladder gas out
through the pneumatic duct. Atropine treatment reduced duct-
release pressure to 0.2 mm Hg.
12. Histologically, the pneumatic duct of sockeye was
J found to be a convoluted connection between oesophagus and
the anterior end of the swim bladder.
-Lr_' ---c--'"
J
"l
13. A limnological study of Cultus Lake was conducted
in relation to the downstream migration of sockeye smelts. ~l
-I
The temperatures and dissolved gases of the lake were
measured during the year 1961.
" I
14. Young sockeye salmon tolerated pressure up to --1
the maximum tested, 300 psi, equal to pressure at a depth
of 680 ft.
15. Sockeye smelts tolerated decompression from high
pressures to atmospheric conditions. Resistance to decem-
pression below atmospheric pressure was variable. Mortality
of fish was due to emboli originating from swim bladder gas.
16. Smelts migrating out of Cultus Lake after the
lake had stratified thermally were particularly prone to
embolisms on decompression.
17. Mortalities due to embolisms were induced by rapid
decompression of sockeye previously held at the depth of the
thermocline in Cultus Lake.
18. Embolism mortality on decompression was increased
by pre-test increase in the gas content of the swimbladder
and decreased by reducing the gas content of the bladder
before testing.
19. Bladderless fish and sockeye with a catheterized
swimbladder did not succumb to embolisms on decompression.
J
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165
20. No change was observed m the patency of the
pneumatic duct such as to explain the variability of embolism-
mduced mortalities on decompression.
21. Rambow trout evidenced a rapid reduction in
dissolved nitrogen in venous blood following transfer from
water of 17.5 to 13.2 ml per liter of nitrogen.
22. Sockeye yearlmgs transferred from a water of
high to one of low dissolved-nitrogen content, showed a
rapid equilibration with the nitrogen of their environment,
approximately 60 per cent of excess nitrogen being lost m
30 min.
Conclusions
Pressure in the aquatic environment presents fish
with certain physiological problems. Sockeye salmon meet
these problems by adaptation, compromise and fortuity.
Prior to initial filling of the swim bladder, sockeye alevins and
fry are not mduced to swim upward. Following inflation of
the swim bladder, sockeye fingerlmgs respond to increased
density due to pressure by compensatory swimming. Com-
pensatory swimming probably plays a part m the vertical dis-
tribution of young sockeye. In fresh water, young sockeye
have a reduced but nevertheless definite dependence on the
swim bladder for the mamtenance of buoyancy. In salt water,
7
166
the swimbladder is probably of little importance in maintaining
buoyancy. In sockeye, the restrictions imposed by the swim-
bladder are minimized by the small percentage volume of the
bladder, the marked extensibility, the 11 Gasspuck" reflex,
the absence of an appreciable excess pressure in the bladder
and the inability of sockeye to secrete gas into the bladder.
Sockeye utilize the vertical dimension of the lacustrine envir-
onment for escape, sounding into deeper water when frightened.
Sounding is accompanied by the expulsion of gas from the
swim bladder. This is due to the contraction of the circular·
muscles of the bladder under control of the adrenergic com-
ponent of the autonomic nervous system. Young sockeye are
able to make vertical migrations in stratified lakes. The
possibility of gas disease is obviated by the rapid equilibration
of dissolved nitrogen between fish and environment. Sockeye
have a tolerance to pressure and under certain conditions, to
decompression.
In general, sockeye appear well suited to residence and
migration over a range of pressures in the lacustrine environ-
ment. Such fish may be described eurypressural, in contrast
to stenopressural fish having a narrow range of vertical
distribution and movement.
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CHAPTER VI
REVIEW OF RELATED LITERATURE
There exists now an extensive and scattered liter-
ature pertinent to a discussion of fish in relation to pressure.
The swimbladder of fish has been· ·the subject of most such
research. Swimbladder reviews by Jones and Marshall (1953)
and Qutob ( 1962) include discussions of some aspects of
pressure. Other aspects, notably the response of fish to
barometric pressure warranted critical examination. The
effects of compression and decompression on fish similarly
had not been reviewed to date.
Pressure Perception and Response in Fish
Pressure and gas secretion
The original observation that pressure induced secre-
tion of gas appears to be that of Biot ( 1807), who found
that the fraction of oxygen in the swimbladder increases in
direct proportion to the depth at which the fish is found.
Moreau ( 1876) measured gas secretion and resorption in res-
ponse to pressure increase and decrease. Moreau demonstra-
ted gas secretion following partial removal of bladder gas by
puncture, thus establishing fish were secreting gas as a
function of density and not due to pressure per ~. Moreau
Gil rig
168
found also secretion of oxygen increased following sympathetic
section; vagal section produced no change. Bohr ( 1894) ex-
panded the ·innervation studies of Moreau. Bilateral section
of the intestinal branch of the :v;agus supplying the swimbladder
resulted in a decreased oxygen fraction in the bladder and when
the swim bladder was emptied it remained emptied, thus sec-
retion of gas had ceased. From his own experiments and
those of Moreau, Bohr concluded bladder filling was, ·.controlled
by the vagus and emptying by the sympathetic nerves.
That gas secretion was due to a perception of altered
density, as opposed to a perception of change in pressure, is
indicated by the experiments of Woodland ( 1912). Gas sec-
retion was induced. in artificially weighted fish. Conversely,
physoclistous fish artificially buoyed b;Y; attached corks
(Kuiper, 1915) decreased the tension of gas in the bladder.
In the case of a "corked" carp, the fish continued to fill its
swim bladder in excess of neutral buoyancy, leading Kuiper to
conclude the reaction is independent of the density of the
fish. He suggested the inflation of the bladder is probably
controlled by the degree of bladder tension.
Hall ( 1924) confirmed experimentally the changes in
oxygen content with pressure observed by Biot and Moreau.
Perch held at atmospheric pressure showed a swimbladder
oxygen content of 12.1 per cent whereas those maintained
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·~.,..),i" under a hydrostatic pressure of 60 ft for 10 hr had 18.5 per
1 cent of oxygen in the bladder.
I Pressure-induced secretion of gas in the certain physos-
tomes was shown by Evans and Damant ( 1928). The cyprin-
1 oids carp, roach and goldfish, lacking the "gas glands 11 or
c 1
"red bodies 11 of physoclists, achieved neutral buoyancy in 6 hr
under a pressure of 5 ft of hydrostatic head. Roach clearly
l were secreting oxygen which rose from 8. 9 to 25.7 per cent
J of bladder gas.
Gas secretion in physoclists was investigated by Jacobs
1 (1930) who observed that immobilized perch failed to refill
J previously emptied swimbladders. Jacobs ( 1934) confirmed the
observation of Evans and Damant that certain physostomes
'1 '"' were capable of secreting gas into the swim bladder. The
] cyprinids tested and Esox were capable of secreting gas but
salmonids Hucho and Salmo were not.
1 Frisch ( 1934) removed the utriculus from blinded and
control minnows and concluded the labyrinth played no part in
gas secretion. This would r.tiJe O>:ut swimbladder pressure con-
trolling secretion of gas via the Weberian apparatus.
. J
Brown ( 1939) demonstrated the physoclistous guppy
was capable of increasing the gas content of the swimbladder
in response to pressure increase. Small pressure reductions
resulted in gas resorption, but a decrease to 625 mm Hg
170
absolute pressure or less resulted in an increase in bladder gas.
Brown at"t;ributed this to reduced pressure in the bladder
favoring the passage of dissolved gases into the bladder.
Rostorfer (1942) exposed the rock-bass to pressures ranging
from 540 t:o Z,ZZ3 mm Hg, the fish reaching equilibrium at
each pressure. This was achieved through rapid secretion of
oxygen and carbon dioxide, the latter gas then gradually dif-
fusing from the bladder and being replaced by oxygen.
Meesters and Nagel ( 1934) induced gas secretion and
resorption in the perch through increase and decrease in pres-
sure. These processes went on only so long as the fish was
actively moving its fins, suggesting swimming activity-was
reflexly controlling inflation of the bladder. Changes in
resorption were rapid due to quick opening of the oval and the
carbon dioxide constituent of the gas.
Franz ( 1937) investigated the nervous control of gas
secretion and confirmed vagal section reduced the production
of gas. Pressure stimuli within the bladder were conducted
to the central nervous system by the vagus and sympathetic
(splanchnic) nerves. Franz concluded secretion of gas was
regulated by the spanchnic nerve. Spinal cord section, extir-
pation of the cerebrum or diencephalon did not influence for-
mation of gas but Franz located a center of gas secretion in
the mid-brain.
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171
Ledebur ( 1937) in his review of gas secretion and
resorption repeated the observation of Meesters and Nagel
that these processes may be related reflexly to the character-
istic movement of the fins, which Jacobs had shown were
released through the rising or sinking of the fish. Ledebur
concluded gas secretion or resorption should occur only if
these movements could be carried out.
Experiments testing this reflex control of swimbladder
filling were conducted by Copeland ( 1952). Fundulus were
maintained in very shallow water, such that they protruded
above the surface and a control group allowed to swim freely
in an aquarium. Deprived of swim bladder gas, the control
group recovered b}loyancy whereas the shallow-water fish did
not. In a second experiment, fish forced continuously to
swim upward increased the volume of gas in the bladder and
conversely those forced to swim downward decreased it
relative to control fish. On this basis, Copeland advanced
the hypothesis that the reflex receptors controlling the volume
of bladder gas are lo.cated in the musculature of the pectoral
fins, these being the structures used in achieving a new
orientation in the vertical plane.
The hypothesis of Copeland was promptly upset by
Fange ( 1953) who denervated the pectoral fins in the cod by
sectioning the brachial plexus bilaterally. Gas removed from
-1
172
the swim bladder of such fish by puncture was soon replaced,
with test and control fish returning to neutral b'J;.:toyancy within
24 hr and evidencing an increased bladder oxygen content.
Fange concluded movement of the pectoral fins is not neces-
,_ ]
sary for the inflatory reflex. It is unfortunate that Cope-
land's hypothesis was not accompanied by observations on the
response of the pectoral fins. It was essential that he dem-
-l
onstrate a difference in the rate or nature of fin movements
between fish forced to swim upward and downward. Jones I
i
{ 1952) showed the pectoral fins in perch accelerated both in -I
_response to buoying and sinking, although the direction of the
power stroke was reversed. In the present study, sockeye
evidenced increased movement of the pectoral fins both in
swimming upward in response to sinking under increased pres-
sure, and while swimming downward on pressure reduction,
before or during gas emission. In both cases the fish were
angled steeply from the horizontal and the power stroke:
appeared to be in the same direction. It is difficult to imagine
how increased use of the pectorals could lead to gas secretion
in some instances and resorption in others.
Jacobs {1934) was unable to demonstrate gas secretion
in either the brook or rainbow trout. Deprived of swim bladder
gas and denied access to atmospheric air these fish failed to
replace lost gas. This is not surprising, the glandular tissue
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173
being poorly developed and retia mirabilia absent (Jones and
Marshall, 1953). Jacobs' conclusions were in general accep-
tance until the experiments of Wittenberg ( 1958). The lat-
ter worker similarly emptied the swimbladders of rainbow and
brown trout and maintained these fish away from atmospheric
air. Both species achieved up to 50 per cent refilling in 8
days and up to 100 per cent in 13 days. Tait ( 1959) testing
a number of salmonids was unable to verify these results.
Lake char, for example, maintained under pressure showed a
net loss of swim bladder gas, despite observations that among
trout brought up from depth swimbladders were inflated
appreciably in excess of atmospheric pressure.
In the present study, sockeye smelts frightened into
expelling swim bladder gas then held under screens, showed no
tendency to inflate their swim bladders (Fig. 19). Indeed such
fish apparently continued to lose gas from the swimbladder
during the 8 days of study. Similarly smelts held under pres-
sure for 24 hr showed a slight increase in specific gravity at
the end of this time. There was thus no evidence that
young sockeye salmon were capable of secreting gas into their
swim bladders, either in response to an increase in density or
to an increase in pressure.
174
Decompression and gas resorption
Moreau (1876) observed Serranus brought to the sur-
face from 25 m had a much distended bladder. The distention
diminished slowly over several hours. Investigating this
experimentally, Moreau held Labrus at a:. depth of 7 m for
several days. Returned to surface pressure the fish floated
but restored its initial volume after 3 days. Bohr ( 1894)
confirmed these observations on cod. Brought up from a
depth of 14 m the fish were buoyed to the extent of being
inverted at the surface. Within a day the size of the fish
P,ad diminished and oxygen had declined from 52 to 13 per cent
of bladder gas. Bohr did not experiment himself with the
control of swimbladder emptying but concluded from Moreau's
studies that the sympathetic nervous system controlled gas
resorption. Baglioni ( 1908) showed ress;}rption of ga~ was due
to positive buoyancy. Attaching floats to Balistes the fish
were buoyed to the surface.. On removal of the floats a day
later the fish sank to the bottom of the tank and evidenced
a reduction in girth.
The site of gas resorption, Jaeger ( 1903 ) suggested,
was the oval. Reis and Nusbaum ( 1906) described the open-
ing and closing of the oval in Ophidium. Woodland ( 1913) showed
the oval_ of the pollack was closed tightly during active
secretion of gas induced by weighting. Ledebur ( 1929) proved
175
experimentally the oval was the site of gas resorption by
means of a ligature around the bladder, isolating oval from red
gland. Examined later the chamber with the oval was free of
gas.
J Following these early studies on the stimulus and site
of gas resorption, subsequent investigations have been directed
at rate and nervous control of resorption. Jacobs (1932)
measured volume fluctuations in the perch due to swimbladder
J gas. He concluded secretion and resorption of gas were both
rapid and precise enough to maintain the density of the fish
constant during variations in barometric pressure. Meesters
and Nagel (1934) repeated Jacobs' studies on the perch. A
pressure reduction of 5 em Hg resulted in a corresponding
] reduction in volume which was achieved in 10 min. The
J authors attributed rapid gas resorption to quick opening of
the oval. Meesters and Nagel described gas loss from the
:J bladder as diffusion through the oval but were uncertain
whether this was an active or passive process. The rapidly
absorbed component of swimbladder gas proved to be carbon
dioxide, in the absence of which resorption was relatively
slow.
Brown ( 1939) subjected guppies to decreased pres-
sures. At a reduction of 100 mm Hg from atmospheric
pressure, gas was resorbed from the swim bladder restoring
176
neutral buoyancy within Z hr. Larger pressure reductions
favored entry of gas into the swimbladder and the resulting
positive buoyancy became progessively greater. Jones {1952)
measured the rate of gas resorption in the perch and calcu-
lated decompression rates for these fish. A ZO per cent
reduction in pressure required 1 hr and 50 hr were necessary
for a 90 per cent decrease in pressure. From this Jones
showed diurnal migrations with ascents of 5 to 7 hr could
bring perch to the surface from depths not greater than 6
to 7 m.
Fange { 1953) investigated the nervous control of gas
resorption from the swim bladder. The movable muscosa of
the oval formed a mechanism regulating the permeability of
the bladder wall to gases. This resorbent mucosa contracted
with acetylcholine and relaxed with atropine and adrenaline.
Fange introduced carbon dioxide into the swimbladder of
Ctenolabrus and observed its disappearance in 5 to 10 min,
thus demonstrating the high permeability of the resorbent
mucosa.
Brief reviews of swimbladder gas resorption have
appeared in i?la ttner { 1941) , Jones and Marshall { 1953) and
Jones {1957).
Sockeye salmon smolts induced to sound and expel
swimbladder gas, then held under screens, failed to secrete
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177
gas and return to neutral buoyancy. Indeed the density of
·,
the fish continued to increase due either to gas resorption
or to further gas loss through the pneumatic duct. Sockeye
smelts denied access to surface air and held in water of low
oxygen tension {2 ppm) showed a rapid reduction in swim-
bladder oxygen content. Thus gaseous exchange across the
wall of the swimbladder cannot be ignored in these fish.
However the tendency of the fish in the samples to become
more alike in density with prolonged holding under screens
argues in favor of gas loss through the pneumatic duct.
Thus repeated sounding during the period of holding would
.; tend to bring the group to a common maximum of gas expul-
sion. The question of resorption of gas being involved could
be answered perhaps by prolonged holding of fish without
access to atmospheric air. If the density of the sockeye
eventually exceeded that possible through gas expulsion, then
gas resorption across the wall of the bladder would appear
to be involved.
Pres·sure and air gulping in physostomes
Baer { 1835) apparently first observed young fish
gulping atmospheric air at the surface and inflating their
swim bladders. Mortalities among those which failed to do so
r··~.·.·~.· \;_·--·~
178
led Baer to conclude this phenomenon was involved in respir-
ation. Jaeger ( 1904) decompressed tench thus partially
emptying their swimbladders and observed swallowed air
enter~d the bladder and under certain conditions the gut.
Thilo ( 1906) emphasized the importance of air gulping
and concluded this was the main function of' the pneumatic
duct. Thilo also evacuated the bladder of tench by decom-
pression. Allowing these fish access to air. at atmospheric
pressure, swim bladders were re-filled in 3 to 8 hr. Thilo
concluded this was too rapid to be due to secretion and air
entry was by way of the pneumatic duct. Woodland ( 1911)
noted the ease with which physostomes were able to renew
their swimbladder gas by rising to the surface of the water
and passing air through the pneumatic duct.
Evans and Damant ( 1928) studied air gulping in carp,
roach and goldfish. Goldfish which were partly deflated
through decompression, on return to atmospheric pressure
began gulping air at the surface within 5 min and returned to
neutral buoyancy within 1 1/Z hours. Goldfish placed under
an additional pressure of 8 ft of water in the presence of
an air-lock, inflated to neutral buoyancy within 5 min. No
gas was observed in the stomach or intestine. Evans and
Damant examined histologically the pneumatic duct and termed
the fleshy enlargement described by Guyenot ( 1909) , the
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179
pneumatic bulb. Guyenot was of the opinion the duct was
suited only to the exit of gas from the bladder. Evans and
Damant demonstrated gas entry was possible and suggested the
pneumatic bulb served to pump swallowed air into the bladder.
Jacobs (1934) studied air gulping in brook and rainbow
trout, several cyprinids and the pike. Swim bladders emptied
by puncture were re-filled by gulping within 2 to 3 hr in the
case of rainbow trout and brook trout required 6 to 12 hr.
,Rainbow trout . similarly deflated by puncture and occluded from
the surface by screens continued to show negative buoyancy
.. after 27 days. Franz ( 1937) observed air gulping in the min-
now increased with pressure and with weighting of the fish
and concluded the response was due to increased specific
gravity. Moehres ( 1940) reported air gulping was less marked
in the bottom-dwelling cyprinid, the gudgeon.
Plattner ( 1941) decompressed tench, inducing them to
emit gas from the swim bladder. On return to atmospheric
pressure such fish gulped air at the surface. Bilateral sec-
tion of the vagus in Leuciscus stopped secretion and also
paralysed the function of the pneumatic duct. The duct re-
mained closed, the bladder empty and air swallowed by the fish
passed into the intestine. The same result was obtained by
ligaturing the pneumatic duct.
Sockeye salmon readily evidenced air gulping. in the
180
present study. This occurred, for example, shortly after
fright-induced expulsion of gas. The fish returned to the
surface and commenced to gulp atmospheric air within 5 min
of having sounded. Sockeye smelts exposed to pressures in
excess of atmospheric in the presence of an air lock, com-
menced to gulp air almost immediately pressure was increased.
At a pressure of 3 atmos absolute, sockeye smelts increased
the volume of swim bladder gas almost three-fold.
The mechanics of air entry into the sockeye swimbladder
may not be quite the same as Evans and Damant (1928) have
suggested for cyprinids. These authors described a thick-
walled oesoph~gus within which was located the inflating mech-'
anism, the pneumatic bulb. Such a muscular bulb may be nee-
essary to inflate the roach bladder to the measured pressure
of 62 mm Hg. In sockeye, the duct penetrates the wall of
the oesophagus and passes through a bulbous thickening before
becoming continuous with the anterior end of the bladder.
The bulb is much less muscular and this may be in keeping
with the very slight excess pressure measured within the sock-
eye bladder ( 0.2 mm Hg). From observations on the behavior
of young sockeye it would appear air is passed into the swim-
bladder with considerable ease. In the case of the catheter-
ized fish (Fig. 13) air gulped at the surface issued from the
bladder with a few seconds.
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Decompression and gas emission in physostomes
Moreau ( 1876) noted the emission of gas bubbles by the
tench accompanying a reduction in pressure of 4 to 6 em Hg
below atmospheric. Guyenot ( 1909) explored the control of
this loss of gas. He concluded the pneumatic duct functioned
to release excess gas to the exterior. Loss of gas was reg-
ulated in cyprinids by a sphincter which Guyenot termed the
pneumatic sphincter. · The sphincter being closed was inhibited
reflexly by impulses originating through an increase in bladder
volume and conducted to the labyrinth along the Weberian
. ossicles. Guyenot showed a greater reduction in pressure
was necessary to evoke gas emission following interruption of
the Weberian apparatus.
Guyenot's gas-releasing-reflex explanation of the func-
tion of the Weberian ossicles was soon tested and his exper-
iments have been repeated many tirr.es since. Kuiper ( 1916)
took exception to Guyenot's technique and was able to repro-
duce the latter's results only if the fish was in poor condition
and suffering from post-operative shock. Kuiper concluded
neither interruption of the Weberian ossicles nor removal of
the labyrinth, both essential to Guyenot's reflex, influenced
the reduction in pressure necessary to bring about the emission
of gas. Kuiper experimented with vagal section and concluded
from his results that sphincter tone is maintained by the
182
sympathicus and inhibited by the vagus. It is interesting that
Kuiper observed that his fish emitted a few bubbles when
confined and hence frightened but apparently he failed to
recognize the conflict between this observation and the in-
nervation he was proposing.
Kokas ( 1932) , acknowledging the work neither of
Guyenot nor Kuiper, repeated their experiments on the inter-
ruption of the Weberian apparatus with the removal bilater-
ally of the mallei. Before the operation a reduction in pres-
sure of 30 mm Hg evoked gas emission, after the operation
a reduction of 120 mm Hg was required, the latter pressure
forcing open the pneumatic duct. Kokas concluded from these
results the Weberian apparatus formed the afferent part of
the mechanism regulating pressure.
Jacobs ( 1934) acknowledged it has long been known
the pneumatic duct permits gas to escape on reduction in
pressure. He quotes Jaeger's (1903, 1904) view that the
pneumatic duct is to the: .physostome. what the oval is to the
physoclist, namely a mechanism for removing gas from the
swim bladder.
Franz ( 1937) repeated the studies of Guyenot and
Kokas, but could find no hydrostatic function for the Weber-
ian apparatus and concluded the ossicles were not involved in
the "Gasspuck" reflex. In the case of the. minnow, the site
183
or perception of pressure was the wall of the swimbladder
and gas expulsion was due to contraction of the musculature
_l
of the bladder. In addition, both the utriculus and eyes
were involved in gas emission through perception of buoyancy.
Franz found, as had Kuiper, that vagal section resulted in
the disappearance of pesistance to the loss of gas from the
bladder.
Moehres ( 1941) investigated the pressure sensitivity
of the gudgeon as evidenced by gas emission with a reduction
in pressure. Moehres found removal of the pars superior of
_the labyrinth resulted in a temporary increase in the thresh-
hold of pressure necessary for gas release. Extirpation of
of pars inferior, however, resulted in a greater reduction
in pressure being required to evoke spitting; from 13 em of
] water on non-operated fish to more than 40 em post-oper-
atively. Moehres concluded the Weberian apparatus serves a
hydrostatic function in the gudgeon. His results agreed
with Guyenot and Kokas, and Moehres felt the objections to
their techniques expressed by Franz were not applicable here,
since the Weberian apparatus was inactivated quite differ-
J ently. Moehres limited his conclusions to the function of the
Weberian apparatus in the bottom-dwelling gudgeon and sug-
L-\
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gested his results need not necessarily be true of surface-
J dwelling fish.
J
184
Plattner ( 1941) reviewed the conditions evoking gas
emission in physostomes. These included a reduction in external
pressure, an increase in internal pressure, artificial lightening
of the fish and psychic excitation. He confirmed sphincter
opening was inhibited by vagal section or the application of
anesthetics. Plattner agreed gas loss through the pneumatic
duct was an active reflex but did not commit himself to the
nature of the pathway.
Dijkgraaf ( 1941) trained minnows to respond to changes
in hydrostatic pressure of 0. 5 to 1 em of water. Following
interruption of the Weberian apparatus through removal of
both mallei, this response decreased to the extent that an
excess pressure of 40 em elicited no response. Unilateral
extirpation of the malleus did not impair the response.
Dijkgraaf concluded accordingly the Weberian apparatus served
not only in an acoustical capacity, as shown by ·· F.ris,ch
and Stetter, but also in a hydrostatic capacity. Dijkgraaf
( 1942) , using blinded minnows, measured the decrease in pres-
sure necessary to induce gas emission in both intact and fish
in which the incus was removed bilaterally. The result was
a slight increase in the threshhold of gas emission. Dijkgraaf
concluded expansion of the swim bladder can cause emission of
gas without the participation of the Weberian apparatus.
The threshhold of gas emission was raised about 30 per cent
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185
on removal of the incus and thus the Weberian ossicles were
concerned only to a limited extent in the release of the gas-
spitting reflex. Dijkgraaf ( 1950) investigated the role of
direct perception of expansion of the swimbladder by sensory
nerve-endings in the release of the spitting reflex. The exter-
oceptive stimuli and change in buoyancy were eliminated through
removal of the pars superior and permitting the animals to
orient to a horizontal light, changes in buoyancy thus appear-
ing as current. In such fish the reduction in pressure neces-
sary to induce gas emission was almost the same before and
after interruption of the Weberian apparatus. Dijkgraaf con-
eluded the Weberian apparatus perceives the finer variations
in pressure whereas the bladder wall is responsible for the
coarser variations, perhaps above 30 mm Hg.
Fange ( 1953) observed acetylcholine increased the
pressure necessary to open the sphincter of the pneumatic
duct. He suggested the pneumatic-sphincter mechanism is
to some extent homologous to the smooth muscles of the
resorbent area of the euphysoclist. Fange pointed out the
similarities between the deflatory reflex in euphysoclists and
the 11 Gasspuck 11 reflex in physostomes •
In the present study, investigation of the responses
of sockeye smolts to pressure was complicated frequently
by the fright response of the fish. In this the fish dived
186
or sounded and emitted gas from the swim bladder. Harvey
and Hoar (unpublished) have termed this the sounding response
and as a fright reaction have divorced it from the 11 Gass-
puck" reflex. This latter term they reserve for gas lpss
accompanying pressure reduction. There is a marked differ-
ence in the nature of gas emission in the two responses. On
sounding, sockeye smolts lost up to 72 per cent of swim bladder
gas and increased significantly in density in so doing. In the
"Gasspuck" reflex, fish emit gas in response to a reduction
in pressure only to the extent necessary to restore neutral
~·--.buoyancy.
Loss of gas on sounding was not the simple release of
gas held under pressure in the swim bladder. This was appar-
-
ent both from the negligible excess of pressure measured in
the b~adder ( 0. 2 mm Hg) and from the extent of gas lost on
sounding. A loss of 72 per cent of bladder gas would require
an excess pressure internally of almost 4 atmos. This
implied gas was expelled forcibly from the swimbladder by the
wall of the bladder or the body wall of the fish.
The adrenergic control of this expulsion was evident
from the effects of the sympathomimetic, ephedrine and the
adrenergic blocking agents, 11 dibenzyline" and "hydergine". The
former slightly enhanced gas loss on sounding, the latter
prevented it entirely. The behavioral response was otherwise
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unaffected by these agents. Expulsion of gas was due to the
contraction of the swimbladder and~ hence a reduction in its
cross-sectional area. This was clear from studies on both
isolated and intact swimbladders. Anesthetized smolts held
under water emitted gas on application of adrenaline in the
region of the swimbladder. Smolts in which the abdominal
musculature was opened mid-ventrally showed a marked con-
traction of the bladder with adrenaline.
Parasympathomimetics and cholinergic blocking agents
caused slight changes in the amount of .gas lost on sounding.
Because of the possible action of these agents at synapses
in sympathetic nerves, limited significance is attached to
these results.
The pressure necessary to force gas out through the
pneumatic duct averaged . :~8 .1 mm Hg for 30 smolts. That
this is an active constriction is indicated by the rapid de-
cline in duct-release pressure following the death of the
animal (Fig. 22}. The duct-release pressure of 11 dibenzyline"
blocked fish (26.8 mm Hg) did not differ significantly from
control fish. Hence sphincter contra:ction was not main-
tained by sympathetic nerves as suggested by Kuiper ( 1916)
and Franz (1937 ). Atropine on the other hand lowered duct-
release pressure to an average of 0.2 mm Hg, indicating
sphincter constriction was under cholinergic control. These
188 I
results agree closely with Fg_nge's demonstration of sphincter
closure with acetylcholine.
Reviews of gas emission accompanying pressure reduction
-·1
may be found in Jones and Marshall (1953} and Qutob (1962). .J
The argument of Rabaud and Verrier with Guyenot and Plat--l
tner, as to the origin of gas emitted with pressure reduction,
is discussed in the section on the effects of decompression
on fish.
Anatomical basis of pressure perception
Hasse (1873) first suggested that the funct~n of the
... -Weberian ossicles was to acquaint fish with the varying amount
of gas pressure within the swimbladde:r. Bridge and Haddon
( 1893 ) agreed with Hasse on the basis of their extensive
anatomical studies and the experiments of Charbonnel-Salle
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( 1887) • Deineka ( 1904) examined the wall of the carp swim-· ,
bladder and described nerve endings within the connective
tissue. Eissele ( 1922) described the histology of the bladder
wall of trout, perch, catfish and carp but did not stain
specifically for nervous tissue. Evans (1925) found three
layers of nerve cells and fibers in the roach swim bladder
wall. Fibrils penetrated into an inner layer of elastic tissue
and possibly to the epithelium. These being afferent fibers,
Evans suggested this was a receptor organ for the percep-
tion of pressure changes. Dotterweich ( 1932) suggested the
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189
ampullae of Lorenzini on the heads of ·sharks were hydrostatic-
pressure organs, but as Dijkgraaf ( 1941) pointed 9ut, there is
no experimental data to support such a suggestion.
More recently four studies have appeared describing
the innervation of the swim bladder. Scevola ( 1938) described
it briefly in the carp and Stefanelli ( 1946) in more detail for
the goldfish. The latter author concluded-:the afferent fibers
would be stimulated through distortion of the bladder wall.
Terio ( 1948) confirmed the presence in the bladder wall of
numerous nerve ganglia and nerves of somatic, parasympathetic
_and sympathetic origin.
Abraham and Stammer ( 1954) described a double in-
nervation in the wall of the carp swim bladder. They recog-
nized thin, sympathetic nerves with bipolar ganglia and con-
eluded these were vasomotor to the rich network of blood
vessels. The thicker, vagal sensory-fibres terminated as pres-
sure receptors in connective tissue of the submucosa. As
Qutob (1962) observed, Abraham and Stammer have not dem-
onstrated that these nerve endings are in fact pressure recep-
tors.
Jones ( 1958) concluded there was no evidence for a
pressure-sensory function in the swim bladder of physoclists.
In physostomes such a function may be involved in the release
of gas bubbles. In the Ostariophysi, the Weberian apparatus
190
may increase sensitivity of the swimbladder to changes in
pressure and thus make possible better control of gas entry
and loss.
It is noteworthy that other animals demonstrating a
pressure sensitivity may or may not make use of a gas phase
in doing so. Thus certain pressure-sensitive insects do
(Thorpe and Crisp, 1946) and marine crustaceanS' do not
utilize a gas bubbles in pressure perception, as shown by
Enright ( 1961) for the amphipod Synchelidium. This form
Enright found to be sensitive to 0. 01 atmos, equal to a
hydrostatic head of 4 in of water.
Neurophysiological studies
The pressure-receptor function of the swimbladder
was demonstrated by Koshtojanz and Vassilenko ( 1937). They
showed an increase in pressure in the carp swim bladder, equal
to 60 to 80 mm of water, induced strong swimming move-
ments by the fins plus reactions from respiratory muscles and
heart. The same response was elicited through stimulation
of the afferent vago-sympathicus nerve. Following section
of the; ·nerve, increased pressure in the bladder did not result
in any of these responses. Vasilenko and Livanov (1936)
extended the study of Koshtojanz and Vassilenko, recording
the impulses transmitted along the vago-sympathicus. Presum-
ably they continued . to_ use carp and bladder pressure changes
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191
were of the same order of magnitude. The recordings of
~-} Vassilenko and Livanov indicated rhythmic fluctuations in po-
]
tential and these changed with pressure increase or decrease
within the swim bladder. Increasing bladder pressure resulted
' 1 in an increase in high-frequency fluctuations. The authors
concluded the swimbladder was a receptive organ.
: 1 Long ( 1959) obtained changes in swim bladder volume
:J equal to 10-15 mm Hg, through electrical stimulation of the
tecti optici. These contractions were not due to the wall
~··· 1 of the swimbladder but rather by means of the musculature
J of the body cavity. The findings of Long are not in agree-
ment with Franz ( 1937) who showed gas emission in the min-
]' now was due to bladder contraction. In the present study
J 'lj
there appears little doubt that sockeye expell gas through a
reduction in the cross-sectional area of the swim bladder.
] Qutob . ( 1962) explored the sensitivity of the swim-
'l bladder and pneumatic duct by probing the surface and record-
1
ing action potentials along the vago-sympathicus. He con-
l
J eluded receptors of some kind were present along the wall
. -1 of the duct and some areas of the swim bladder in Leuciscus •
.J
Qutob repeated the experiment of Vassilenko and Livanov,
J again measuring action potentials along the vago-sympathicus
-L~/ ~ccompanying increase or decrease in pressure. Discharges
increased during pressure increase but the frequency of these
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192
impulses returned to normal when increase stopped. Pressure
release temporarily depressed discharges, followed by the nor-
mal pattern. Qutob (1962) repeated these measurements on
Scardinius exposed to pressure changes within a closed con-
tainer. Pressure increase of 25 mm Hg or decrease of 18
mm Hg resulted in doublfug and halving respectively the rate
of spontaneous discharge. These altered rates gradually
returned to the original level. Qutob concluded pressure per-
ception is achieved via the swimbladder wall.
Response to changes in barometric pressure
Fish culturists have long been aware of the changes
in the behavior of some fish accompanying changes' in the wea-
ther. Bert ( 1873) acknowledged the sensitivity of fish to
atmospheric pressure and reported Gobitus tenia may be kept
in an aquarium and serve as a barometer. Sagemehl ( 1895)
examined the swimbladder in a number of catfishes in which
the bladder extended through the lateral musculature and
terminated against·':the ·skin. He concluded that this arrange-
ment would limit the usefulness of the bladder in a hydro-
static role but would increase its sensitivity for perception
of pressure. Consequently Sagemehl advanced the hypothesis
that the Weberian apparatus was not concerned with report-
e_:. ing pressure and hence depth to the fish, but rather wtth
variations in atmospheric pressure which indicate weather
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193
changes. Sagemehl reserved proof of this hypothesis for a
later study on the Weberian apparatus. The author has been
unable to locate any such subsequent study.
Philippsen ( 1913) presented a superficial but poetic
account of fish responding to weather changes. He noted,
for example that pike, eels, perch and bream like to bite
before a thunderstorm, coincident with a fall in the barometer.
Philippsen also reported the erratic behavior of flounders in
estuaries of North Sea streams before poor weather or
thunderstoit"ms and associated this with low barometric pres-
sure.
Scheuring ( 1922) examined the swim bladder studies of
MUller, Weber, Hasse, Sagemehl, and others and concluded
that the two-compartment bladder represented the beginning
of a functional change. That is, a change from a more
primitive, hydrostatic apparatus to a purely hydrostatic or
better, barometric-perception organ. Scheuring noted the
swimbladder apparatus of the Cobitidae would permit these
fish to perceive the finest pressure variation and constitute
"weather fish". He obtained specific reactions from these
fish with pressure changes of 1/20 atmos.
Kyle ( 1926) noted fish such as leaches, with a "drum"
apparatus connected to the swim bladder, are very sensitive
to changes in atmospheric pressure and have been called
194
"weather fishes". He described anterior prolongations of the
clupeid swimbladder extending into the semicircular canals and
thus conveying differences in swimbladder pressure to the
endolymph. Kyle concluded this apparatus served as a man-
ometer or barometer.
Wunder ( 1936), in reviewing the functions of the
swim bladder, repeated the general observation that certain
fish react to barometric variations. He described as well
known the sensitivity of sheat fish and cyprinids to barometric
changes. Wunder added his personal observations of fish in
aquaria rising from the bottom and swimming about actively
on the approach of a thunderstorm. He was concerned with
the biological value of this sensitivity of bottom fish to
changes in barometric pressure and suggested it was assoc-
iated with food through the response of insects.
Recently two studies have appeared in which the
response of fish is related to barometric pressure. In each
case the relationship is supported, unlike earlier observations,
by data. Allen ( 1959) correlated the movement of chinook
and coho salmon into the fish way (University of Washington)
with eight environmental factors. Allen found a significant,
negative correlation for the entry of 82 chinook salmon with
barometric pressure; the value of -0.50 accounting for 25
per cent of the variability in the data. There are several
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195
objections to Allen's treatment of the data. Firstly, it is
not acceptable to conduct a large number of correlations and
then attach importance to one which proves significant. The
laws of chance permit occasional spurious correlations and
the chances of a 'significant' result increase with the number
of correlations attempted. Thus for eight correlations the
possibility of obtaining 1 per cent significance is not 1:100
but rather 1:12 1/2. SecondlY, the correlation is not limited
to the period when fish were entering the fish way, but
rather includes the 3 days of high barometric pressure before
any fish entered. Thirdly, Allen has not made clear whether
he considers all of the fish to be present when .t.he first fish
enters the fishway or whether the fish are arriving at the
fish way in a normal distribution. If the former is the case,
then the number of:'fish migrating must be weighted as to the
number available to migrate in response to changes in barometric
pressure. If the latter is the case, then barometric pres-
sure should be correlated with the:numbers migrating expressd
as a proportion of the current accumulated number of fish
available. Fourthly, while it is not completely clear from
the text, it appears that Allen correlated barometric pres-
sure and fish migration of the same day. The fish migrated
during the early morning hours and barometric pressure was
recorded at 0400, 1000, 1600 and 2200 hr and averaged.
Thus the correlation would be fish movement with barometric
p;ressure in the succeeding 24 hr. Fifthly, barometric pres-
sure does not fluctuate randomly from one observation to
the next and Allen· .does not appear to have eliminated this
effect of barometric pressure in determining subsequent
barometric pressure. As Moran ( 1949) pointed out, this
invalidates the use of "simple correlation 11 • Sixthly, Allen
does not described the demands which interpretation of pres-
sure change place on the fish. For example the peak migration
followed a fall in barometric pressure of 0.21 in Hg or a
__ reduction of 3 in or less in hydrostatic head. How does the
fish measure this? Because of the effects of waves, tides,
seiches, etc., pressure measurements of such small mag-
nitude could not be made at depth, but would have to be made
at the surface with the fish some fixed distance below the
meniscus. Also the fish would require an absolute pressure
sense on which to base a comparison. Response to falling
barometric pressure places even greater demands on the fish,
that is, measuring the rate of change in pressure. Thus
for Allen's data, the pressure decrease of 0.21 in Hg took
place over 42 hr, requiring the fish to measure a rate of
reduction of 0. 006 ft water per hr. That trout or salmon
are capable of doing so has yet to be demonstrated exper-
imentally. The available experimental evidence, to be sure,
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is to the contrary. Dijkgraaf ( 1943) showed blinded trout
could be conditioned to changes in hydrostatic pressure of 10
to 15 em of water, providing the fish was in physical con-
tact with the sides or bottom of the aquarium. Free-swim-
ming trout could not be conditioned to changes in pressure.
Dijkgraaf concluded the trout lacked a sense of hydrostatic
pressure.
More recently, Westman and Hoff ( 1962) examined
angling results for the bluefish ( Pomatomus saltatrix), the
fluke ( Paralichthys dentatus) and the porgy ( Stenotomus
-chyrsops) in the New York Bight. The authors concluded
that in all cases a singificantly greater number of fish per
angler -wer.e caught during days of below-average barometric
pressure than on days of above-average pressure. ~
objection must be raised here to what Westman and Hoff
termed 'average' barometric pressure. In this case they
chose 29.92 in Hg, the long-term meteorological average at
sea level. This had the effect of separating the data for
the bluefish into 9nialues .. of below and 43 above average.
This implies 29.92 in Hg has some significance to the fish.
Separating catch per angler on the basis of the average
barometric pressure during the period of study ( cf Westman
and Hoff) no difference was found between above and below-
average barometric pressure days ( t = 0. 58, to. 50 = 0. 69).
198
This was found also to be the case with the fluke and porgy
catches per angler. The significant differences claimed by
Westman and Hoff, using the lop-sided distribution about
29.92, are not s~n~icant for the average pressure over the
t period of study ( t = 1. 66, 0. 0 5 = 2. 03) •
In summary, the oft-repeated observations of fish
responding to change in barometric pressure leaves little
doubt that this may be possible for certain species, partie-
ularly those with a Weberian apparatus and living in shallow
aquaria. As yet, however, there appear to be no quanti-
tative measurements to establish this phenomenon beyond
doubt.
Perception of the small and gradual variations in bar-
ometric pressure places important demands on fish o In view
of this, considerable caution is warranted in granting all
species of fish the ability to respond to the slight changes
in pressure taking place in the atmosphere.
An examination of the problem of fish responding to
barometric pressure may be found in Bridge and Haddon
( 1893).
Pressure and Compensatory Swimming
Fishes with a swimbladder may undergo an appreciable
change in density with change in pressure. Pressure increase
results in compression of bladder gas, increased density and
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199
a tendency for the fish to sink, which is countered through
the fish swimming upward. The converse is true of a re-
duction in pressure. Baglioni ( 1908) noted this swimming
response in fish he pressurized experimentally. He concluded
the swim bladder wall was the sense-organ reflexly controlling
the described swimming movements. He based this opinion on
the knowledge that the swim bladder, being a gas-filled sac,
would undergo volume variations in relation to pressure, and
secondly Deineka ( 1904) had demonstrated already the pres-
ence of nerve endings in the bladder wall. As Jones {1958)
remarked, this is a very reasonable hypothesis but there is
little evidence to support it.
Kuiper {1915) adapted a perch to a pressure decrease
of 10 em Hg. Returned to atmospheric pressure, such a
fish then swims upward to avoid sinking. With an attached
cork the fish was drawn to the surface and attempted to
swim downward, the opposite direction which would be ex-
pected on the basis of Baglioni1s hypothesis. Qutob { 1962)
quotes Kuiper { 1914) as having demonstr-ated that carp,
tench, perch and leach show a fin response on pressure de-
crease which occurred before passive displacement. This
of course would tend to support Baglioni1s hypothesis.
Remotti { 1924) claimed to have proved the hypothesis
of Baglioni that tension in the bladder wall controlled reflexly
&@~ ~
200
the swimming activity. Remotti emptied physoclist swim-
bladders of air and refilled them with paraffin oil or water.
With an excess of pressure within the bladder, these fish
swam downward when of course they ought to have swum
upward. Remotti increased the hydrostatic pressure and
enhanced the downward swimming response, which result he
attributed to increased nerve impulses following bladder
expansion. Franz ( 193 7) noted this contradiction, pointing
out any change in response would require the swimbladder to
be partly filled with gas initially (presumably because of the
incompressible nature of liquids). If there was in fact gas
within the bladder, Franz continued, then increased pressure
would decrease the volume, relax the wall of the bladder and
thus induce the fish to swim upward. Franz offered the
explanation that the downward swimming observed by Remotti
was a flight response. Franz concluded Remotti's experiments
s'carcely can be considered as support for Baglioni1s fu.ypo-
thesis.
Franz ( 1937) quoted numerous authors who removed
swimbladder gas or the bladder itself and still observed nor-
mal swimming movements; he concluded that the swimbladder
alone could not be responsible for compensatory swimming.
Franz decompressed perch experimentally and recorded the
pressure reduction necessary to evoke compensatory swimming,
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201
then weighted the same fish and repeated the decompression.
Following weighting, compensatory swimming commenced at
a much greater reduction in pressure and hence greater
expansion of the bladder. Franz felt this argued against
perception by way of the bladder wall. Switching to min-
nows, Franz adapted the fish to a pressure reduction of
400 mm Hg, these physostomous fish expelling gas to achieve
buoyancy. When atmospheric pressure was restored the fish
were too dense but were rendered buoyant by air injected
into the body cavity. Thus in spite of the swim bladder volume
being greatly diminished the fish evidenced no compensatory
swimming or tendency to gulp air at the surface. Franz
concluded this ruled out the swimbladder wall of the minnow
as well as the perch as the site of perception involved in
compensatory swimming.
Koshtojanz and Vassilenko { 1937) recorded compen-
satory-swimming movements in response to pressure increases
in the swimbladder of carp. They describe the downward
movement of the tail and rotary movement of the pectorals,
typical of fish attempting to swim upward. Jones and
Marshall { 1953) pointed out the inconsistency in these obser-
vations. An increase in bladder pressure would be perceived
by the fish as a decrease in hydrostatic pressure and hence
the fish should tend to swim upward. Jones and Marshall
202
noted the fish were inverted and out of water and stimuli
from the labyrinth may have influenced the response.
Compensatory swimming accompanying a reduction in
pressure was quantified by Jones ( 1952) for the perch.
The reduction in pressure to which these fish were able to
compensate provided Jones with a measure of the upward
movement such fish can make without being buoyed to the sur-
face. Jones noted unpublished experiments indicating perch
do not respond to the stretching of the bladder wall nor did
blinding abolish compensatory swimming. Jones concluded this
left the labyrinth, sense orgarrs of the skin or the lateral
line as sites of stimulation.
McCutcheon ( 1958) described compensatory swimming
in the pinfish (Lagodon rhomboides) for both increased and
decreased buoyancy. Due to the position of the swim bladder
in this fish, pressure reduction resulted in the head tilting
upward. Compensatory movement of the pectoral fins coin-
cided with a tilt of 5 to 15°, rapid decompression evoking a
:Z.esponse at a lesser angle that a gradual reduction in pres-
sure. At neutral buoyancy pectoral fin beats were nil, but
on decompression rose to a maximum of 88 per min with an
increased amplitude. Increased pressure and hence negative
buoyancy induced pectoral rates as high as 114 per min with
the direction of pectoral thrusts opposite that with positive
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203
buoyancy. Fish in hydrostatic equilibrium and resting on the
bottom commenced compensatory movements of the pectoral
fins with a pressure change of 1-2 em water and before buoy-
ancy drift. Changes in swim bladder volume suggested a behav-
ioral sensitivity to pressure of 14.5 em water. The high
sensitivity of bottom-resting fish may be the result of tac-
tile stimuli, although McCutcheon appears to favor tension
receptors in the bladder. McCutcheon (1958, 1962) describes
small volume changes in the swimbladder of the pinfish result-
ing from muscular contraction and which he terms "compen-
· satory compensation".
In the present study, the results of the investig-
ation into compensatory swimming in young sockeye are dis-
cussed in relation to the behavior and vertical distribution of
this fish.
Pressure conditioning of fish
Dijkgraaf ( 1941) was able to train the minnow,
Phoxinus laevis either to an increase or decrease in pressur-e. of
0. 5 to 1. 0 em of water. This response was lost following
removal of the mallei bilaterally, with the minnows failing to
respond to pressure increases of as much as 40 em of water.
Dijkgraaf concluded the Weberian apparatus serves a hydro-
static function through perception of pressure change, in
204
addition to the accoustical function described by Frisch
and Stetter (1932) and others. Dijkgraaf (1943) attempted
to condition the physostomous trout to changes in hydrostatic
pressure. These fish responded to pressure increase or de-
crease of 10 to 15 em of water only if they were in physical
contact with some fixed object. Free-swimming trout failed
to respond to changes in pressure. Dijkgraaf concluded trout
lack a true hydrostatic pressure sense, as he had expected,
trout lacking the Weberian apparatus essential to pressure
sense. Qutob (1962) trained blinded minnows (~. laevis)
---Without mallei to respond to pressure changes of as little as
G . . 7 to 8 em of water. Based on the behavior of the fish,
Qutob believed the threshhold of perception of pressure change
was 5 to 6 em of water. This value agrees closely with the
pressure change of 5 em of water necessary to elicit a spon-
taneous response in non-conditioned fish. Comparing his
results on operated minnows with those of Dijkgraaf on intact
fish, Qutob concluded the Webericn apparatus made possible
perception of changes in pressure of 0. 5 or 1 to 5 em of
water. He concluded, nevertheless that the Weberian appar-
atus was not involved essentially in the maintenance of hydro-
static equilibrium through perception of changes in hydrostatic
pressure.
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Similar pressure conditioning experiments have yet to
be described for any of the species of Oncorhynchus. How-
ever, the inability of trout to train to a pressure change
over as many as 131 tests, as reported by Dijkgraaf (1942),
casts doubt on the possibility that Pacific salmon are capable
of detecting small changes in pressure.
The Effects on Fish of Positive and Negative Pressure
The effects of positive pressure
That some fishes are tolerant of high pressure is
----obvious from the great depths at which fish have been
recorded. For example, Marshall ( 1960) examined fish from
a depth of 5, 600 m which is equivalent to a pressure of
approximately 8, 500 psi. Experimental evidence suggests
pressure tolerance is not constant, but varies among species
of fish. Bert ( 1873) placed eels under a pressure of 10 to
15 atmos but observed their death only under conditions of
increased oxygen content. From the brief description of his
experiments it is doubtful that pressure per ~ caused the
death of the fish. Carbonnier ( 1873) examined the depths
and hence pressures inhabited by freshwater fish. The
Chicago Field ( 1879) carried an anonymous report of trout
passing through an inverted siphon "without inconveniences"
under a maximum pressure of 376 psi. Regnard ( 1884a)
206
observed fish could be subjected to 100 atmos with impunity
if lacking a swim bladder or if the bladder has been emptied.
A pressure of 200 atmos induced a reversible narcosis, and
300 atmos caused death. Regnard (1884b) extended h~ obser-
vations to marine fish and demonstrated narcosis in flatfish
after 10 min exposure to high pressures, prolonged to an hour,
death resulted. Gorham ( 1899), investigated the causes of
gas-bubble disease in fish and described the pressures at which
deep-sea fishes live. Melamphaes beanii, for example was
found at a depth of 2,949 fathoms and hence a pressure of
-----3.9 tons per sq in. Fontaine ( 1929 a and b) investigated the
et:fect of pressure on oxygen consumption by Pleuronectes
platessa. Oxygen consumption increased 58 per cent at a
press':l-re of 100 kg per em ( 97 atmos) and fish were killed at
145 atmos. Ebbecke ( 1935) studied the effect of high pres-
sure on a variety of marine animals. The rock-fish ( Gobius
niger) became more active at 50 atmos swam wildly at 100
atmos and soon died at a pressure of 200 atmos. A pressure
of 500 atmos immediately killed the rock-fish, flounder
(!:_. plates sa) and stickleback ( Spinachia vulgaris) • The fish
were stiff and crooked, the gills red, flared and congested.
Ebbecke suggested respiratory failure was due to disturbance
of the central nervous system and stiffening was due to
direct muscle stimulation. Very brief and incomplete reviews
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207
of the effects of pressure on fish may be found in Cattell
( 1936) and Hoff ( 1948). Hubbs and Rechnitzer ( 1952) in
studying the effect of explosion-induced pressures on fish,
subjected "fish" to positive pressures of 68 atmos briefly and
34 atmos for 12 hr with little immediate and no lasting ef-
feet e Row leg ( 1955) exposed rainbow trout to hydrostatic
pressures ranging from 50 to 200 psi for periods· up to 48
sec. The fish were immobilized. under pressure but resumed
·activity after decompression and showed no deterimental
effects during post-test observation. Muir ( 1959) in study-
ing the effects of pressure a:.nd decompression on coho finger-
lings, subjected fish to pressures of up to 110 psi, apparently
without ill effect.
Recently three studies have appeared by Bishai ( 1961
a, b, c) reporting the effects of pressure on fish e Bishai
( 1961a) after experimenting with Salmo salar and §.a trutta
concluded the effects of pressure depended on the age of
the fish. Yolk-sac alevins tolerated 5 atmos. Fi!'lgerlings
of both species, at an age of 98 to 179 days, died within 24
hr when subjected to an increase in pressure of more than
15 em Hg. This observation by Bishai was based on seven
experiments totalling eleven fish and hence requires verific-
ation. No suggestion was made as to the mechanism of action
of such slight ( 1/5 atmos) increase of pressure in causing
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208
the death of the fish. B ishai ( 1961 b and c) was able to
double, without effect, the pressure to which various Nile
fishes were adapted.
In the behavior portion of the present study, young
sockeye salmon were exposed to 300 psi ( 20 atmos) as emer-
gent fry and again at -3-month intervals during their first year
in fresh water. No lethal-pressure period was found such as
described by Bishai ( 1961a) for the Atlantic salmon and brown
trout. The series of tests in which sockeye smolts were placed
under a pressure of -~0 or 300 psi then released _to atmospheric
pressure resulted in a mortality sim_ilar to that of th_e control
groups (Fig. 31 and 32). T!J.us little or no adverse effect may
be associated with brief exposure to these relatively high pres-
sures.
The effects of negat~e pressures
The study of decompression probably began with the
classical experiments of Robert Boyle on press1:1re and volume,
respiration and combustion. Boyle ( 1670) reduced the pres-
sure on freshly drawn blood and noted the gas evolved. He
questioned whether the same was true of animals subjected to
rapid decompression:
Note, that the two foregoing Experiments were made
with an Eye cast upon the inquiry, that I thought might
be made; Whether, and how far the destructive oper-
ation of our Engin upon the included Animal, might be
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imputed to this, that upon the withdrawing of the
Air, besides the removal of what the Airs presence
contributes to life, the little bubbles generated upon
the absence of the Air in the Bloud, juyces, and soft
parts of the Body, may by their Vast number, and
209
their conspiring distention, variously streighten in some
places, and stretch in others, the Vessels, especially the
smaller ones, that convey. the Bloud and Nourishment;
and so by choaking up some; passages, and vitiating the
figure of others, disturb or hinder the due circulation
of the Bloud?
Boyle decompressed small animals and observed the appearance
of gas bubbles, thus confirming his suspicions.
Since Boyle, an extensive medical literature on decem-
_pression has grown out of th~ injuries and mortalities accom-
panying the use of caissons, diving gear and in connection
with high-altitude aviation. This has been reviewed in detail
by Hoff ( 1948). Two decompression effects in humans are
common in principle to fish and hence are described here.
"Lung burst" may result from the expansion of lung gas on
decompression. In this, alveoli are distended to the point of
rupture and air bubbles may enter broken blood vessels causing
air embolism (Duffner, 1960). Jones and Marshall ( 1953)
suggested this was a possible explanation of the symptoms
shown by fish raised to the surface from some depth. That
is, blood vessels of the swim bladder may rupture with dis-
tention and gas bubbles enter the blood str•eam. The second
analogous category of decompression effects is that of excess
nitrogen leaving solution within the animal and forming embolisms.
210
~t.
' -..
~ The associated pain and injury is known as "the bends" or
caisson disease (Behnke, 1955). Jones and Marshall examined
this possibility also and suggested the blood could become super-
saturated with swimbladder gas by way of the oval and that
subsequent pressure reduction would result in gas leaving sol-
ution and forming emboli.
Historically, the effects of d.ecompression on fish have
been investigated by a number of workers. Bert ( 1873) noted
eels decompressed after 3 days at 10 atmos soon died. This
he attributed to gas leaving solution in the blood and filling
the heart. Regnard ( 1884a) reported fish lacking a swim bladder
or first having the bladder emptied can be su.bmitted to a pres-
sure of 100 atmos and decompressed with impunity. He ob-
served, however, when this precaution was not taken the gas
within the swimbladder dissolved in the blood under this high
pressure and was liberated on decompression. The resulting
foam stopped the circulation and the animal died.
Gorham ( 1898, 1899) investigated the cause of gas
disease in marine fishes taken from deep water and placed in
an aquarium. He postulated the condition was due to swim-
bladder gas being forced out into the tissues or to dissolved
gases of the tissues leaving solution. Gorham was able to
induce the symptoms through decompression and aleviate the
disease by holding afflicted fish under a pressure of ZO ft of
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211
water. Gorham concluded the disease was understandable in
terms of simple physical laws.
Progress in the understanding of the effects of de-
compression was i:nterrupted by the work of Rabaud and
Verrier. Verrier ( 1931) disputed the swim bladder was of
value in swimming by experiments on bladder extirpation in carp,
tench and catfish. She ligatured the pneumatic duct of two
. carp and two tench, making, as she described it, physoclists
from physostomes; when decompressed these fish continued to
release gas • These results led Verrier to suggest the swim-
t • '·
_bladder was not involved in the response to variations in pres-
sure, in equilibrium and in vertical displacement as was believed
generally. These studies were repeated with the same result
on ot}?.er species ( Rabaud and Verrier, 1931), on 'fish from
which the swim bladder had been removed ( Rabaud and Verrier,
1934) and on bladderless fish (Rabaud and Verrier, 1932,1934).
Faced with the difficulty of explaining the damage along the
junction of swim bladder and musculature, Rabaud and Verrier
( 1935) concluded gas diffused through the wall of the swim-
bladder, filled the abdominal cavity and thus stretched the
lateral musculature on decompression.
The ligaturing of the pneumatic duct was promptly
repeated by Meierhans ( 1935 a, b), who found no such escape
of gas on decompression, but carp and roach in which the
212
duct was not tied released bladder gas on slight reduction in
pressure. In this latter case the bladder · was partially de-
flated when examined. Meier hans was of the opinion that
the bubbles appearing on the surface of the fish in the de-
compression experiments of Rabaud and Verrier did not orig-
inate from the tissues and blood but represented rather gas
leaving solution under reduced pressure.
Plattner ( 1937) also repeated these experiments and
concluded gas bubbles did originate from the swimbladder and
. passed out throug? the pneumatic duct. No bubbles were
______ emitted when the duct was ligatured and the bladder was de-
flated following decompression if the duct was not ligatured
(Plattner, 1938b). Guyenot and Plattner ( 1938, 1939)
raised a number of objections to the experimental procedures
of Rabaud and Verrier particularly in respect to the removal
of the swimbladder and the tendency of fish to swallow air
into the body cavity following such an operation.· Rabaud
and Verrier ( 1939) replied to Guyenot and Plattner but the
latter .authors had the last word in the review of swimbladder
function by Plattner ( 1941). This debate as to the function
of the swim bladder has been reviewed in detail by Jones and
Marshall ( 1953).
BaucUn ( 1937a) described an increase in erythrocyte
number in the perch, a~companying slight decompression while
~~
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213
oxygen content was held constant. Baudin ( 1937b) related
this to changes in swimbladder pressure and was able to
induce the erythrocyte change by altering the volume of bladder
gas. As yet there is no explanation of these results. Brown
( 1939) investigated the effect of decompression on swim bladder
inflation in the guppy. He found that below a critical range,
decompression favored the diffusion of gas into the swim-
bladder, resulting in bloating. Hogan ( 1940) examined fish
which had passed through a siphon at a vacuum of 18 to 26 in
Hg for 30 sec. Physostomous carp, catfish, minnows and gar
_____ .suffered little or no damage but physoclistous crappies, bass
and bluegills evide.nced ruptured bladders and hemorrhages.
Jones ( 1949) reported the fre_quency of ruptured swim-
bladders among perch trapped at depths to 60 :t:t, then rapidly
decompressed to atmospheric conditions. This was followed
(Jones, 1951) by a discussion of the restrictions a swim bladder
im:poses on the vertical movements of a fish and expressed in
an equation as the rate at which a physoclist is able to de-
compress without injury. Jones (1952) quantified these re-
strictions for the perch and showed that this fish was re-
stricted to a narrow zone above its plane of neutral buoyancy
equal to a one-sixth reduction in pressure.
Recently Bishai ( 1961a) reported the effects of de-
compression on young salmonids. He concluded alevins are
214
unaffected by decompression, the swimbladder being incompletely
developed at this stage. At an age of 56 days, decompression
did not result in gas emission and the bladder bloated. This
Bishai attributed to incomplete development of the sphincter
mechanism. Death of the young salmonids was associated with
the gaseous supersaturation of the experimental water, bubbles
of ·gas externally covering the fish and causing asphyxia.
Bishai raised the possibility of true decompression sickness
causing the death of the fish. Critically examining Bishai's
study, a number of objections must be raised to the procedure
_____ employed. Fish were held in static water and pressure was
maintained by means of an air lock over the water. This had
the effect of supersaturating the water, relative to atmos-
pheric pressure. Bishai occasionally measured the oxygen
content but this would provide a poor approximation of nitrogen
saturation (Harvey and Smith, 1961). While under pressure
the fish would tend to come to equilibrium internally with the
nitrogen content of their environment.
Thus on decompression there would be the marked ten-
dency of the now unstable nitrogen to leave solution within
the fish, coalesce to form bubbles and ultimately appear as
emboli. Also inherent in the design of the experiment was the
residence of the fish in supersaturated water on decompres-
sion. This leads, although seldom very rapidly, to the
~ 1
,-1 215
classical symptoms of gas disease (Marsh and Gorham, 1905,
~1 reviewed by Harvey and Smith, 1961). Thus Bishai's fish
' l could have been afflicted in this way. Yet another cause of
gas disease is that already referenced to Jones and Marshall
' l ( 1953), that is, the entry of swimbladder gas into the cir-
' l culation of the fish on decompression either by diffusion while
in solution or directly as bubbles entering ruptured vessels.
'I In view of the air lock available under pressure and the ten-
] dency of such physostomes to inflate their swimbladders to
neutral buoyancy, the latter explanation appears the most
] ---~likely for Bishai's results. Bishai ( 1961) repeated the decem-
f~'" '1i pression studies on several Nile River fishes and in this series
he attributed the death of the fish to gas disease brought
J on by the supersaturated water at the end of decompression.
: J
The symptoms accompanying death, darting and bending,
resemble much more those accompanying emboli originating from
J swim bladder gas.
l Cyclical pressure changes
1
Under certain conditions fish may be subjected to both
pressure increase and decrease within a short period of time.
This occurs during the passage of fish through hydro-electric
J-~., '\_~"<-~
turbines and where fish are in close proximity to underwater
explosions. That these cyclical pressure changes may be harm-
.J ful to fish is well known. However, the complexity of the
J
216
pressure increase and decrease and other pressure-related
phenomena, such as cavitation, make difficult the isolation of
the deleterious component. In the subsequent two sections
the literature is reviewed for fish passage through turbines
and underwater explosions and discussed in relation to the ef-
fects of pressure increase and decrease on fish, as found in
the present study.
Discussion here will be limited to the reaction-type
turbines, as . opposed to impulse turbines, passage of fish is not
a consideration with the latter. Generally fore bay water
. enters the penstock at some appreciable depth below the sur-
face. The penstock leads downward terminating at the runner r
under conditions of maximum positive pressure. Pressure falls
rapidly as the water passes across the blade of the runner,
the decrease taking place in a fraction of a second. Within
the draft tube below the runner the pressure may be above
or below atmospheric depending on the !J:eight of the tailrace
water. Thus fish passing through turbines may be subjected
to very different conditions of pressure increase and decrease,
depending on:
i. the height of the dam and hence depth of the
reservoir.
ii. the depth of the penstock below the surface.
iii. the magnitude of the positive or negative pres-
sure in the draft tube.
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217
iv. the efficiency at which the turbine is operating.
v. the propensity of the design to produce cavit-
ation •
In addition the effects of these factors will vary depending on
the condition of the fish:
i. whether the fish are physostomous or physoclistous.
ii. whether the fish were residing at depth or had
sounded from the surface to enter the penstock.
iii. the degree of swim bladder inflation.
iv. the dissolved gas content of the fish passing
through the turbine •
v. for species of physostomous fish, the morphology
of the pneumatic duct and its relative patency for
gas emission.
vi. the age, size and relative healthiness of the fish.
The increase in positive pressure accompanying passage
th;roough the penstock has seldom been considered of importance
to the fish. Thus for low-head dams of 100 ft or so, the
depth and pressure, would be in keeping with the known ver-
tical distribution of species such as sockeye. Schoeneman
and Junge ( 1954) assessed the mortality at a 100 ft (lower
Elwha) and 194 ft (Glines) dam. ,The latter showed a mor-
tality of 33 per cent compared to nil for the former, other
conditions being relatively equal. The authors concluded the
218
difference in survival rates was a function of hydrostatic head
and hence pressure differences~ the critical head being be-
tween 100 and ZOO ft o In support of Schoeneman and Junge,
measurements at low-head dams (Big Cliff, Bonneville, Mct'Jary)
have shown rela~ively low mortalities, whereas studies at high
dams (Baker, Puntledge, Shasta) have evidenced mortalities
similar to that of the Glines o In the present study fish sub-
jected to 680 ft of hydrostatic head (Fig. 31) and 100 ft of
head (Fig. 32), then released to above or below atmospheric
pressure, showed very similar effects and losses. It is con-
~~-~~-eluded therefore that some factor associated with hydro-
static head, but other than positive pressure, is responsible
for the variable death of fish in the turbines of low and
high-head dams o
That negative pressures in the draft tube could injure
or kill fish is apparent from the literature on the effects of
decompression on fish (Bert, 1873; Gorham, 1898; Baudin,
1937; Hogan, 1941). Experimentally this was shown to be
the case by Cramer ( 1960) in model studies using physoclis-
tous smallmouth bass. Mortalities increased as draft-tube
pressures were reduced below atmospheric. Muir ( 1959) on
exposing fingerling coho salmon to a sudden reduction in
pressure from as high as 110 psi to a 29 in Hg vacuum,
found little mortality. He concluded from this significant
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mortality is unlikely to result from exposure to a partial
vacuum in the absence of cavitation. Corps of Engineers ( 1960)
decompression tests on salmon fingerlings resulted in "heavy
mortality" only if the pressure reduction was rapid and the
fish were allowed an air lock under pressure. Such fish were
described as being "pressure accommodated". From witness-
ing a subsequent test it was apparent that the fingerling
salmon were inflating their swimbladders to neutral buoyancy
with atmospheric air while under pressure. On sudden reduc-
tion in pressure such fish were unable to emit the then excess
______ gas. The result was the rapid death of the fish, probably
due to embolisms resulting from swimbladder gas passing into
the tissues or ruptured blood vessels, as described by Jones
and Marshall ( 1953) o In addition the water containing the
fish was greatly in excess of air saturation o The fish would
be in gaseous equilibrium with this water and on pressure
reduction would become supersaturated temporarily. Thus the
fish could have died from gas disease or. "the bends" quite
independent of swim bladder gas. The present study has shown
decompression may or may not have serious consequences,
depending on the magnitude of the vacuum, the condition of
the fish and physical factors in the environment of the fish.
An aspect of pressure changes within turbines is the
phenomenon of cavitation. In this condition 1 water-vapor
~ ~ bubbles form, then collapse or implode, primarily in the area
of low pressure along the runner. This is accentuated by a
negative pressure in the draft tube. Experimental cavitation
studies by the Corps of Engineers ( 1957), employing a ven-
turi with pressures as low as a 28 1/2 in Hg vacuum, showed
a maximal mortality of 8 per cent. Muir ( 1959), on the
results of his experimental studies of decompression and cav-
itation, was led to conclude that cavitation in turbines was
the more important factor involved in fish mortalities. Cav-
itation tends to increase as runner efficiency declines, leading
to the common belief that Kaplan (adjustable blade) . turbines
would result in lower mortalities than the Francis type.
Cramer's ( 1960) model studies showed no difference in mor-
talities between the two types. Cramer and Oligher ( 1961)
concluded (in so far as pressure considerations are concerned)
..
the adverse effects of turbines could be minimized by oper-
ation at high efficiency and having the runner submerged in
the tailwater. This would reduce cavitation on the runner
and negative pressures in the draft tube.
Physical and biological factors involved in the mortality
of fish in relation to dams have been analyzed recently by
Andrew and Geen ( 1960) and Lucas ( 1962)
Underwater explosions may be considered a special
case of pressure and pressure change and are discussed here
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221
only insofar as they apply to the effects of pressure on fish.
The complex physics of underwater explosions has been des-
cribed in detail by Cole ( 1948). The magnitude of the pres-
sure wave depends on the size and nature of the explosion and
diminishes as the third power of the distance from the center.
The wave of rarefaction is more marked close to the water
surface. Gowanloch and McDougall ( 1946) measured a com-
pression-wave duration of five one-thousands of a second
followed by a negative-pressure phase of twenty-five one-
thousands of a second. These authors concluded damage oc-
curs at a critical pressure of 500 psi, when this wave crosses
the phase boundary of fluid tissues to swimbladder gas. Under
these conditions "shredding" takes place and results in hem-
orrhagic lesions. Alpin ( 194 7) confirmed the rupturing of the
bladder and noted bladderless sculpins were unaffected by
underwater explosions. Fitch and Young ( 1948) concluded each
species of fish has a specific resistance to shock pressure.
Barracuda have a cylindrical body, a tough, heavy-walled swim-
bladder and have more resistance to pressure than laterally
compressed fish, such as the saltwater perch, with a thin-
walled bladder. Coker and Hollis ( 1950) examined fish injured
or killed in marine underwater explosions and invariably found
the swimbladder ruptured with some degree of vascular hem-
orrhage within the bladder. Hubbs and Rechnitzer ( 1952)
established the lethal threshhold for dynamite explosions at
40 to 70 psi, the lower threshhold being due to the very
rapid rate of pressure change. Fish mortalities were greater
close to the water surface, possibly due to the rarefaction
wave. This is formed as a compression rw.ave arrives at the
air-water interface, is reflected downward and soon can-
celled by the increasing hydrostatic pressure.
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LITERATURE CITED
l
224
LITERATURE CITED
-i
-j
Abraham, A. and A. Stammer~ 1954 Pressoreceptoren in der
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Alexander, R. MeN. 1959b. The densities of Cyprinidae.
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Alexander, R. MeN. 1959c. The physical properties of tlf~ -"' "--'
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Allen, G.H. 1959. Behavior of chinook and silver salmon.
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____ Alpin, J .A. 1947. The effect of explosives on marine life
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< 1
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-l
-I
c l
]
]
. I
,]
Franz, G. 1937. Uber den Reflex des Gasspuckens bei
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C_, __
'•·
.... _.-_:....
APPENDICES
241
APPENDIX A
' l
Theoretical Considerations
The solubility of a gas in a liquid has a finite value
dependent on the nature of the gas, of the liquid and on the
'] pressure and temperature o The solubility of a gas is usually
expressed as the absorption coefficient, which is defined as
1 j the volume of gas, reduced at 0 oc and 1 atmos dissolved
by unit volume of solvent at the temperature of the exper-
iment and under a partial pressure of the gas of 1 atmos
' l
.J ____ (Gladstone , 1946) o Where V D is the volume of dis solved gas
reduced to conditions of standard temperature and pressure,
V is the volume of the liquid and P is the partial pressure of
the gas in atmospheres, then the absorption coefficient ( o< )
is equal to
o(= v p
I
J
Pressure is the most important factor affecting the
j
. J solubility of gases. This is stated in Henry's Law: the mass
·-·of gas dissolved by a given volume of solvent, for a constant
temperature is proportional to the pressure of the gas with
which it is iinequilibrium. This may be expressed by the form-
ula
M=kxJ?
. J
242
where M is the mass of gas dissolved by unit volume of
liquid,
k is a constant and
P ·is the pressure in atmospheres o
The effect of pressure in reducing oxygen saturation is shown
in Fig. 46.
Temperature is another factor influencing the solubility
of gases in liquids o In the case of oxygen and nitrogen, sol-
ubility in water decreases rapidly with increasing temperature.
The change in solubility is not quite linear as shown in Fig.
__ .47, nor is it the same for the two gases.
The partial pressure of a gas is defined as the pres-r·
sure each gas would exert if it alone occupied the volume of
a mixture of gases at the same temperature. This is expres-
sed in Dalton's Law of partial pressures: the total pressure
of a mixture of gases is equal to the sum of the partial
pressures of the constituent gases. Dalton showed that in
a mixture of gases each constituent dissolves according to its
own partial pressure, or simply that Henry's Law applies to
each gas independent of the pressure of the other gases.
For dry air free of carbon dioxide and a total pressure of
760 mm Hg, the fractional composition and partial pressures
of the principle gases are:
]
l
J
~,j
JC
J
J
z
0 ...
4(
0::
140
130
120
110
\ ~ 90
.cr
(I) 80 ... z
""' ~~u
30
20
10
0~----~----~----L-----~----~----~----L-----L-----L---~
0 2 3 4 ~ 6 7 8 9 10
PRESSURE IN ATMOSPHERES
0 68 102 136 170 203 237 271 305
DEPTH IN FEET
Figure 46. Per cent saturation in relation to pressure and dc·pth.
Absolute sat~uration of Ricker ( 1<334).
•
., ... . .
244
25~--------------------------------------------------~
10 15 20
TEMPERATURE IN DEGREES CENTI~RAOE
Figure 4 7. Oxygen and nitrogen content of air-equlllbrated
water, 0 to )0°C.
•
30
:_.:-' · .. =·'/of.,,
~l
I
I
' !
.. l
~-
. -~
l
~ 1
J
]
, .... 1~ l'ZW
J
]
J
: j
J
J
245
nitrogen 0.7811 593.6 mm Hg
oxygen 0.2095 159.2 mm Hg
argon 0.0094 7.2 mm Hg
These gases dissolve _ in relation to solubilities, as expressed
by the absorption coefficients and in relation to the partial
pressures. Thus at a temperature of ooc, the three gases
will enter solution in water from air in the ratios of:
nitrogen 0.7811 X 0.02354 = 0.018387
oxygen 0.209 X 0.04889 = 0.0~0242
argon 0.0094 X 0.0578 = 0.000543
----Thus oxtzgen, which is only one-quarter as plentiful as nitro-
gen in ai.r, being twice as soluble as nitrogen, becomes one-
half as plentiful as nitrogen in water which is in equilibrium
with a large volume of air. Hence the percentage composition
of oxygen increases from 21 per cent in air to approximately
84 per cent in water. Hereafter argon will not be treated
separately but rather included with nitrogen, as is commonly
done, under the term "atmospheric nitrogen" consisting by
volume of 98.815 per cent nitrogen and 1.185 per cent
argon (Handbook of Chemistry and Physics, 1958). The air
fraction of "atmospheric nitrogen" becomes 0. 7905 and exerts
a partial pressure of 600.8 mm Hg.
In considering a gas or mixture of gases in equilibrium
with a solvent it is necessary to have regard for the solvent
·~ t .
::..·.
246 l
which is in the gaseous state. In the case of air over water,
the total pressure of the mixture of gases is equal to the
partial pressures of the individual gases plus the partial pres-
sure of the water vapor. At any given temperature the pres-1
sure of the water vapor in equilibrium with liquid water is a
constant quantity, termed the aqueous or water vapor pres-
sure. The vapor pressure of a liquid increases with rising
temperature and the increase becomes rapid as the temperature
approaches the boiling point. The aqueous vapor pressure
over water is given for temperature from 0 to 100 °C in
Table VII. At ooc water vapor pressure is 4.6 mm Hg or
0. 6 per cent of 1 atmos, thus failing to correct for water
vapor pressure would invoke an error of 0. 6 per cent at this
temperature. At 25°C the water vapor pressure is 23.8 mm
Hg and constitutes 3 .1 per cent of atmospheric pressure.
Thus an appreciable error results if water vapor pressure is
not taken into account in calculating gas tensions.
In the present study, oxygen and nitrogen solubilities
were calculated from the absorption (Bunsen) coefficients
( o( ) as found in the Handbook of Chemistry and Physics.
The oxygen fraction of air was taken as 0.2095 as recom-
mended by Hutchinson { 1957). Correcting for water vapor
pressure the solubility of oxygen is air-equilibrated water was
calculated for each 0.1 oc· from 0 to 30 °C. Thus oxygen
~ J
I
~ j
~,
rl 247
~~ -;
TABLE VII
rl
Water vapor pressure in mm Hg for temperatures of
0 to 100 degrees Centigrade
~ -1
Temp. W.V.P. Temp. w.v.P. Temp. w.v.P. Temp. W.V~P.
-1 0 4.
1 4.9 26 25.2 51 97.2 76 301.4 ;,;·~·
'1 2 5.3 27 26.7 52 102.1 77 314.1:
3 5.7 28 28.3 53 107.2 78 327.3
4 6.1 29 30.0 54 112.5 79 341.0
] 5 6.5 30 31.8 55 118.0 80 355.1
6 7.0 31 33.7 56 123.8 81 369.7
J 7 7.5 32 35.7 57 129.8 82 384.9
8 8.0 33 37.7 58 136.1 83 400.6
9 8.6 34 39.9 59 142.6 84 416.8
J 10 9.2 35 42.2 60 149.4 85 433.6
36 44.6 61 156.4 86 11 9.8 450.9
]0 12 10.5 37 47.1 62 163.8 87 468.7
13 11.2 38 49.7 63 171.4 88 487.1
14 12.0 39 52.4 64 179.3 89 506.1
] 15 12.8 40 55.3 65 187.5 90 525.8
16 13.6 41 58.3 66 196.1 546.1 91
-, 17 14.5 42 61.5 67 205.0 92 567.0
18 15.5 43 64.8 68 214.2 93 588.6
19 16.5 44 68.3 69 223.7 94 610.9
J 20 17.5 45 71.9 70 233.7 95 633.9
21 18.7 46 75.7 71 243.9 96 657.6
~~ 22 19.8 47 79.6 72 254.6 97 682.1
23 21.1 48 83.7 73 265.7 98 707.3
24 22.4 49 88.0 74 277.2 99 733.2
~ I -25 23.8 50 92.5 75 289.1 100 760.0
J
t,~
'----_ ·.-..:f;
\_S,'"'
J
J
solubility was calculated in ml per liter from:
o{x 0.2095 x 760-!LV.v.p.
760
248
The resulting values appear in Table VIII. The solubility of
oxygen in mg per liter (parts per million) was calculated as
above and an oxygen density of 1. 429 mg per mi.
o{ X 0.2095 X 760 -W.V.p. X 1.429
760
The resulting values appear in Table IX.
Nitrogen solubilities were calculated similarly from the
absorption coefficients, Handbook of Chemistry and Physics.
The nitrogen fraction of the air, inclusive of the noble gases,
was 0. 7905. Correcting for water vapor pressure, the
solubility of nitrogen in ml per liter of air-equilibrated water
becomes:
o{x 0.7905 x 760-w.v.p. (Table X).
760
Nitrogen solubility in mg per liter (parts per million) was
obtained by correcting for the density of the gas (i.251 mg
per ml).
o(x 0.7905 x 760-w.v.p. x 1.251 (Table XI)
l
" 1
-J
_1
J
-l
-l
760 -1
~~
~~ 249
TABLE VIII
~-, Solubility of oxygen, from a wet atmosphere at a pressure
of 760 mm Hg, in ml per liter at temperatures ,,,
from 0 to 30°C
~ l Temp. o.o 0.1 0.2 0.3 0.4 0.5
,-1 0 10.17 10.14 10.11 10.08 10.06 9.93
1 9.90 9.85 9.85 9.82 9.79 9.76
2 9.64 9.61 9.59 9.56 9.53 9.50
: l 3 9.38 9.35 9.33 9.30 9.28 9.25
4 9.13 9.10 9.08 9.05 9.03 9.01
5 8.89 8.87 8.85 8.82 8.80 8.77
J 6 8.66 8.64 8.62 8.60 8.59 8.56
7 8.47 8.45 8.43 8.40 8.38 8.35
J 8 8.24 8.23 8.21 8.19 8.17 8.15
.. 9 8.05 8.03 8.01 7.99 7.98 7.96
10 ·7.86 7.84 7.82 7.80 7.79 7.77
11 7.69 r;,.67 7.66 7.64 7.62 7.60
12 7.52 7.50 7.48 7.46 7.45 7.43
]· 13 7.34 7.32 7.31 7.29 7.28 7.26
14 7.19 7.17 7.16 7.14 7.13 7.11
15 7.04 7.02 7.01 6.99 6.98 6.96
J 16 6.89 6.87 6.86 6.84 6.83 6.81
17 6.74 6.72 6.71 6.69 6.68 6.67
__]
18 6.60 6.58 6.57 6.56 6.55 6.53
19 6.47 6.46 6.45 6.43 6.42 6.41
20 6.35 6.34 6.33 6.31 6.30 6.28
-l
. J 21 6.21 6.20 6.19 6.18 6.17 6.15
22 6.10 6.08 6.07 6.06 6.05 6.04
J 23 5.97 5(.96 5.95 5.94 5.93 5.91
24 5.86 5.85 5.84 5.82 5.81 5.80
25 5.74 5.73 5.72 5.71 5.70 5.69
J 26 5.63 5.62 5.61 5.60 5.59 5.58
27 5.53 5.52 5.51 5.50 5.49 5.48
'h~ 28 5.42 5.41 5.40 5.39 5.38 5.38
29 5.33 5.31 5.30 5.29 5.28 5.27
30 5.23 5.22 5.21 5.20 5.19 5.18
J ...
J
(i 250
~
TABLE VIII (continued)
Temp. 0.6 0.7 0.8 0.9
0 10.01 9.98 9.95 9.92
1 9.74 9.71 9.69 9.66
2 9.48 9.45 9.43 9.40
3 9.22 9.19 9.17 9.15
4 8.99 8.99 8.94 8.91
5 8.75 8.73 8.71 8.68
6 8.54 8.52 8.51 8.49
7 8.33 8.31 .8.29 8.27
8 8.13 8.11 ·8.10 8.07
9 7.94 7.92 7.90 7.88
10 7.76 7.74 7.73 7.71
11 7.59 7.57 7.55 7.53
12 7.41 7.39 7.38 7.36
--13 7.25 7.23 7.21 7.20
~r! 14 . 7.10 7.08 7.07 7.05
~~ 15 6.95 6.93 6.91 6.90 r-··
16 6.79 6.78 ( 6.77 6.75
17 6.66 6.64 6.63 6.61
18 6.52 6.51 6.50 6.48
19 6.40 6.39 6.38 6.36
20 6.27 6.25 6.24 6.22
21 6.14 6.13 6.12 6.11
22 6.03 6.01 6.00 5.98
23 5.90 5.89 5.88 5.87
24 5.79 5.77 5.76 5.75
25 5.68 5.66 5_.65 5.64
26 5.57 5.56 5.55 5.54
27 5.47 5.45 5.44 5.43
28 5.37 5.36 5.35 5.34
29 5.27 5.26 5.25 5.24
30 5.17 5.17 5 ... 16 5.16
~1
c)(jj 251
-4~ ... TABLE IX
-1
Solubility of oxygen, from a wet atmosphere at a pressure
of 760 mm Hg, in mg per liter at temperatures
~ l from o to 30°C
J Temp. o.o 0.1 0.2 0.3 0.4
0 14.53 14.49 14.45 14.41 14.37
J 1 14.14 14.10 14.07 14.03 13.99
2 13.77 13.74 13.70 13.66 13.62
3 13.40 13.36 13.33 13.29 13.26
: 1 4 13.04 13 .oo 12.97 12.94 12.91
5 12.71 12.68 12.64 12.61 12.58
~ l 6 12.38 12.35 12.32 12.30 12.27
7 12.10 12.07 12.04 12.01 11.98
8 11.79 11.76 11.73 11.71 11.68
"j 9 11.51 11.48 11.45 11.43 11.40
-----10 11.23 11.21 11.18 11.16 11.13
11 10.99 10.97 10.94 10.92 10.89
12 10.74 10.72 10.69 10.67 10.64
13 10.49 10.47 10.45 10.42 10.40
~1 14 10.27 10.25 10.23 10.21 10.19
15 10.06 10.04 10.02 9.99 9.97
-J 16 9.84 9.82 9.80 9.78 9.76
17 9.63 9.61 9.59 9.57 9.55
18 9.43 9.41 9.39 9.38 9.36
: I
;19 9.25 9.23 9.22 9.20 9.18
20 9.08 9.06 9.04 9.02 9.00
: j
21 8.88 8.86 8.85 8.83 8.82
22 8.72 8.70 8.68 8.66 8.64
23 8.53 8.51 8.50 8.48 8.47
"I
--24 8.37 8.35 8.34 8.32 8.30
25 8.20 8.19 8.17 8.16 8.14
J 26 8.05 8.04 8.02 8.01 7-99
27 7.90 7.89 7.87 7.86 7.84
28 7.75 7.74 7.72 7.71 7.69
J 29 7.61 7.60 7.58 7.57 7.55
30 7.47 7.46 7.44 7.43 7.42
\.:_" -
J
,__l
Temp.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
TABLE IX
14.34
13.96
13.59
13.22
12.88
12.55
12.24
11.95
11.65
11.37
11.11
10.87
10.62
10.38
10.17
9.95
9.74
9.53
9.34
9.17
8.98
8.80
8.63
8.45
8.29
8.13
7.98
7.83
7.68
7.54
7.41
0.6
14.30
13.92
13.55
13.18
12.84
12.51
12.21
11.91
11.62
11.34
11.09
1.0 .84
10.59
10.36
10.14
9.93
9.71
9.51
9.32
9.15
8.96
8.78
8.61
8.43
8.27
8.11
7.96
7.81
7.67
7.53
7.39
(continued)
0.7
14.26
13.88
13.51
13.15
12.81
12.48
12.18
11.88
11.59
11.31
11.06
10.82
10.57
10.34
10.14
9.91
9.69
9.49
9.30
9.13
8.94
8.77
8.59
8.42
8.25
8.10
7.95
7.80
7.65
7.51
7.38
0.8
14.22
13.84
13.47
13.11
12.78
12.45
12.16
11.85
11.57
11.29
11.04
10.79
10.54
10.31
10.10
9.88
9.67
9-47
9.29
9.11
8.92
8.75
8.57
8.40
8.23
8.08
7.93
7.78
7.64
7.50
7.37
0.9
14.18
13.81
13.44
13.08
12.74
12.41
12.13
11.82
11.54
11.26
11.01
10.77
10.52
10.29
10.08
9.86
9.65
9.45
9.27
. 9.10
8.90
8.74
8.55
8.39
8.22
8.07
7.92
7.77
7.62
7.48
7.35
252
~1
'j 253
TABLE X
] Solubility of nitrogen, from a wet atmosphere at a pressure
of 760 mm Hg, in ml per liter at temperatures
] from 0 to 30°C
~J Temp. o.o 0.1 o.z 0.3 0.4
0 18.50 18.45 18.40 18.36 18.31
] 1 18.03 18.00 17.95 17.91 17.86
z 17.59 17.55 17.51 1?".-47 17.42
3 17.15 17.11 17.07 17.03 16.99
J 4 16.73 16.69 16.65 16.61 16.57
5 16.34 16.30 16.26 16.22 16.18
J 6 15.94 15.90 15.87 15.83 15.80
7 15.57 15.54 15.50 15.47 15.43
8 15.21 15.17 15.14 15.10 15.07
'] 9 14.86 14.83 14.79 14.76 14.72 -___ .. 10 14.52 14.49 14.46 14.43 14.40
:J-11 14.23 14.19 14.16 14.13 14.10
12 13.92 13 .8.9 1J .86 13.93 13.80
13 13.62 13.59 13.57 13.54 13.52
~-1 14 13.36 13.33 13.30 13.27 13.25
15 13.09 13.07 13.05 13 .oz 12.99
--J 16 12.84 12.81 12.79 12.76 12.74
1-7 12.60 12.57 12.55 12.52 12.50
18 12.37 12.34 12.32 12.39 12.27 ., 19 12.13 12.11 12.09 12.07 12.05
'-j zo 11.91 11.89 11.87 11.85 11.84
:1 21 11.73 11.71 11.69 11.67 11.65
zz 11.51 11.49 11.48 11.46 11.45
23 11.33 11.31 11.29 11.27 11.26
' j
----24 11.15 11.13 11.12 11.10 11.09
25 10.99 10.97 10.95 11.93 10.91
.J 26 10.80 10.78 10.77 10.75 10.74
27 10.64 10.62 10.61 10.59 10.58
28 10.48 10.46 10.45 -10.43 10.42
c~ 29 10.31 10.29 10.28 10.26 10.25
30 10.16 10.14 10.13 10.11 10.10
··~:rs
-I
J
254 1
TABLE X (continued} 'J
Temp. 0.5 0.6 0.7 0.8 0.9
0 18.27 18.22 18.17 18.13 18.08
1 17.82 17.77 17.73 17.68 17.64
2 17.38 17.33 17.29 17.24 17.20
3 16.95 16.90 16.86 16.82 16.77
4 16.54 16.50 16.46 16.42 16.38
5 16.14 16.10 16.06 16.02 15.98
6 15.76 15.72 15.68 15.64 15.61
7 15.40 15.36 15.32 15.28 15.25
8 15.03 15.00 14.96 14.93 14.89
9 14.69 14.65 14.68 14.59 14.55
10 14.37 14.34 14.31 14.28 14.25
11 14.07 14.04 14.01 13.98 13.95
12 13.77 13.74 13 .• 71 13.68 13.65
13 . 13.49 13.46 13.43 13.41 13.38
~ 14 13.22 13.20 13.17 13.13 13.12 r
.
15 12.96 12.93 12.91 12.89 12.86
16 12.71 12.69 12.67 12.65 12.62
17 12.47 12.45 12.43 12.41 12.39
18 12.24 12.20 12.20 12.18 12.16
19 12.02 12.00 11.98 11.96 11.93
20 11 .• 82 11.80 11.78 11.76 11.74
21 11.62 11.60 11.58 11.56 11.53
22 11.43 11.41 11.39 11.37 11.35
23 11.22 11.22 11.20 11.19 11.17
24 11.07 11.06 11.04 11.02 11.00
25 10.89 10.88 10.86 10.84 10.82
26 10.72 10.70 10.68 10.67 10.65
27 10.56 10.54 10.52 10.51 10.49
28 10.40 10.38 10.36 10.34 10.32
29 10.23 10.22 10.20 10.19 10.17
30 10.08 10.07 10.05 10.04 10.02
1
'~1 255 -@I
';, TABLE XI
~ 1
c j Solubility of nitrogen, from a wet atmosphere at a pressure
:-'1
of 760 mm Hg, in mg per liter at temperatures
from 0 to 30°C
~ 1 Temp. o.o 0.1 0.2 0.3 0.4
0 23.14 23.08 23.02 22.97 22.91
r 1 1 22.56 22.51 22.45 22.40 22.34
2 22.01 21.96 21.90 21.85 21.79
3 21.46 21.41 21.35 21.30 21.25
' 1 4 20.93 20.88 20.83 20.78 20.73
5 20.44 20.39 20.34 20.29 20.24
] 6 19',.94 .· 19.89 19.85 19.80 19.76
7 19.48 19.54 19.39 19.35 19.30
8 19.03 18.99 18.94 18.90 18.85
' J 9 18.59 18.55 18.50 18.46 18.42
--~-10 18.16 18.12 18.09 18.05 18.02
~~ ..--~ ~~~·
17.76 17.68 17.64 ~ 11 17.80 17.72
c 12 17.41 17.37 17.34 17.30 17.26
13 17.04 17.01 16.97 16.94 16.91
] 14 16.71 16.68 16.64 16.61 16.58
15 16.38 16.35 16.32 16.28 16.25
~J 16 16.06 16.03 16.00 15.97 15.94
17 15.76 15.73 15.70 15.67 15.64
18 15.47 15.44 15.41 15.38 15.35
-J 19 15.18 15.15 15.12 15.10 15.07 J 20 14.90 14.88 14.85 14.83 14.81
1 21 14.67 14.64 14.62 14.59 14.57
22 14.41 14.39 14.36 14.34 14.32
23 14.18 14.16 14.13 14.11 14.09
:J
-----24 13.95 13.93 13.91 13.89 13.87
25 13.75 13.73 13.70 13.68 13.65
J 26 13.51 13.49 13.47 13.45 13.43
27 13.31 13.29 13.27 13.25 13.23
28 13.11 13.09 13.07 13.05 13.03
~J ., 29 12.90 12.88 12.86 12.84 12.82
30 12.71 12.69 12.67 12.65 12.63 ''-~-:-•
J
]
256
TABLE XI (continued)
Temp. 6.5 0.6 0.7 0.8 o.9
0 22.85 22.79 22.73 22.68 22.62
1 22.29 22.23 22.18 22.12 22.07
2 21.74 21.68 21.63 21.57 21.52
3 21.20 21.14 21.09 21.04 20.98
4 20.69 20.64 20.59 20.54 20.49
5 20.19 20.14 20.09 20.04 19.99
6 19.71 19.66 19.62 19.57 19.53
7 19.26 19.21 19.17 19.12 19.08
8 18.81 18.77 18.72 . 18.68 18.63
9 18.38 18.33 18.29 18.25 18.20
10 17.98 17.94 17.91 17.87 17.84
11 17.61 17.57 17.53 17.49 17.45
12 17.23 17.19 17.15 17.11 17.07
-----13 16.88 16.84 16.81 16.78 16.74
14 ·16.55 16.51 16.48 16.45 16.41 . 15 16.22 16.19 16.16 16.12 16.09
16 15.91 15.88 15.85 15.82 15.79
17 15.62 15.59 15.56 15.53 15.50
18 15.33 15.30 15.27 15.24 15.21
19 15.04 15.01 14.98 14.96 14.93
20 14.79 14.76 14.74 14.72 14.69
21 14.54 14.51 14.49 14.46 14.44
22 14.30 14.27 14.25 14.23 14.20
23 14.07 14.04 14.02 14.00 13.97
24 13.85 13.83 13.81 13.79 13.77
25 13.63 13.61 13.58 13.56 13.53
26 13.41 13.39 13.37 13.35 13.33
27 13.21 13.19 13.17 13.15 13.13
28 13.01 12,98 12.96 12.94 12.92
29 12.81 12.79 12.77 12.75 12.73
30 12.62 12.60 12.58 12.56 12.54
--la~
'\~
~ 1
.I
J
I
r 1
]
]
,-~
]
]
. j
1
J
J
t,:;,,,
U'
APPENDIX B
Methods of Gas Analysis
Oxygen in water. Dissolved oxygen content of water
was determined by the Winkler procedure as described in the
Standard Methods for the Examination of Water and Waste-
water. Water samples were drawn into 300.:!:. 0. 5 ml BOD
bottles. Two ml quantities of manganous sulfate, alkaline
iodide and sulfuric acid were used throughout to assure fix-
ation of oxygen at high gas tensions. A ZOO ml aliquot-was
titrated with 0. OZN sodium thiosulfate. The titration volume
was corrected for the 4 ml of water displaced by the first
two reagents by multiplying by the factor 1. 013. Thiosul-
fate solutions were standardized periodically and corrected to
within .:!:. 1 per cent.
Nitrogen in water. Water analysis for dissolved nitro-
gen was conducted by means of the apparatus of Scholander,
van Dam, Claff and Kanwisher ( 1955). The technique des-
cribed by these authors was altered somewhat to replace: the'
reagent alkaline pyrogallol with commercially available oxygen
absorber ( Oxorbent, Burrell Corp., Pittsburgh, Pa.). This
oxygen absorber was incompatible· with the alkaline citrate
normally used in the gas analyzer. Alternatively the analyzer
was filled with a saturated solution of sodium chloride as
258
described by Hoar ( 1960) for use in gas analysis. Water
nitrogen was calculated after the method of Scholander et al.
( 1955), correcting for nitrogen in the reagents by means of
blank determinations, for nitrogen remaining in the liquid phase
in the extractor and for water vapor pressure, temperature
and barometric pressure, thus reducing the gas volume to con-
ditions of standard temperature and pressure. The accuracy
of the dissolved nitrogen method was such that twenty analy-
ses on air-equilibrated, distilled water averaged 100.5 per cent
of air saturation, with· one standard deviation .:!: 2 o 1 per cent.
Dissolved nitrogen in fish blood. Dissolved nitrogen
was determined by a modification of the techniques of Edwards,
Scholander and Roughton ( 1943) and Sundes ( 1960) , utilizing
the extractor and gas analyzer of Scholander, van Dam, Claff
and Kanwisher ( 1955).
The reagents were prepared and utilized as follows:
Heparin solution: 10 mg per ml of sodium heparin
Occlusion fluid: saturated sodium chloride colored with
methyl red indicq~.tor and barely acidified
with concentrated hydrochloric acid
Caprylic alcohol: ( 2-octanol)
.,
Acid sulphate solution: 150 g anhydrous sodium sulphate
dissolved in 500 ml of distilled water
and acidified with 25 ml concentrated
sulp~uric acid
l
~ll'(~~
-'-:·~:fJP
l
J
]
]~
J
J
J
" J
J
J.: .....
:T~t.;
'-.;._;,~
~J
J
259
Ferricyanide solution: 62.5 g potassium ferricyanide,
30.0 g potassium bicarbonate, and 2. 5
g of saponin dissolved in 250 ml of
water
Potassium hydroxide solution: 100 g potassium hydroxide
dissolved in water to a volume of 500
ml
Oxygen absorber: Oxorbent
The acid sulphate and ferricyanide solutions are essen-
tially those of Sundes ( 1960) and the occlusion fluid that of
Hoar ( 1960) • The oxygen absorber was stored under oil in
a separatory funnel and delivered into the gas analyzer by
means of a short length of polyethylene tubing. The other
solutions were held in reagent bottles and permitted to equi-
librate with air. The blood, caprylic alcohol, saturated sod-
ium chloride, and ferricyanide were injected into the extractor
by means of 0. 5 or 1. 0 ml tuberculin syringes fitted with
no 16 needles and short lengths of polyethylene tubing, the
20 per cent potassium hydroxide was injected into the extrac-
tor with a 5 ml syringe similarly fitted.
The extractor and gas analyzer were cleaned with acid
permanganate or acid dichromate solution and rinsed thoroughly.
The extractor was next" flushed with 0. 5 ml of acid sulphate
solution by drawing that volume of solution into the analyzer
260
then turning it tip up and running the plunger up and down o
The acid sulphate was expelled and this step repeated, re-
moving any air. The plunger was pushed home leaving the
syringe extension filled with acid sulphate {approximately 0.1
ml).
The fish were stunned (but not killed) electrically and
a blood sample obtained by heart puncture o The blood was
drawn into a heparinized 1 ml syringe, care being taken to
avoid excessive negative pressure o The blood sample was
large enough to permit the transfer of 0 o 4 ml of blood and
.. still leave 0 o2 ml or more of blood in the syringe with the
small volume of heparin from the needle. If any free gas
appeared in the sample either from gas leaving solution in the
blood or from air contamination, the sample was discarded.
Following transfer of the blood sample to the extrac-
tor, a small quantity of caprylic alcohol was necessary to
reduce frothing. It was desirable to use the smallest amount
possible o This was gauged by injecting the caprylic alcohol
into the extractor to the point o f bore enlargement 1. 5 em
from the tip (a volume of approximately 0.015 ml) of .the
syringe extension.
The clotting problem was overcome by next injecting
0. 5 ml of occlusion fluid into the extractor after the capry-
lie alcohol. The tip of the extractor was closed with a
J
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261
rubber cap and the contents mixed by shaking for a half-
minute,. Promptness in the addition of the caprylic alcohol
and sodium chloride to the blood in the extractor appeared
to lessen further the tendency of the blood to form large
clots.
The cap was removed and 0.3 ml of ferricyanide
solution injected into the extractor. The cap was replaced
and the extractor contents again shaken for one-half minute.
The result was a gas phase (carbon dioxide, nitrogen and
oxygen) of 3. 5 ml overlying 0. 9 ml of liquid.
The carbon dioxide of the gas was reabsorbed by
injecting 3. 0 ml of 20 per cent potassium hydroxide into the
extractor. If the blood had broken up properly it settled
to the bottom of the liquid in fine particles, floating clots
indicated trapped gas bubbles and the sample was discarded.
The gas bubble was rolled back and forth once over the
potassium hydroxide then forced up into the syringe extension.
The gas bubble was transferred to the gas analyzer
which previously had been cleaned and filled with occlusion
fluid. The bubble was drawn through the capillary into the
analyzer barrel then slowly returned to the capillary. The
excess fluid was removed from the cup at the end of the
analyzer, the length of the total-gas column recorded and
the bubble returned to the barrel. Oxygen absorber was run
262
into the cup and drawn through the analyzer until the barrel
was filled (approximately 0.3 ml). The gas bubble was rolled
about in the absorber then slowly returned to the capillary.
The length of the gas column, the temperature of the gas
analyzer, and the barometric pressure were recorded o
The nitrogen content was corrected to a dry gas at
standard temperature and pressure and expressed as volumes
-per cent. The calculation were based on the original work
of Peters and Van Slyke ( 1932) and on the Scholander, Van
Dam, Claff, and Kanwisher ( 1955) description for water.
1. Blank determinations for nitrogen in the reagents
were averaged and the mean value subtracted from the
measured length of the sample nitrogen column. The average
of 10 blanks was 12.8 mm. Thus for fish no o 1 the nitrogen
column was:
34.3 -12.8 = 21.5 mm
2. The remaining gas column was corrected to a
blood sample size of 1. 0 ml by multiplying by the inverse of
the sample size:
21.5 X 1 • 0 = 53 • 7 5 m m G.4
3. The length of the gas column in mm was converted
to cu mm with a calibration correction factor for the gas
analyzer. In this case the value was very close to 0. 283 thus:
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263
4. The recorded barometric pressure was temper-
ature corrected from the table of values to be found in the
40th Edition of the Handbook of Chemistry and Physics. At
19°C and a barometric pressure of 767 mm Hg the corrected
value was:
767 -2.4 = 764.6 mm Hg
5. The temperature-corrected barometric pressure
was corrected to a dry gas by subtracting the water vapor
pressure at the temperature of the gas analyzer ( 19°C):
764.6 -16.5 = 748.1 mm Hg
6. The nitrogen volume as a dry gas was cor:eected
to the standard pressure of 760 mm Hg
15.21 X 748.1 = 14.97
760
cu mm
7. The nitrogen volume at standard pressure was
corrected to the standard temperature of ooc from the
temperature ( 19°C) of the
273 14.97 X 292 = 14.00
gas analyzer:
cu mm
8. A small correction was made for nitrogen remain-
ing in solution in the syringe analyzer. The nitrogen in
solution was a function of the partial pressure and solubility
of lthe gas. The partial pressure of the nitrogen in the gas
phase:
264
N2 vol.
C02 + N2 + 02 vol.
X 760
In the example at hand the nitrogen column in the gas anal-
yzer was:
34.3 x 0.283 = 9.71 cu mm
The total gas phase was approximately 3. 5 ml or 3500 cu mm.
Thus the partial pressure of the nitrogen in the gas phase:
9.7 1 x 760 = 2 1 mm Hg 3500 •
The solubility of nitrogen at 19°C from the absorption co-
efficient, Handbook of Chemistry and Physics, was 15.70 cu
· mm per ml of water. For a liquid phase of 0. 9 ml at a
partial pressure of 760 mm Hg:
15.70 x 0.9 = 14.13 cu mm
Correcting to the nitrogen partial pressure of 2 .1 mm Hg
(from above) the volume of nitrogen remaining in solution
was:
2.1 x 14.13 = 0.039 cu mm
760
Thus the nitrogen volume of 9.71 cu mm was increased by a
factor of:
9.71 X 0.039 = 1.004
9.71
Correcting the volume from step no. 7, the nitrogen volume
was:
14.00 x 1.004 = 14.06 cu mm
~1
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265
of dry gas at standard temperature and pressure for a blood
sample of 1. 0 ml, or 1. 41 volumes per cent.
9. Theoretical values were calculated from the table
of absorption coefficients, Handbook of Chemistry and
Physics.
NOTE: The absorption coefficient should not be confused
c I with the coefficient of solubility, the latter being calculated
to the temperature and pressure at which the gas is mea-
'l sured. A fuller explanation may be found in Glasstone (1946).
At the sample temperature of 11.6°C the solubility
of dry nitrogen reduced to STP was 18.01 ml per liter,
,r obtained by interpolation between values in the table of
absorption coefficients. The recorded barometric pressure
J was temperature corrected as above:
767 -2.4 = 764.6 mm Hg
This corrected pressure was reduced to conditions of a dry
gas by subtracting the water vapor pressure at the temper-
c 1 ature of the sample:
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764.6 -10.2 = 754.4 mm Hg
In the dry air the partial pressure of nitrogen (the
noble gases in the air were also considered as nitrogen here)
was:
0.7905 x 754.4 = 596.4 mm Hg
266
Correcting the absorption coefficient value to this
nitrogen partial pressure, at 11. 6°C the theoretical nitrogen
content of air-equilibrated water was:
18.01 x 596.4 = 14.14 ml per liter
760
or 1. 41 volumes per cent.
10. The percentage of air saturation was calculated
form the corrected experimental value, no. 8, and the
corrected theoretical nitrogen, no. 9:
14.06 x 100 = 99.4 per cent
14.14
11. Corrections were not made for certain lesser
inaccuracies. There was a difference in the size of the
liquid phase and hence a difference in the amount of nitrogen
remaining in solution in the blank and blood determinations.
The solubility of nitrogen in the reagents of the liquid phase
was less than that of the value for water used in the
calculation no. 8. This was opposed by the higher solubility
of nitrogen in blood than in water. A measure of this may
be found in Van Slyke, Dillon and Margaria ( 1934) •
Ten blank determinations averaged 12.8 mm with
one standard deviation + 0.4 mm. The average of 10 -.
determinations on distilled water, air-equilibrated in a ro-
tating flask was 101. a· .per cent of air saturation with
+ 2.1 per cent for one standard deviation. Ten blood
0
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267
determinations on rainbow trout held in a pond at 99 to 101
per cent of air saturation averaged 99.4 per cent with
.:!:. 2. 8 per cent for one standard deviation. The technique
described was employed successfully over the range of 100
to 135 per cent of air saturation (1.31 to 1.77volumes of
per cent).
A slightly more detailed description of this method
may be found in Harvey ( 1961).