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An experimental study of salinity preference and related migratory behaviour of juvenile Pacific salmon McInerney, John Edward 1961

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AN EXPERIMENTAL STUDY OP SALINITY PREFERENCE AND RELATED MIGRATORY BEHAVIOUR OF JUVENILE PACIFIC SALMON by JOHN EDWARD McINERNEY B.Sc, St. Patrick's Collage, University of Ottawa, 1959 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the DEPARTMENT OF ZOOLOGY We accept t h i s thesis as conforming to the standard required from candidates for the degree of MASTER OF SCIENCE Members of the Department of Zoology The University of B r i t i s h Columbia A p r i l , I961 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make I t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree that p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . The U n i v e r s i t y o f B r i t i s t r C o l u m b i a , Vancouver 8, Canada. Department o f Date // /9C A B S T R A C T The s e a s o n a l s a l i n i t y p r e f e r e n c e o f f o u r s p e c i e s o f P a c i f i c s a l m o n was e x a m i n e d . E a c h s p e c i e s showed a s t r o n g p r e f e r e n c e f o r h y p e r t o n i c s e a w a t e r d u r i n g t h e n o r m a l p e r i o d o f m i g r a t i o n . P i n k f r y ( O n c o r h y n c h u s g o r b u s c h a ) and coho y e a r l i n g s ( 0 . k i s u t c h ) l o s t t h i s p r e f e r e n c e d u r i n g t h e summer i n c o n t r a s t t o Chum f r y ( 0 . k e t a ) and s o c k e y e y e a r l i n g s ( 0 . n e r k a ) . T h r e e o t h e r t y p e s o f b e h a v i o u r showed s e a s o n a l c h a n g e s c o n s i s t e n t w i t h a t r a n s i t o r y " m i g r a t i o n d i s p o s i t i o n " . A p r e f e r e n c e f o r h y p e r t o n i c s e a w a t e r was a s s o c i a t e d w i t h h i g h l e v e l s o f a c t i v i t y , s t r o n g s c h o o l i n g t e n d e n c i e s and d e p r e s s e d a g g r e s s i v e b e h a v i o u r . S u b s e q u e n t s e a s o n a l c h a n g e s showed a marked i n c r e a s e i n a g g r e s s i v e b e h a v i o u r a c c o m p a n i e d b y d e c r e a s e d l e v e l s o f a c t i v i t y and g r o u p b e h a v i o u r . A l o n g d a i l y p h o t o p e r i o d (l6 h o u r s ) p r o l o n g e d t h e b e h a v i o u r c o m p l e x a s s o c i a t e d w i t h seaward m i g r a t i o n . A s h o r t d a i l y p h o t o p e r i o d (8 h o u r s ) d e l a y e d b u t d i d n o t t o t a l l y i n h i b i t t h e d e v e l o p m e n t o f a h y p e r t o n i c s a l i n i t y p r e f e r e n c e and a s s o c i a t e d b e h a v i o u r . The p r e f e r e n c e o f chum s a l m o n f r y f o r a s e r i e s o f s e a -w a t e r c o n c e n t r a t i o n i n d i c a t e d a n a l l - o r - n o n e t y p e r e s p o n s e . A c o n s i s t e n t l y s t r o n g p r e f e r e n c e was shown f o r s e a w a t e r h y p e r -t o n i c t o p l a s m a c h l o r i d e l e v e l s a s r e p o r t e d i n t h e l i t e r a t u r e . No p r e f e r e n c e was shown f o r h y p o t o n i c s e a w a t e r . A series of experiments i n which the composition of an a r t i f i c i a l seawater was altered indicated that under natural conditions the expression of a preference f o r s a l t water probably depends on the concentration of sodium chloride. The swiftness of the response (chum and sockeye) indicated stimu-l a t i o n of a peripheral s a l i n i t y receptor. Coho underyearlings injected with mammalian somatatropin showed an increased although not s t a t i s t i c a l l y s i g n i f i c a n t preference f o r hypertonic sea water. Both a c t i v i t y and aggress-ive behaviour were depressed i n comparison to control f i s h . i i i TABLE OP CONTENTS Page 1. INTRODUCTION 1 11. MATERIALS AND METHODS 3' Materials 3 Apparatus 3 Testing Procedure 6 Observations 8 Analysis of Data 9 Chemical Methods 11 111. RESULTS 12 A. Experimental Response Patterns 12 B. Seasonal Changes i n S a l i n i t y Preference 18 C. The E f f e c t s of Seawater Concentration on S a l i n i t y Preference 2ij. D. The E f f e c t s of Seawater Composition on S a l i n i t y Preference 2l+ E. Seasonal Changes i n Behaviour 3l+ P. The Behavioural E f f e c t s of Somatotropin Injection 1+2 IV. DISCUSSION if 6 A. Seasonal Behaviour Cycles l i° B. Endocrine Factors k-9 C. The Sensory Basis of S a l i n i t y Preference 3>1 D. The B i o l o g i c a l Significance of S a l i n i t y Preference £5 iv Page V. SUMMARY 59 • I . LITERATURE CITED 6l V I I . APPENDIX 61+ V LIST OP FIGURES Page Figure 1. Diagram of s a l i n i t y preference tank £ Figure 2 . Diagram of s a l i n i t y preference apparatus 7 Figure 3» S a l i n i t y preference experiment response patterns, chum f r y 13 Figure ii. S a l i n i t y preference experiment response patterns, sockeye yearlings • ll|. Figure $. Seasonal response patterns In control experiments, pink f r y 17 Figure 6. Seasonal s a l i n i t y preference, chum f r y 19 Figure 7» Seasonal s a l i n i t y preference, sockeye yearlings 20 Figure 8. Seasonal s a l i n i t y preference, pink f r y 22 Figure 9« Seasonal s a l i n i t y preference, y e a r l i n g coho exposed to various photoperiods 23 Figure 10. The eff e c t s of seawater concentration on s a l i n i t y preference • 25 Figure 11 . A comparison of the response to natural and a r t i f i c i a l seawater 27 Figure 12. A comparison of the response to standard a r t i f i c i a l seawater and a r t i f i c i a l seawater with the standard cation complement but chloride as the only anion 29 Figure 13* A comparison of the response to standard a r t i f i c i a l seawater and a r t i f i c i a l seawater with the standard anion complement but sodium as the only cation 30 v i Page F i g u r e 1I4.. A comparison o f t h e response t o standard a r t i f i c i a l seawater pH 7-9 a*10" a r t i f i c i a l seawater pH 6 .3 32 F i g u r e l£. A comparison o f the response t o standard a r t i f i c i a l seawater and o s m o t l c a l l y e q u i v a l e n t sucrose s o l u t i o n 33 F i g u r e 16. Seasonal behaviour changes, chum f r y 35 F i g u r e 17• A comparison of sea s o n a l behaviour changes i n v a r i o u s experimental treatments, chum f r y 37 F i g u r e 1 8 . Seasonal behaviour changes, sockeye y e a r l i n g s 38 F i g u r e 19. Seasonal behaviour changes, pink f r y 39 F i g u r e 2 0 . Seasonal behaviour changes, y e a r l i n g coho exposed to v a r i o u s photoperiods • i+1 F i g u r e 2 1 . The e f f e c t s o f somatotropin on s a l i n i t y p r e f e r e n c e , u n d e r y e a r l i n g coho .... 1+3 F i g u r e 2 2 . B e h a v i o u r a l e f f e c t s o f somatotropin ........ 1+5 v i i LIST OF TABLES Page T a b l e I . Data on experimental salmon stock s k T a b l e I I . Response o f chum f r y to a s e r i e s o f a r t i f i c i a l seawater c o n c e n t r a t i o n s • 26 Table I I I . Composition o f standard a r t i f i c i a l seawater 2? Table IV. Composition o f a r t i f i c i a l seawater with standard c a t i o n composition and c h l o r i d e as the o n l y anion 29 T a b l e V. Composition o f a r t i f i c i a l seawater wi t h standard a n i o n composition and sodium as the o n l y c a t i o n 30 T a b l e V I . Composition of standard a r t i f i c i a l seawater p.H. 6.3 • • 32 Table V I I . Composition o f standard a r t i f i c i a l seawater, s a l i n i t y 10.9 and an o s r a o t i c a l l y e q u i v a l e n t sucrose s o l u t i o n 33 T a b l e V I I I . Seasonal and experimental s a l i n i t y p r e f e r e n c e data, chum f r y 65 T a b l e IX. Seasonal behaviour data, Chum f r y 67 T a b l e X. Seasonal s a l i n i t y p r e f e r e n c e , sockeye y e a r l i n g s 68 T a b l e XI. Seasonal behaviour data sockeye y e a r l i n g s 69 T a b l e X I I . Seasonal s a l i n i t y p r e f e r e n c e , p i n k f r y 70 v i i i Page Table XIII. Seasonal behaviour data, pink f r y 71 Table XIV. Seasonal s a l i n i t y preference, ye a r l i n g coho exposed to various photoperiods 72 Table XV. Seasonal behaviour data, y e a r l i n g coho exposed to various photoperiods 73 ACKNOWLEDGEMENTS The author wishes t o s i n c e r e l y thank P r o f e s s o r W.S. Hoar F.R.C.S. f o r s u p e r v i s i n g and s u p p o r t i n g t h i s study a l s o P r o f e s s o r s C.C. L i n d s a y and R.N. Band f o r t h e i r advice and c r i t i c i s m . The author i s a l s o indebted t o Mr. T. Royal and Mr. H. Harvey bo t h o f the I n t e r n a t i o n a l P a c i f i c Salmon Com-m i s s i o n and Mr. S. Smith o f the B r i t i s h Columbia Commission f o r p r o v i d i n g the bulk o f the experimental s t o c k s . To h i s f e l l o w graduate students Mr. J . Wiggs and Mr. G. E a l e s the author extends h i s thanks f o r s t i m u l a t i n g d i s c u s s i o n and c o n s t r u c t i v e c r i t i c i s m . Support i n p a r t was p r o v i d e d by a F i s h e r i e s Research Board S c h o l a r s h i p . I. INTRODUCTION The seaward migration of juvenile P a c i f i c salmon i s characterized by far-reaching p h y s i o l o g i c a l and behavioural changes. Many of these anticipate actual entry into s a l t water and evidently preadapt the young salmon f o r a marine existence. Included i n t h i s group of changes Is the develop-ment of a preference f o r hypertonic seawater. S a l i n i t y preference can be^regarded as a discrete component of the behavioural repetoire of juvenile salmon. As such i t i s broadly dependent on two groups of causal factors - one external and the other i n t e r n a l (Tinbergen 1952). This d i v i s i o n provides a convenient basis f o r an experimental analysis of s a l i n i t y preference. E a r l i e r work has demonstrated the a b i l i t y of young salmon to detect s a l i n i t y differences (Houston, 1956, Baggerman, i960). The analysis of s a l i n i t y preference i n terms of external causal factors involves the i d e n t i f i c a t i o n of the seawater properites which provide the releasing s t i m u l i . Such an analysis would also permit an i n d i r e c t characterization of the complimentary sensory receptors. S a l i n i t y preference has also been shown to follow a season-a l pattern of development and regression (Baggerman, i960). This implies a change i n "motivation" since the f i s h respond d i f f e r e n t l y at various times, to the same releasing s i t u a t i o n . The analysis of s a l i n i t y preference i n terms of i n t e r n a l causal fac t o r s involves an analysis of the physiological mechanisms 2 responsible f o r changing l e v e l s of "motivation" or "drive". In t h i s regard the length of the d a i l y photoperiod has been shown to play an important r o l e i n the timing of these changes (Baggerman, i 9 6 0 ) . On t h e o r e t i c a l grounds the increas-ing d a i l y photoperiod associated with spring migration might be expected to act i n either of two ways. A d i r e c t action on c e n t r a l nervous system to modify "motivation" i s one p o s s i b i l i t y . Another more frequently proposed mechanism suggests that changing photoperiods act v i a the hypothalmus to stimulate endocrine secretion. This i n turn might modify motivation i n one of two ways: either by a d i r e c t hormone action on the central nervous system or i n d i r e c t l y by modifying some metabolic function. For example, i n t e r n a l sensory stimuli a r i s i n g from hormonally altered e l e c t r o l y t e l e v e l s could modify s a l i n i t y preference. This provides a b r i e f description of the framework within which the studies of t h i s thesis f a l l . The purpose of the study i s to evaluate the b i o l o g i c a l significance of s a l i n i t y preference as a c h a r a c t e r i s t i c behaviour of young salmon. I I . MATERIALS AND METHODS MATERIALS The four species of P a c i f i c salmon used i n the investiga-t i o n were chum (Oneorhynchus keta), pink ((). gorbuscha), sockeye ( 0 . nerka) and coho ( 0 . kisutch). Each species was maintained separately In running, dechlorinated water at the University of B r i t i s h Columbia. Seasonally the temperature ranged from a winter low of ii°C. to a l a t e summer high of 1 1 L ° C Two groups of y e a r l i n g coho were maintained i n l i g h t proof boxes; one with an eight hour d a i l y photoperiod, the other with sixteen hours. Both photoperiods were begun on December 17* 19^9 and] continued through September of i 9 6 0 . A l l other f i s h were exposed to natural day lengths. Occasionally night work near holding tanks resulted i n i r r e g u l a r but short periods of a r t i f i c i a l i l lumina-t i o n . Experimental stocks were fed "Clarks f i s h food" three times d a i l y during the period of i n v e s t i g a t i o n . Data on hatchery, holding conditions, seasonal size of f i s h , o r i g i n a l source of stocks and date of a r r i v a l at the u n i v e r s i t y hatchery are recorded In Table I. APPARATUS The method used i n t e s t i n g s a l i n i t y preference has been described by Houston (19^6) and Baggerman (1957. »59> ' ° 0 ) . B a s i c a l l y i t permits the f i s h to choose between two connected compartments - one containing salt and the other fresh water (PIG. 1 ) . In the present series of experiments six such TABLE I DATA ON EXPERIMENTAL SALMON STOCKS Species Year Class Hatchery Conditions Mean Fork Length Centimeters Date Measured Source Date of A r r i v a l at University Hatchery Early Summer Late Summer Chum Under-yearling Normal 3.70 June 8, J. i960 8.53 Sept. 7, i960 Smith F a l l s Hatchery, Cultus Lake, B. C. May 6, i960 Pink Under-yea r l i n g Normal 3.28 June 8, i960 945 Sept. 7, i960 Smith F a l l s Hatchery, Cultus Lake, B.C. May 6, i960 Sockeye Yearling Normal 8.6k June 0, i960 13.11+ Sept. 7, i960 Downstream migrants Cultus Lake Outlet Cultus Lake, B.C. May 6, i960 Coho Yearling Normal 8.95 May 30, i960 Salmon River Langley Area, B.C. Nov. 10, 1959 And Dec. 17, 1959 l6 hour dai l y photo-period 9-10 May 30, i960 IO.99 Sept. 7, i960 8 hour daily photo-period 9.93 May 30, i960 ll.Oif Sept. 7, i960 Under-yearling Normal 6.30 Sept. 25, i960 1st week of August, i960 © FRESH WATER COMPARTMENT © SALT WATER COMPARTMENT ® PARTITION SEPARATING I&2 @ SHALLOW "BRIDGE" OF WATER CONNECTING I&2 © COMBINATION FILLING & DRAINING ORIFICES © AIR SUPPLY (7) WATER LEVEL F I G U R E I . D I A G R A M O F S A L I N I T Y P R E F E R E N C E T A N K 6 divided tanks were used. The physical arrangement i s i l l u s -trated In Pi g . 2. The temperature of the experimental solution was main-tained approximately equal ( 1°C) to that of the hatchery holding tanks by means of a continuous flow water bath. Lighting was provided by Westinghouse 60 watt "Lumiline" incandescent bulbs from an overhead p o s i t i o n . Most of the l i g h t f a l l i n g on the tanks was by way of r e f l e c t i o n from Inclined mirrors (Pig. 2). The l i g h t i n t e n s i t y was maintained at l.J|6- 0.17 foot candles measured at the water surface. TESTING PROCEDURE Two types of experiments were conducted on a paired basis. In the control experiment both compartments of the p a r t i c u l a r tank being used were f i l l e d with f r e s h water. In the s a l i n i t y experiment one compartment was f i l l e d with fresh water and the other with s a l t water. I n i t i a l l y each oompart-ment was f i l l e d only to the l e v e l of the separating p a r t i t i o n so that no exchange between compartments was possible. Eight f i s h were then placed i n one compartment of each tank; always Into fresh water i n the s a l i n i t y experiment. They were allowed to remain undisturbed for a period of 3a to l | i hours. Fresh water was then added to the compartment i n which the f i s h were o r i g i n a l l y placed. The rate of flow, through a bottom center i n l e t , was adjusted to avoid strong currents. Water was added u n t i l a "bridge" 2.5 centimeters deep at the p a r t i t i o n , connected the two adjacent compartments © 'NQi , C O A / 54 8 thus permitting the f i s h to move fr e e l y between them. The compartment into which the f i s h were o r i g i n a l l y placed was for convenience l a b e l l e d the " o r i g i n a l compartment" and the connect-ing one the "test compartment". Some s l i g h t exchange of s a l t and fresh water took place i n the s a l i n i t y experiments. However the basic assumption of a steep s a l i n i t y gradient was maintained throughout the duration of each experiment. A c r i t i c a l examination of t h i s aspect of the method has been performed by Houston (1956,57)• Aeration was supplied to each compartment only during the period of adaptation. Slight differences i n oxygen content between fresh and s a l t water compartments were assumed not to affec t the behaviour of the f i s h (Houston, 1956).-OBSERVATIONS Once the bridge was established observations were begun. The d i s t r i b u t i o n of f i s h i n each tank was recorded f i v e times i n each ten minute period of observation. Periods were begun at 0, 15, i+5, 75, 105, 135, 165 and 195 minutes. Records of a c t i v i t y , group behaviour and agonistic behaviour i n i n d i v i d u a l tanks were made continuously f o r f i v e minute periods i n the int e r v a l s between observations on d i s t r i b u t i o n . A l l experiments were carr i e d out between one and s i x f.M. Observations were made by looking through slotted panels of curtains from a darkened background into mirrors suspended over the experimental tanks. In t h i s way the f i s h appeared unaffected by the observers presence. 9 ANALYSIS OF DATA (i ) S a l i n i t y preference data The f i v e d i s t r i b u t i o n values recorded during each period of observation f o r each control experiment were averaged. The averages for a l l the r e p l i c a t i o n s of a given experimental period were summed. Chi-square analysis ("2 by N" test) was used to determine the si g n i f i c a n c e of the departure of these summed averages from a uniform d i s t r i b u t i o n . A statement of sig n i f i c a n c e for the control experiment as a whole was obtained by taking a grand mean of the eight observation periods for a l l r e p l i c a t i o n s . This again was tested against a uniform d i s t r i -bution (Snedecor, 1956). D i s t r i b u t i o n s i n the s a l i n i t y experiments, otherwise treated i d e n t i c a l l y , were s t a t i s t i c a l l y compared with the control experiment. In the appendix (Tables VIII, X, XII, XIV) chi-square values having a p o s i t i v e s i g n indicate a d i s t r i b u t i o n favouring the test compartment. A negative sign indicates a d i s t r i b u t i o n favouring the o r i g i n a l compartment. A l l chi-squares are associated with one degree of freedom. Values of 3 •8li r and 6.63 indicate departures s i g n i f i c a n t at the $% and 1% l e v e l s respectively. ( i i ) A c t i v i t y , group behaviour and aggressive behaviour. The number of i n d i v i d u a l s that crossed the tank p a r t i t i o n during continuous f i v e minute periods of observation was taken as a measure of general a c t i v i t y . (l)The calculated values are "pooled chi-squares" (Snedecor,1956) 10 Active schooling behaviour was measured by noting the size of each group which crossed the tank p a r t i t i o n . An average group size was calculated f o r each period of observation. Schools consisted of two or more f i s h showing a close and con-stant s p a t i a l r e l a t i o n s h i p while crossing the tank p a r t i t i o n i n the same d i r e c t i o n (Keenleyside, 1955)* Separate assessments of aggressive behaviour were made by noting the number of times "nipping" and "chasing" occured during f i v e minutes observation. (Stringer and Hoar, 1955) In nipping the aggressor made a quick darting movement toward another f i s h . Usually the motion was directed towards the l a t e r a l caudal peduncle or posterior flank region, less f r e -quently towards the opercular region. In many cases the attack stopped short of bodily contact. When contact occurred It ranged from a simple nudging motion to actual b i t i n g . Frequently the intended v i c t i m attempted to avoid the attack by f l e e i n g . I f pursuit by the attacker resulted t h i s was recorded as chasing. Each value shown for a l l types of data i s the mean of a number of r e p l i c a t i o n s . The actual number i s recorded with the appropriate table i n the appendix. ( i i i ) Unknown variables Many factors might affect both d i s t r i b u t i o n and behaviour observations. V i s u a l cues i n the apparatus may have permitted the f i s h to orient to objects other than the test solutions. Small differences i n l i g h t i n t e n s i t y along with shadowing produced by the arrangement of mirrors might have affected both types of observations. Accordingly the compartments and tanks 11 used f o r p a r t i c u l a r treatments were chosed randomly from twenty-four combinations. Depending on the available stock of a p a r t i c u l a r species an e f f o r t was also made to avoid repeating the same group of f i s h on consecutive days. CHEMICAL METHODS A r t i f i c i a l sea water solutions were made from reagent grade chemicals and dechlorinated tap water according to the composition tables of Barnes (1951+) • C h l o r i n i t y determinations were made by the Mohr t i t r a t i o n of t o t a l chlorides. S a l i n i t y adjustments of natural sea water were made with dechlorinated (2) tap water and commercial coarse s a l t ; A "Photovolt" model 85 pH meter with standard electrodes was found satisfactory for pH determinations. (2) Evaporated San Francisco Bay Sea Water, sa l t k i l n dried and half-ground. Vancouver Salt Co., Vancouver, B.C. 12 I I I . RESULTS A. Experimental response patterns Two of the species studied, chum and sockeye, showed a consistent seasonal preference for hypertonic seawater. (Pig. 6 and 7 ) . The data of eight seasonal tests (92 r e p l i -cations) for chum and three seasonal t e s t s (36 r e p l i c a t i o n s ) for sockeye have been combined i n analyzing the experimental response patterns. Figures 3 and II show a comparison of the test compartment d i s t r i b u t i o n s i n s a l i n i t y and control experiments. Graphically t h i s provides the most direct index of s a l t water preference since the experimental design was such that s a l i n i t y and control experiments d i f f e r e d i n one respect only — the type of water i n the respective test compartments. Each curve shows one major i n f l e c t i o n . The steep slope before the i n f l e c t i o n Indicates an i n i t i a l s h i f t i n d i s t r i b u t i o n from the o r i g i n a l to the test compartment. Following the i n f l e c t i o n the d i s t r i b u t i o n became more or less s t a b i l i z e d . In the control experiments, chum f r y showed a more rapid d i s t r i b u t i o n s h i f t from the o r i g i n a l to the test compartment than sockeye. The majority of both species always occupied the o r i g i n a l compartment. Patterns of response i n s a l i n i t y experiments are similar for both species. Except f o r the f i r s t period of observation the majority of f i s h always occupied the sea water compartment. i 3 F i g u r e J>. S a l i n i t y p r e f e r e n c e response • p a t t e r n s , chum f r y ; extremes o f seasonal v a r i a t i o n r e p resented by v e r t i c a l b a r s Ik F i g u r e k- S a l i n i t y p r e f e r e n c e response p a t t e r n s , sockeye y e a r l i n g s ; extremes of seasonal v a r i a t i o n r e p r e s e n t e d by v e r t i c a l b a r s . T I 1 1 1 1 — i r 1 5 Even i n the f i r s t observation period more f i s h occupied the test compartment of the s a l i n i t y experiment than the corres-ponding control experiment compartment, in d i c a t i n g a preference for salt water. Three features of the response patterns bear on the present study. Ten or twelve paired experiments were performed each time a species seasonal preference was tested. The range of v a r i a b i l i t y for seasonal tests i s indicated by v e r t i c a l bars i n Pig. 3 and I+. No attempt was made to analyze the sources of this v a r i a b i l i t y but some general comments are possible. To determine whether more f i s h were found i n one compart-ment or another repeated instantaneous counts were made f i v e times i n each ten minute,period of observation. The method I t s e l f introduces a source of v a r i a b i l i t y since the d i s t r i -butions were dynamic rather than s t a t i c . Chum f r y crossed the tank p a r t i t i o n as many as thirteen times per minute. The method had the advantage of permitting six simultaneous r e p l i c a t i o n s . An additional source of v a r i a b i l i t y might be expected from differences In the response i n the s i x tanks used f o r the study. The random choice of tanks and compartments did not eliminate t h i s source but distributed i t i n such a way that p a r t i c u l a r treatments were not biased. A second feature of the response was the r a p i d i t y with which s t a t i s t i c a l l y s i g n i f i c a n t differences i n d i s t r i b u t i o n were established between control and s a l i n i t y experiments. 16 With sockeye t h i s consistently occurred i n the f i r s t ten minutes. With chum s i g n i f i c a n t differences were frequently found i n the f i r s t ten minutes and always within the i n i t i a l 55 minutes. The t h i r d feature, already mentioned, was that i n control experiments the majority of f i s h almost always occupied the o r i g i n a l compartment. This was true of a l l species. Pink f r y were unique In showing a s t a t i s t i c a l l y s i g n i f i c a n t seasonal change i n " o r i g i n a l compartment preference". Figure 5 shows the control response patterns i n June and August are s i m i l a r . By contrast the September response shows that consistently fewer f i s h occupied the test compartment (more f i s h occupied the o r i g i n a l compartment. Houston (1956) suggested two possible explanations, one involving v i s u a l and the other o l f a c t o r y cues. Hoar (1958) has shown that juvenile salmon can apprehend and r e t a i n s p a t i a l r e l a t i o n s h i p s . Many v i s u a l cues existed i n the apparatus which might e a s i l y have permitted the f i s h to i d e n t i f y the o r i g i n a l compartment. Odours produced i n the o r i g i n a l compart-ment during the period of adaptation {3ik to hfe hours) provide another possible cue. Baggerman (i960) used short adaptation periods ( 20 min-utes). A s u p e r f i c i a l comparison of the effects of long (Houston, 1956) and short periods of adaptation suggests that longer periods produce a more consistent " o r i g i n a l compartment preference". Apparently some learning of either v i s u a l or o l f a c t o r y cues or both accounts f o r the " o r i g i n a l compartment 17 Figure Seasonal response patterns i n contro l experiments, pink f r y . 70 i I • AUGUST • JUNE O SEPTEMBER z 6 0 _L • rr l < • Sh. J_CO X O 5 20 50 80 UO M IN U T ES 140 170 20QM EAN 18 preference" c h a r a c t e r i s t i c of control experiments. B. Seasonal changes i n s a l i n i t y preference Seasonal changes i n s a l i n i t y preference were analyzed by comparing the mean experimental responses. Each test was made with natural seawater adjusted to 25 (±l%o) s a l i n i t y except as noted for chum f r y . 1. Chum f r y Seasonally chum f r y showed a consistent preference f o r hypertonic seawater. Figure 6 (Table VIII) shows that an average of 19*6$ more f i s h occupied the test compartment of the s a l i n i t y experiment than the corresponding control compartment. Seasonal va r i a t i o n s (—6%) showed no consistent trends. A l l but two experiments were made with an a r t i f i c i a l nine component seawater, 27.1 11 %o s a l i n i t y (Barnes, 195^) • The f i r s t experiment (May) was made with natural seawater 25*HXsalin-i t y . The next seasonal test (June) shows two points,one natural seawater and the other standard a r t i f i c i a l seawater. The response to the two solutions was not s t a t i s t i c a l l y d i f f e r e n t . ( F i g . 11) 2 . Sockeye yearlings Figure 7 (Table X) shows that sockeye preferred hyper-tonic seawater i n June, July and August. Later t e s t i n g would probably have shows a loss of t h i s preference (Baggerman, i 9 6 0 ) . The d i s t r i b u t i o n differences between s a l i n i t y and control experiments was si m i l a r to chum ( 1 9 . 8 $ ) . Sockeye showed a stronger tendency than chum to remain i n the o r i g i n a l compart-ment. 19 F i g u r e 6. Seasonal s a l i n i t y p r e f e r e n c e , Chum f r y ; v e r t i c a l b a r equals d i s t r i b u t i o n d i f f e r e n c e s t a t i s t i c a l l y s i g n i f i c a n t a t l e v e l . CHUM FRY r T T L U eo\ r -o u r -L U h-40 to LL >S 2Qr MAY J U N E | JULY O CONTROL EXP. • SALINITY EXP AUGUST | SEPTEMBER 20 Figure 7*./ Seasonal salinity preference^ ; sockeye yearlings; vertical bar equals distribution difference st a t i s t i c a l l y significant at 5% -level SOCKEYE YEARLINGS z60f u i H r -LU | 2 o , O CONTROL EXP • SALINITY EXP AUGUST | SEPTEMBER MAY JUNE J ULY 21 3. P i n k f r y F i g u r e 8 ( T a b l e X I I ) shows t h a t p i n k f r y p r e f e r r e d h y p e r t o n i c s e a w a t e r i n l a t e J u n e b u t n o t i n A u g u s t and September. As m e n t i o n e d e a r l i e r t h e t e n d e n c y t o r e m a i n i n t h e o r i g i n a l compartment shows a n a p p a r e n t s e a s o n a l change b e t w e e n A u g u s t and S e p t e m b e r . 1L. Coho y e a r l i n g s T h r e e g r o u p s o f ooho y e a r l i n g s were ex a m i n e d . One group was e x p o s e d t o n o r m a l d a i l y p h o t o p e r i o d s ( c o n t r o l ) , t h e s e c o n d t o an e i g h t h o u r d a i l y p h o t o p e r i o d and t h e t h i r d t o s i x t e e n h o u r s . The c o n t r o l and e i g h t h o u r g r o u p s w e r e e a c h t e s t e d o n c e . T h e s i x t e e n h o u r g r o u p was t e s t e d o n t h r e e o c c a s i o n s . F i g u r e 9(Table X I V ) shows t h a t t h e c o n t r o l g r o u p d i d n o t p r e f e r h y p e r t o n i c s e a w a t e r i n e a r l y J u n e . E x a m i n a t i o n o f Baggerman's (i960) d a t a s u g g e s t s t h a t by Ju n e y e a r l i n g coho e x p o s e d t o n o r m a l day l e n g t h s would b e e x p e c t e d t o ha v e l o s t t h e i r h y p e r t o n i c s a l i n i t y p r e f e r e n c e . F i s h e x p o s e d t o a s i x t e e n h o u r d a i l y p h o t o p e r i o d showed no p r e f e r e n c e f o r h y p e r t o n i c s e a w a t e r i n l a t e May, a s t r o n g p r e f e r e n c e i n J u l y and no p r e f e r e n c e I n A u g u s t . The J u l y r e s u l t s p r o b a b l y r e p r e s e n t s t h e d e v e l o p m e n t o f a s e c o n d p e r i o d o f s e a w a t e r p r e f e r e n c e and c o n f i r m s Baggerman's (i960) o b s e r -v a t i o n s . The e i g h t h o u r g r o u p when t e s t e d i n l a t e J u l y p r e f e r r e d h y p e r t o n i c s e a w a t e r . Baggerman (i960) c o n c l u d e d t h a t a n e i g h t h o u r p h o t o p e r i o d " p o s t p o n e s o r e v e n i n h i b i t s " t h e s e a s o n a l c h a n g e I n s a l i n i t y p r e f e r e n c e . The p r e s e n t r e s u l t s show t h a t 22 Figure 8. Seasonal s a l i n i t y preference, pink f r y ; v e r t i c a l bar equals d i s -t r i b u t i o n di f ference s t a t i s t i c a l l y s i g n i f i c a n t at 5% l e v e l . PINK FRY 2 60 r h-< CL 1 O <J40r H co UJ iL"20r ^ o O C O N T R O L E X P • S A L I N I T Y E X P M A Y J U N E I J U L Y I A U G U S T TsE P T E M B E R 23 F i g u r e 9» Seasonal s a l i n i t y p r e f e r e n c e , y e a r l i n g coho exposed to v a r i o u s photoperiods; v e r t i c a l bar equals d i s t r i b u t i o n d i f f e r e n c e s t a t i s t i c a l l y s i g n i f i c a n t at l e v e l . C O H O Y E A R L I N G S Z 6 0 R UJ h-< CL § 4 0 I -UJ I I if) LZ 2 0 • N O R M A L P H O T O P E R I O D O 1 6 - H O U R P H O T O P E R I O D ^ 8 - H O U R P H O T O P E R I O D S O L I D S Y M B O L S - S A L I N I T Y E X P H O L L O W S Y M B O L S - C O N T R O L E X P M A Y | J U N E | J U L Y | A U G U S T | S E P T E M B E R 2k the change i s delayed but not in h i b i t e d e n t i r e l y . C. The E f f e c t s of Seawater Concentration on S a l i n i t y  Preference The response of chum salmon f r y to six concentrations of the standard a r t i f i c i a l seawater was examined. The data f a l l into two groups (Pig. 10, Table I I ) . (I) The response to c h l o r i n l t i e s of 2 and i i % 0 d i d not d i f f e r s i g n i f i c a n t l y from the c o n t r o l response Indicating no preference, ( i i ) The response to c h l o r i n l t i e s of 5*6,10 and 15 /^indicated a strong preference f o r the test solutions. Further s t a t i s t i c a l tests showed the response w i t h i n each group to be homogeneous. The r e s u l t s show a sharp I n f l e c t i o n In response between I4. % 0and 5%a c h l o r i n i t y . In addition the responses before and aft e r the i n f l e c t i o n neither increase nor decrease w i t h i n the range examined. Kubo (1955) examined plasma chloride l e v e l s * n Qpcorhynohus masou. The average values f o r pre-migratory and migratory smolts (Figure 10) show a close r e l a t i o n to the i n f l e c t i o n i n preference. This suggests that s a l i n i t y prefer-ence hinges on plasma e l e c t r o l y t e concentration. A further examination of t h i s point w i l l be reserved for the discussion. D. The E f f e c t s of Seawater Composition on S a l i n i t y  Preferences The response of chum salmon f r y to major al t e r a t i o n s i n the composition of seawater was examined. 1. Comparison of natural and a r t i f i c i a l seawater Figure 11 (Table VIII) shows that the responses to natural seawater (25.^  %©salinity) and an a r t i f i c i a l nine 25 Figure 10. The Effects of seawater concentration on s a l i n i t y preference; refer to text f o r explanation of chi-square values. °/o FISH TEST COMPARTMENT CSALINITY EXP MINUS O CONTROL EXPD J O O r TABLE II Response of chum fry to a series of a r t i f i c i a l seawater concentrations 0/ Chlorinity /oo 2 k 5 6 10 15 Salinity %> 3.6 7.3 9.1 10.9 18.1 27.1 Control experi-ment $ Pish test.comp. 3l+.0$ lf6.7$ 30.9$ 36.2$ 30.9$ 3k.. 0$ Chi-square -9.76 -043 -13.95 -7.37 -13.95 -9.76 Salinity experi-ment $ Pish test. comp. 38.6$ 1+7.0$ 56.5$ 6l.2$ 59.9$ 56.5$ Chi-square 0.86 0.001+ 29.28 26.00 37.61+ 2145 Date ' Aug.8-13 Aug.29-Sept.3 Sept.5-10 July 29-Aug.3 Sept.5-10 Aug.8-13 $ Pish i n test comp-artment of salinity experiment minus $ f i s h i n test compT artment of control 1 experiment 1L. 6$ 0.3$ 25.6$ 25.0$ 29.0$ 22.5$ 2 7 Figure 11. Comparison of the response to natura l and a r t i f i c i a l seawater Table I I I . Composition of standard a r t i f i c i a l seawater, 21 »\%o s a l i n i t y , pH 7.9 MINUTES SALTS G R A M S / 1 5 LITERS SOLUTION NA C L 282.86 K CL 8.75 CA CLa 1 3.38 MG CL* C6H xO) 1 28.43 NA^SO* 47.30 NA H C 0 3 2.33 NA BR 1 .Ol SR CLa. Q6HzO^ 0.2I H 3 B O 3 0.32 28 component seawater (Table III) were s i m i l a r . Except for the f i r s t observation period no s i g n i f i c a n t difference was found between the response patterns. The experiment demonstrates that the minor components of natural seawater are of no Impor-tance i n the s a l i n i t y preference response. In the experiments to follow the s a l t solutions used were a l l modifications of the standard a r t i f i c i a l seawater (pH 7*8 i O . l ) . Except f o r the soluti o n used i n the suorose experiment a l l concentrations were equivalent to 27«1 ± 1 %>° s a l i n i t y . 2. Comparison of standard a r t i f i c i a l seawater and sea-water with chloride as the only anion (Table IV) Figure 12 (Table VIII shows the responses to both solu-tions were equivalent. No s i g n i f i c a n t difference was demon-strable either i n the pattern or mean response. Elimination of a l l but the p r i n c i p a l anion (chloride) of natural seawater does not a f f e c t s a l i n i t y preference. 3• Comparison of standard a r t i f i c i a l seawater and  seawAter with sodium as the only cation (Table V) Although the response patterns to the two seawaters showed some differences the mean responses were not s i g n i f i c a n t l y d i f f e r e n t ( F i g . 13, Table VIII). Elimination of a l l but the major cation (sodium) of natural seawater does not a f f e c t s a l i n i t y preference. The reasons f o r the d i f f e r e n t response patterns are not c l e a r . Examination of the composite behaviour graphs (Fig. 17, June 29-July $) shows that the l e v e l s of a c t i v i t y , schooling 29 Figure 12. A comparison of the response to standard a r t i f i c i a l seawater and a r t i f i c i a l seawater with the standard cation complement but chloride as the only anion. Table IV. Composition of a r t i f i c i a l seawater with standard cation composition and chloride as the only anion, s a l i n i t y equivalence 27.1%o pH adjusted to 7.9 with NaOH. D EXPERIMENTAL SEAWATER • ARTIFICIAL SEAWATER O CONTROL J I I L • 5 2 0 50 80 no 140 MINUTES 170 2 0 0 MEAN SALTS GRAMS/15 LITERS SOLUTION NA CL 3 2 4 . O l K CL 8.75 CACL* 1 3 . 3 8 MG CL Z C6HaO) I 2 8 . 4 3 SR CL* C6H.OO. Q 2 I 30 F i g u r e 13« A comparison of the response to standard a r t i f i c i a l seawater and a r t i f i c i a l seawater w i t h the standard a n i o n complement but solium as the o n l y c a t i o n . Table V. Composition of a r t i f i c i a l seawater with standard anion c o m p o s i t i o n and sodium a s the only c a t i o n , s a l i n i t y 21.1%0, pH 7 * 9 no MINUTES MEAN SALTS GRAMS/15 LITERS SOLUTION NA CL NA*S04 NA HC0 3 NA BR H,BOj 377.70 47.30 2.33 I .Ol 0.32 31 behaviour and aggressive behaviour were si m i l a r i n both experiments. i i . Comparison of the response to standard a r t i f i o i a l  seawater of pH 7.0" and b . 3 (Table VI) The c o n t r o l experiment was omitted i n t h i s comparison. I t may be i n f e r r e d from the seasonal graph (Pig. 6; July 21-21L) that chum f r y preferred hypertonic seawater at t h i s time. Figure li}. (Table VIII) shows that pH had no demonstrable eff e c t on the response. Both the patterns and mean response' were s t a t i s t i c a l l y equivalent. 5 . Comparison of standard a r t i f i c i a l seawater and osmotically equivalent sucrose solution. (Table VII) Figure 15 (Table VIII) i l l u s t r a t e s the strong preference shown f o r the standard seawater (10.9 %° s a l i n i t y ) . By contrast the response to the osmotically equivalent sucrose was strongly negative. Except for the f i n a l period of observation fewer f i s h were observed i n the test compartment of the sucrose experiment than i n the control experiment. The s i g n i f i c a n c e of t h i s experiment depends on the premise that the sweet taste did not contribute substantially to the negative response. Examination of the composite behaviour graph for chum f r y (Fig. 17) shows that the o v e r a l l a c t i v i t y i s only s l i g h t l y l e s s than i n the c o n t r o l and seawater experiments. Since a c t i v i t y was measured by counting the number of exchanges between compartments t h i s indicates that the f i s h repeatedly entered the sucrose s o l u t i o n . On the basis of t h i s i n d i r e c t evidence i t seems u n l i k e l y that the sweet taste contributed 32 F i g u r e A comparison of the response to standard a r t i f i c i a l seawater, pH 7«9 a*10" 6.3 T a b l e V I . Composition of standard a r t i f i c i a l , s a l i n i t y 27.1%o pH adjusted t o 6.3 hy omission o f sodium bicarbonate and a d d i t i o n o f HCl. • EXPERIMENTAL SEAWATER • ARTIFICIAL SEAWATER j i i 5 20 50 80 no MINUTES 140 170 200 MEAN SALTS GRAMS/B LITERS SOLUTION NA CL 282.86 K CL 8.75 CA CL* 1 3.38 MG CLAC6H^OD 128.43 NAaS04- 47.30 NA BR 1.0 1 SR CLa,C6H*.0) 0.2I H 3B0 3 0.32 33 Figure l5» A comparison of the response to standard a r t i f i c i a l seawater and osmotically equivalent sucrose solution Table VII. Composition of standard a r t i f i c i a l seawater, salinity 1 0 * 9 % o , p H 7»9 and osmotically equivalent sucrose solution. 1 I 1 1 1 1 r Z 6 0 LU r-£ § 4 0 CO LLl X LO LZ 2 0 • ARTIFICIAL SEAWATER O C O N T R O L • S U C R O S E I I L o • 5 2 0 50 80 M IIO INUTES 140 170 2 0 0 MEAN S A L T S G R A M s / l 5 LITER SOLUT ION NA C L 1 1 1.92 K C L 3.46 CA C L X 5.30 MG C L a C 6 H » 0 ) 5 0 . 8 2 N A * S 0 4 1 8.72 NA H C O j 0 .92 NA BR 0 4 0 S R C L n C e H ^ O ^ O.08 H 3 B O , O-1 3 S U C R O S E I 507 .95 3k substantially to the negative response. Within t h i s l i m i t a -t i o n the re s u l t s of the sucrose experiment indicate that chum fry i n showing a preference for hypertonic seawater do not respond to density or t o n i c i t y per se but more s p e c i f i c a l l y to the concentration of s a l t s . The combined r e s u l t s of t h i s section show that a prefer-ence for hypertonic seawater i s not dependent on the presence of s p e c i f i c minor components of natural seawater. The p o s i t i v e response observed when a l l but the major ions (sodium and chloride) were separately eliminated suggests that sodium chloride alone probably provides an adequate stimulus* The fact that t h i s salt i s the major constituent of both plasma and natural seawater favours the idea that the expression of a s a l t water preference under natural circumstances probably depends p r i n c i p a l l y on the concentration of sodium chloride. The r e s u l t s do not Indicate the extent to which other s a l t s may replace sodium chloride. E. Seasonal Behaviour Changes Three aspects of behaviour were examined on a quanti-ta t i v e seasonal b a s i s . Included were the l e v e l s of general a c t i v i t y , group behaviour and aggressive behaviour. 1. Chum f r y Figure l6 (Table IX) i l l u s t r a t e s the mid-summer peaks of a c t i v i t y and group behaviour shown by chum f r y . Declining l e v e l s of a c t i v i t y and schooling tendencies were accompanied by increased nipping. Seasonally, a c t i v i t y and group behaviour 35 Figure l 6 . Seasonal behaviour changes, chum fry; schooling behaviour - average size of groups crossing tank p a r t i t i o n a c t i v i t y - average number of i n d i v i d u a l p a r t i t i o n crossings per f i v e minutes observation aggressive behaviour - average number of nips per f i v e minutes observation C H U M F R Y 36 were inversely related to aggressive behaviour. The numerical values for schooling behaviour represent an experimental s i t u a t i o n that tended to disrupt any prolonged existence of active groups. The values should be interpreted as a measure of the r e a l tendency to form active aggregates rather than the performance that might be expected from a group of eight f i s h i n more natural surroundings. Figure 17 shows the s l i g h t differences i n behaviour between the various types of experiments. A similar order of differences, between s a l i n i t y and control experiments, was observed for the other three species. 2. Sockeye yearlings Figure 18 (Table XI) shows the seasonal behaviour data for sockeye. Only the l a t e seasonal changes were observed. Group behaviour showed a decline comparable to that observed f o r pink and coho. A c t i v i t y showed an i n i t i a l decline but then increased. Part of t h i s l a t e season Increase (27.6$) was d i r e c t l y a t t r i b u t a b l e to the accompanying increase i n aggressive behaviour. As such, the trend represents an experi-mental a r t i f a c t rather than a r e a l seasonal change i n a c t i v i t y . 3« Pink Fry Figure 19 (Table XIII) shows a seasonal decline i n group behaviour and a c t i v i t y . Once again only the l a t e seasonal trends were observed. In common with the other species Increasing aggressive behaviour accompanied de c l i n i n g l e v e l s of a c t i v i t y and schooling behaviour. 37 F i g u r e 17. A comparison o f seasonal behaviour changes i n v a r i o u s experimental treatments, chum f r y ; r e f e r to F i g . l 6 f o r e x p l a n a t i o n of behaviour measurements. CHUM FRY 38 Figure 1 8 . Seasonal behaviour changes, sockeye year l ings ; r e f e r to F i g . l6 f o r explanation of behaviour measurements. 39 Figure 1 9 . Seasonal b ehaviour changes, pink fryj refer to Fig. l6 for .explanation of behaviour measurements PINK FRY cr z> O ko k» Coho yearlings Three groups of coho yearlings exposed to d i f f e r e n t photoperiods were examined. The group exposed to a sixteen hour photoperiod was examined on three occasions. The control group (exposed to normal day lengths) and the eight hour group were each examined once. Figure 20 (Table XV) i l l u s t r a t e s the seasonal decline i n group behaviour shown by the sixteen hour f i s h . A c t i v i t y showed an i n i t i a l decline followed by a l a t e season increase. Like sockeye much of the increase (1+9.6$) was the d i r e c t r e s u l t of an accompanying increase i n aggressive behaviour. The control coho when tested i n June showed sim i l a r group behaviour to the sixteen hour f i s h , a s l i g h t l y greater a c t i v i t y and a considerably higher l e v e l of aggressive behaviour. This pattern as a whole more c l o s e l y resembles the behaviour shown by the sixteen hour f i s h i n l a t e August. This suggests that a sixteen hour photoperiod delays the c h a r a c t e r i s t i c decline i n a c t i v i t y and group behaviour and likewise i n h i b i t s the t y p i c a l l a t e season increase i n aggressive behaviour. The eight hour f i s h were examined i n l a t e July. Compared to the sixteen hour group (at t h i s time) they showed higher l e v e l s of a c t i v i t y and group behaviour and depressed aggressive behaviour. This pattern as a whole c l o s e l y resembles the behaviour complex shown by the sixteen hour group i n l a t e May. Apparently a short photoperiod delays but does not t o t a l l y i n h i b i t the development of the migratory behaviour complex. I l l F i g u r e 20. Seasonal behaviour changes, y e a r l i n g coho exposed to v a r i o u s photoperiods; r e f e r t o F i g . 16 f o r e x p l a n a t i o n o f behaviour measurements. COHO YEARLINGS of D o I UJ CD l.50r z l.25r O O x ^ I.OOr 5 0 -40f >-t 30h > < 10-o-10 8 6 4-2 CC ZD o X m UJ > L O LU Lt O O < • NORMAL PHOTOPERIOD O 16-HR. PHOTOPERIOD A 8 - HR PHOTOPERIOD O-JUNE | JULY | AUGUST jSEPTEMBER MAY 1+2 P. The Behavioural E f f e c t s of Somatotropin Injection Underyearling coho which had not undergone seaward migra-t i o n during the early summer were treated with mammalian soma-totropin. Injections were made t h r i c e weekly from August 13th to September 9 t h (13 i n j e c t i o n s ) . The average dose was 1 . 6 micrograms of somatotropin per gram of f i s h . Two groups of control f i s h were also tested. The f i r s t group was not injected. The second was injected with physiological saline. Figure 21 shows the r e s u l t s . Neither of the control groups showed a preference for seawater. The reason f o r the difference (approx. 10$) i n test compartment d i s t r i b u t i o n s of the two control groups was not c l e a r . In spite o f t h i s d i f f e r -ence the response i n s a l i n i t y and control experiments was s t a t i s t i c a l l y equivalent within each group. The response of the somatotropin group indicated a preference f o r hypertonic seawater s i g n i f i c a n t at the 10$ l e v e l but not at the 5$ l e v e l . The l e v e l of significance suggests that somatotropin may have a r e a l e f f e c t although the r e s u l t s of the present experiment must be regarded as inconclusive. The following factors probably operated to lessen the hormone e f f e c t s . Rather small doses were used and the i n j e c t i o n s stopped p r i o r to t e s t i n g s a l i n i t y preference. In addition physiological saline was used as the dilutant medium. Later i t was found that t h i s medium tended to p r e c i p i t a t e the p a r t i c u l a r hormone preparation used. kl Figure 21. E f f e c t s of somatotropin on s a l i n i t y preference of underyearling coho; chi-square indicates d i s t r i b u t i o n difference between s a l i n i t y and control experiments of hormoner: treated f i s h s i g n i f i c a n t at 10$ l e v e l O CONTROL EXP SALINITY EXP L U 6 0 -\— oc < CL O ^ 4 0 to LU r-I to LU 2 0 • O o 00 cq LU CC < ZD o to j_ . _ x u UNINJECTE D CONTROLS SALINE INJECTED CON TROLS SOMATOTROPIN TREATED FISH kk The r e s u l t s suggest a possible hormonal basis for the s a l i n i t y preference response. A more c r i t i c a l experimental examination i s warranted. The behavioural e f f e c t s of somatotropin are presented i n Pig. 22. Differences i n group behaviour were s l i g h t . The a c t i v i t y of the hormone injected f i s h was reduced to less than h a l f the values of both control groups. Aggressive behaviour was also reduced by more than one t h i r d . The significance of these changes w i l l require considerably more evaluation than possible i n the present preliminary examination. F i g u r e 22. B e h a v i o u r a l e f f e c t s o f somatotropin; r e f e r to F i g . l6 f o r e x p l a n a t i o n of : behaviour measurements. cc ZD O > I.50-< x LU CD O z |.25 8 x u CO, .OO IO 8 -6 -u < 4 -2 -O cr Q io x ft LU > LO CO LU CC O O < 8 -6 4 2 UNINJEC TED CONTROLS SALINE INJECTED CONTROLS SOMATOTROPIN TREATED Fl SH 1+6 IV. DISCUSSION A. Seasonal Behaviour Cycles Baggerman (i960) has demonstrated that s a l i n i t y prefer-ence follows seasonal cycles of development and regression i n juvenile P a c i f i c salmon. The data available to date (including Houston, 1956; Baggerman, i960 and the present study) permits the following generalizations. Chum, pink and sockeye develop a preference f o r hypertonic seawater as underyearlings. Coho f r y do not. When retained i n fr e s h water pink and sockeye lose t h i s preference i n the l a t e summer, i n contrast to chum f r y . As yearlings coho and sockeye show a hypertonic seawater preference during the normal period of migration aft e r which the preference i s l o s t . Three other aspects of behaviour show seasonal trends consistent i n the four species examined. During the expected period of migration and associated with a preference for hyper-tonic seawater, chum and pink f r y along with coho and sockeye yearlings showed high l e v e l s of a c t i v i t y and strong schooling tendencies. Aggressive behaviour during the same period was consistently low. Post migratory behaviour showed declining l e v e l s of a c t i v i t y and group behaviour combined with a marked development of aggressive a c t i v i t y . The interactions of these three aspects of behaviour were not examined. I t i s probably safe to say that the inverse seasonal r e l a t i o n s h i p of aggressive behaviour and a c t i v i t y contributed substantially to the changing schooling behaviour. Chum f r y under the p a r t i c u l a r experimental conditions showed the strongest schooling tendencies. The seasonal peak i n chum schooling coincided with the highest a c t i v i t y recorded fo r the four species and a complete absence of aggressive behaviour (nipping and chasing). The length of the da l l y photoperiod has been shown to be an important environmental factor i n timing seasonal behaviour changes. Baggerman ( i 9 6 0 ) has demonstrated that y e a r l i n g coho exposed to the Increasing day lengths of spring developed a preference for hypertonic seawater i n e a r l y A p r i l and retained the preference through May and June. Pish exposed to a long day length ( l 6 hours) developed a hypertonic seawater preference much e a r l i e r (February) than the controls. Continued exposure to these conditions produced a regression of the preference i n A p r i l and a second period of hypertonic seawater preference i n June. The group exposed to a short d a i l y photoperiod (8 hours) f a i l e d to develop a preference f o r hypertonic seawater. The r e s u l t s of the present studies confirmed the s a l i n i t y preference regression and redevelopment observed i n the 16 hour group above. An adequate explanation of how a long da i l y photoperiod acts p h y s i o l o g i c a l l y to produce two seasonal periods of saltwater preference i s lacking. Yearling coho exposed to a short d a i l y photoperiod i (8 hours) and tested In l a t e J u l y showed a strong preference f o r hypertonic seawater. A short d a i l y photoperiod apparently 1*8 delays but does not t o t a l l y i n h i b i t the change i n preference c h a r a c t e r i s t i c of migration. The length of the da i l y photoperiod also markedly affects other behaviour. Y e a r l i n g coho exposed to a long d a i l y photo-period ( 1 6 hours) from the previous December showed the follow-ing seasonal trends when tested i n May, July and August. Schooling behaviour showed a consistent seasonal decrease. A c t i v i t y decreased i n i t i a l l y but l a t e r increased. This l a t e season increase was an experimental a r t i f a c t the product of confining tanks associated with a high l e v e l of aggressive behaviour. Seasonally aggressive behaviour showed the reverse trend to a c t i v i t y and schooling behaviour. The increase i n aggressive tendencies was p a r t i c u l a r l y marked between July and August. The control group (exposed to natural day lengths) when tested i n June showed a behavioural complex which clo s e l y resembled that observed for the sixteen hour group i n l a t e August. A long d a i l y photoperiod apparently prolongs the high l e v e l s of a c t i v i t y and schooling behaviour c h a r a c t e r i s t i c of migration. I t also delays the post migratory increase i n aggressive behaviour. The group exposed to a short d a i l y photoperiod (8 hours) from the previous December was tested i n l a t e July. Their behaviour complex by contrast cl o s e l y resembled the sixteen hour group pattern of l a t e May. A short d a l l y photoperiod evidently delays development of the behaviour complex associated with migration. 1*9 In summary the period of seaward migration i n salmon i s characterized by a high l e v e l of a c t i v i t y , strong schooling behaviour, depressed aggressive behaviour as well as preference f o r hypertonic seawater. This pattern c l o s e l y matches Hoar's (195l»5>l4-»5>6,58) d e s c r i p t i o n of migratory behaviour i n juvenile P a c i f i c salmon. The length of the d a i l y photoperiod provides the major and common environmental timing device i n anadramous migration. The r o l e of other environmental variables i n t h i s regard has not as yet been examined. Northcote (i960) has shown that temperature plays an Important r o l e In resident rainbow trout migration. Photoperiods have also been shown to be of fundamental importance i n bird migration (Wolfson, i 960 ) . The nature of the control i s apparently d i f f e r e n t i n some respects. Unlike the r e g u l a r yearly migration of many birds, anadramous salmon trout and char may spend several years o f stream or lake residence p r i o r to seaward migration. The reproductive migration to fresh water likewise often follows a variable number of years i n the marine environment. Photoperiods, although of demonstr-able importance as an environmental aspect of a timing mechanism, appear to be modified by other fac t o r s as yet poorly known. T J B. Endocrine Factors The d i s t i n c t seasonal changes, both physiological and behavioural, associated with juvenile salmon migration are suggestive of an endocrine basis. The gland most studied i n 50 i n t h i s respect has been the thyroid. Hoar, Keenleyside and Goodall (1955) demonstrated that juvenile salmon treated with thyroxine showed an increased locomotor a c t i v i t y . Various androgens and oestrogens produced si m i l a r e f f e c t s . Baggerman (i960) examined the ef f e c t s of thyroxine and thyroid i n h i b i t o r s on s a l i n i t y preference. The administration of thyroxine to young salmon had no demonstrable eff e c t on s a l i n i t y preference. Thiourea and t h i o u r a c l l caused y e a r l i n g coho which prefered hypertonic seawater to lose t h i s preference. The significance of these r e s u l t s Is questionable since s t a t i s t i c a l l y dependent observations were added i n analyzing the data. This procedure had the ef f e c t of compound-ing rather small though i n some cases f a i r l y consistent d i f f e r -ences. Smith (1956) examined the effects of a large number of hormone preparations on s a l i n i t y tolerance i n brown trout (Salmo t r u t t a ) . Thyroxine administration produced rather v a r i a b l e r e s u l t s . He concluded as un l i k e l y that thyroxine plays a major r o l e In osmoregulation. The administration of mammalian somatotropin i n r e l a t i v e l y small (physiological) doses by contrast produced a consistent increase i n s a l i n i t y tolerance. The experimental f i s h were not hypophysectomized however and the treatment covered a period when the thyroid and other glands ( p i t u i t a r y , interrenal) are commonly active i n salmonids. The effects may have been synergistic rather than u n i l a t e r a l . Recent work by Olinerau (i960) has demonstra-ted that the i n t e r r e n a l i s active during the seaward migration 51 of juvenile A t l a n t i c salmon. Further both thyroxine and somatotropin play a role i n a c t i v a t i n g t h i s gland (Chartier-Baraduc, 1959; Fontaine and Leloup-Hatey, i960). In the present study a preliminary examination of the behavioural effects of mammalian somatotropin was made. Although the treated f i s h (stream resident underyearling coho) showed an increased preference f o r hypertonic seawater the r e s u l t s were not conclusive. The general l e v e l of a c t i v i t y and aggressive behaviour were also affected. Both showed appreciable decreases i n comparison to control groups. The increased preference f o r hypertonic seawater and depressed aggressive behaviour agrees with the t y p i c a l migration behaviour complex described above. These features may indicate the r o l e played by somatotropin i n seaward migration. A further evaluation of these r e s u l t s seems unwise at the moment. In summary i t may be stated that several endocrine organs are active at the time of migration. Further, d i s t i n c t e f f e c t s both physiological and behavioural have been obtained by administering variously p u r i f i e d endocrine preparations (Pickford and Atz, 1957* Hoar, 1959)* An adequate synthesis of these isolated effects w i l l require a thorough examination of endo-crine i n t e r a c t i o n . C. The Sensory Basis of S a l i n i t y Preference Houston (1956) and Hasler (1957) have reviewed the l i t e r a t u r e dealing with s e n s i t i v i t y of f i s h to dissolved s a l t s and other materials. Houston concluded that s a l i n i t y gradients may provide a di r e c t i v e influence f o r salmon migrations through 52 estuaries. I f s a l i n i t y gradients were to act as a d i r e c t i v e agency then a graded response to increasing s a l i n i t e s would be expected from downstream migrants. In the present work the response of chum salmon f r y to a series of seawater concentra-tions indicated an all-or-none rather than graded type of response. A consistently strong preference was shown f o r seawater concentrations from 5 /©©to 15 %* chloride. Below 1J.%OCT. no preference was shown. Evidently some mechanism other than s a l i n i t y gradients and s a l i n i t y preference provides the d i r e c t i v e influence In migration. The concentration at which the i n f l e c t i o n In response oceured (1L - 5&C1.) corresponds c l o s e l y to plasma chloride l e v e l s reported f o r Oncorhynchus masou (Kubo, 1955)* This suggests that plasma e l e c t r o l y t e l e v e l s may be the physio-l o g i c a l quantity on which s a l i n i t y preference hinges. The data indicate that chum f r y , a species n&ich migrates to sea shortly after emergence from the redd, prefer hypertonic but not hypotonic s a l t water. Houston (1956) showed that underyearling coho, normally stream residents at t h i s age, preferred hypotonic but not hypertonic seawater. Seaward migration involves a reversal i n preference from hypotonic to hypertonic s a l t water. The term "fresh water preference" used by e a r l i e r workers should be discarded. The close agreement between plasma e l e c t r o l y t e l e v e l s and the t o n i c i t y of the preferred seawater suggests a possible physiological basis for preference r e v e r s a l . Several workers 53 have noted that juvenile salmonids undergo a demineralization about the time migration commences (Page and Fontaine, 1958; Kubo, 1955). Both muscle and plasma el e c t r o l y t e l e v e l s are involved. The change from a hypotonic to a hypertonic prefer-ence may r e f l e c t a loss of e l e c t r o l y t e s . Laboratory rats under somewhat similar/ conditions (decreased e l e c t r o l y t e l e v e l s produced by adrenalectomy) show a strong preference f o r saline solution when given the choice of drinking either s a l t or fresh water. (Epstein and S t e l l a r , 1955) The all-or-none type of response to a series of seawater concentrations reveals a type of behavioural b a r r i e r . Some f i e l d observations by Hoar (1958) show that coho f r y , although normally stream residents as underyearlings, often move down-stream i n large numbers. Many f i s h enter brackish water but avoid more concentrated seawater. Black (195D bas shown that underyearling coho cannot osmoregulate i n hypertonic seawater. As mentioned above coho f r y prefer hypotonic but not hypertonic seawater. This pattern of preference provides a behavioural barrier which assures that the f i s h w i l l remain i n the hypotonic medium to which they are adapted. The reversal of preference associated with smoltation coincides with the development of the capacity to osmoregulate i n the hypertonic marine environment. The response of chum f r y to alterations i n the composition of seawater was examined i n an e f f o r t to i d e n t i f y the s p e c i f i c property to which they respond. This analysis also provided an Indirect means o f characterizing the sensory receptors involved i n the response. The following chemical manipulations did not a f f e c t the strong preference shown by chum f r y f o r natural seawater, (i ) elimination of the minor components of natural seawater by substituting an a r t i f i c i a l nine component s a l t water, ( i i ) the a l t e r a t i o n of the pH from 7 . 9 to 6.3, ( i i i ) the separate elimination of a l l cations except sodium and a l l anions except chloride. However when an osmotically equivalent sucrose solution was substituted f o r the standard a r t i f i c i a l seawater a negative response was obtained which was not s i g n i f i c a n t l y d i f f e r e n t from the control experiment. Indirect evidence suggests that the sweet taste of the sucrose solution did not contribute i n a major way to the negative response ( f i s h repeatedly entered the s o l u t i o n ) . This indicates that chum f r y , i n showing a preference f o r seawater, do not respond either to density or t o n i c i t y per se but rather to the concentration of s a l t s . The combined evidenoe indicates that sodium chloride alone probably provides an adequate stimulus. The extent to which other electrolytes may replace sodium chloride was not determined. The f a c t that t h i s electro l y t e i s the major constituent of both plasma and seawater suggests that under natural circumstances s a l i n i t y preference probably depends p r i n c i p a l l y on the concentration of sodium chloride. Two l i n e s of evidence indicate that the s a l i n i t y prefer-ence response i s c l o s e l y linked with plasma e l e c t r o l y t e s . It i s unlike l y however that the immediate response i s dependent on changes i n plasma e l e c t r o l y t e s . 55 The analysis of chum and sockeye s a l i n i t y preference response patterns showed that s i g n i f i c a n t d i s t r i b u t i o n s were frequently established during the i n i t i a l ten minutes of observation. I t i s important to note that seawater exposure during t h i s period was intermittent rather than continuous. Studies by Houston (1958) and Vickers (i960) indicate that appreciable changes i n plasma e l e c t r o l y t e s (flame photometric methods) are measured i n terms of hours rather than minutes. Both studies involved conditions of continuous exposure to hypertonic seawater solutions. This indicates that the immediate expression of a s a l i n i t y preference i s dependent on the stimulation of peripheral receptors. The effects of seawater concentration and composi-t i o n on s a l i n i t y preference point to a receptor sensitive to the concentration of s a l t s i n the medium. It i s impossible at the moment (and perhaps of l i t t l e consequence) to designate i t as an osmotic receptor s p e c i f i c a l l y s e n s i t i v e to the concen-t r a t i o n of s a l t s or as a gustatory s a l t receptor s e n s i t i v e to concentration differences. D. The B i o l o g i c a l Significance of S a l i n i t y Preference Considerable evidence has now been brought to bear on the idea that s a l i n i t y preference i s a prominent feature of juvenile salmon behaviour. Externally the response has been shown to depend on the stimulation of a receptor sensitive to the s a l t concentration of the medium. The discussion to follow i s an i n t e r p r e t a t i o n of the b i o l o g i c a l significance of s a l i n i t y preference i n terms of ecological implications and 56 underlying physiological mechanisms. Two d i s t i n c t phases of s a l t water preference have been demonstrated, one associated with resident stream existence, the other with the adoption of a marine existence. The stream phase i s characterized by a preference f o r water hypotonic to plasma e l e c t r o l y t e s . Hypertonic media are avoided. E a r l i e r work has shown that those species of salmon which remain i n streams for one or more years as juveniles are unable to regulate In hypertonic media during t h i s period (Huntsman and Hoar, 1939* Black, 1951)• A hypotonic preference ensures that the f i s h at th i s stage w i l l remain i n a medium to which they are osmotically adapted. For instance i n the event of a mistimed downstream displacement hypertonic media would be avoided. Smoltation and subsequent seaward migration i s character-ized by the change from a hypotonic to a hypertonic s a l i n i t y preference. A precise de s c r i p t i o n of the underlying physio-l o g i c a l causes responsible for t h i s change i n "motivation" i s not as yet possibl e . The following description forms a working hypothesis only. S a l i n i t y preference has been shown to be cl o s e l y related to plasma e l e c t r o l y t e l e v e l s . Smoltation involves a demineral-i z a t i o n and i t i s not u n l i k e l y that i n t e r n a l sensory stimuli a r i s i n g from osmotic receptors (a widespread vertebrate feature) could act d i r e c t l y on the ce n t r a l nervous system to modify s a l i n i t y preference. A p o s i t i v e response to a hypertonic medium i n a demineralized state would ensure a rapid r e s t o r a t i o n 57 of s a l t s . The f a c t that f i s h exposed to hypertonic seawater for twenty-four hours show a reduced though s t i l l p o s i t i v e preference for t h i s medium (Houston, 1956) suggests that t h i s mechanism may play a supporting r o l e i n the preference ohange associated with migration. Some other mechanism must act to maintain a hypertonic preference following r e s t o r a t i o n of plasma e l e c t r o l y t e s i n seawater. Several l i n e s of evidence suggest that the demineral-i z a t i o n associated with smoltation represents an endocrine mediated preadaptation to marine osmoregulation ( i ) as mentioned e a r l i e r the i n t e r r e n a l has been demonstrated to be active i n A t l a n t i c salmon smolts, ( i i ) the major mineralo corticords of higher vertebrates have been i d e n t i f i e d i n P a c i f i c salmon ( P h i l l i p s , Holmes and Bondy, 1959 )> ( i i i ) some of these p r i n -c i p l e s have been shown to play a ro l e compatible with osmo-regulation under marine conditions (Holmes, 1959)* The d i r e c t action of a hormone (either d i r e c t l y or i n d i r -e c t l y involved i n e l e c t r o l y t e metabolism) on the central nervous system to modify s a l i n i t y preference could also account f o r the close r e l a t i o n s h i p between demineralization and the change i n s a l i n i t y preference during smoltation. In addition i t could explain the continued preference for hypertonic seawater follow-ing r e s t o r a t i o n of plasma e l e c t r o l y t e s . Both thyroxine and somatotropin have been shown to play a ro l e i n i n t e r r e n a l a c t i v a t i o n (Fontaine, Leloup-Hatey, i960) and t h i s may account fo r the increased s a l i n i t y preference obtained with somatotropin i n the present study. The photoperiod mechanism presumably 58 a c t s v i a the hypothalmic p i t u i t a r y a x i s t o a c t i v a t e the endocrine system i n v o l v e d * The change from a hy p o t o n i c to a h y p e r t o n i c p r e f e r e n c e i s a s s o c i a t e d w i t h the development o f the c a p a c i t y to r e g u l a t e i n h y p e r t o n i c seawater. E c o l o g i c a l l y t h i s p r e f e r e n c e p a t t e r n i n s u r e s t h a t the f i s h o c c u p i e s a medium to which i t i s osmotic-a l l y adapted. T h i s b e h a v i o u r a l mechanism i s probably o f paramount importance f o r chum and p i n k f r y s i n c e these s p e c i e s show a very poor s u r v i v a l I n f r e s h water a f t e r the f r y stage. In summary, the change I n s a l i n i t y p r e f e r e n c e c h a r a c t e r -i s t i c o f s m o l t a t i o n r e p r e s e n t s the undoing o f the t e r m i n a l l i n k i n the c h a i n o f p h y s i o l o g i c a l and b e h a v i o u r a l events which p e r m i t s the abandonment o f the f r e s h water h a b i t a t i n favour o f a marine one. 59 V. SUMMARY 1. During the period of seaward migration the behaviour of juvenile P a c i f i c salmon shows; (a) a preference f o r seawater hypertonic to plasma e l e c t r o l y t e s , (b) a high l e v e l of general a c t i v i t y , (c) strong schooling behaviour, (d) depressed aggressive behaviour. 2. Post migratory behaviour changes (when retained i n fresh-water) include: (a) the development of a preference f o r water hypotonic to plasma e l e c t r o l y t e s , (except chum f r y ) (b) a gradual depression of general a c t i v i t y , (c) A gradual depression of schooling behaviour, (d) a marked increase i n aggressive behaviour. 3. The length of the d a i l y photoperiod i s an important mechan-ism i n timing seasonal behaviour changes* A long d a i l y photoperiod prolonged the behaviour c h a r a c t e r i s t i c of the migration period. A short photoperiod delayed these changes. Ii.. The all-or-none (rather than graded) s a l i n i t y preference response shown by chum f r y suggests that s a l i n i t y gradients probably do not act as d i r e c t i v e factors i n migration. 5« The expression of a preference f o r a p a r t i c u l a r t o n i c i t y i s dependent on the stimulation of a peripheral receptor sensitive to e l e c t r o l y t e concentration. 6. The response of chum f r y to alte r a t i o n s i n the composition of sea water suggests that under natural conditions s a l i n i t y preference i s dependent on the concentration of sodium chl o r i d e . 6o 7» The affects of somatotropin administered to underyearling coho included: (a) an increased although not s t a t i s t i c a l l y significant preference for hypertonic seawater (b) a depression of general activity (c) a depression of aggressive behaviour 8. Salinity preference operates as a behavioural mechanism to ensure that pre and post migratory stages of juvenile salmon occupy the medium to which they are osmotically adapted. 6i VI. LITERATURE CITED Baggerman, B. An experimental study of the t i m i n g o f breeding and m i g r a t i o n i n the t h r e e - s p i n e d s t i c k l e b a c k (Gasterosteus auculeatus L . ) , Auch. Neerland Z o o l . 12, io$-m (±WD Baggerman, B. The r o l e o f e x t e r n a l f a c t o r s and hormones i n m i g r a t i o n o f s t i c k l e b a c k s and j u v e n i l e salmon. "Comparative E n d o c r i n o l o g y " , E d i t e d by A. Gorbman. Wiley and Sons, New York, 2lj.-37 (1959) Baggerman, B. S a l i n i t y p r e f e r e n c e , t h y r o i d a c t i v i t y and the seaward m i g r a t i o n o f f o u r s p e c i e s o f P a c i f i c salmon (Oncorhyncus). J . P i s h . Res. Bd. Can. 17, 295-322 (I960) Barnes, H. Some t a b l e s f o r the i o n i c composition o f seawater. J . Exp. B i o l . , 31, 582-588 (1951) Black, V.S. Changes i n body c h l o r i d e , d e n s i t y and water content of chum (Oncorhyncus keta) and coho ( 0 . k i s u t c h ) salmon f r y when t r a n s f e r r e d from f r e s h water to sea water. J . P i s h . Res. Bd Can. 8 , I6I1 - I 7 6 (195D C h a r t i e r - B a r a d u c , M.M. I n f l u e n c e de I'hormone somatotrope sur l e s teneurs en eau et en e l e c t r o l y t e s du plasma et du muscle de l a T r u i t e a r c - e n - c i e l (Salmo  G a i r d n e r i i ) . Compt. rend. Soc. B i o l . 153, 1757-l 7 6 l Tl95*9) E p s t e i n , A.N. and S t e l l a r . The c o n t r o l of s a l t p r e f e r e n c e i n the adrenalectomized r a t . J . Comp. Psych. I4.8, 167-172 (1955) Page, L., Fo n t a i n e , M. M i g r a t i o n s , i n " T r a i t e de Z o o l o g i e " 13 (3), 1850-1881J., e d i t e d by P. Grasse, Masson, P a r i s , (1958) F o n t a i n e , M. and Leloup-Hatey, J . I n f l u e n c e de l ' a c t i v l t e m o t r i c e (nage a c o n t r e - c o u r a n t ) sur l a 17-hydroxy-c o r t i c o s t e r o i d e m i e de l a T r u i t e a r c - e n - c i e l (Salmo g a i r d n e r i i R i c h . ) . I n t e r v e n t i o n probable de de ce f a c t e u r dans 1 » a c t i v a t i o n de 1 ' I n t e r r e n a l a n t e r i e u r de jeune Saumon (Salmo s a l a r L.) pendant sa m i g r a t i o n d ' a v a l a i s o n . Compt. rend. Acad. Su P a r i s . 250, 3089-209l|. ( i 9 6 0 ) 62 H a s l e r , A.D. O l f a c t o r y and gu s t a t o r y senses o f f i s h e s " P h y s i o l o g y o f P i s h e s " . V o l . 2, E d i t e d by M.E. Brown. Academic P r e s s , N.Y. (1957) Hoar, W.S. The behaviour o f chum, p i n k and coho salmon i n r e l a t i o n t o t h e i r seaward m i g r a t i o n . J . P i s h . Res. Bd. Can. 8 , 21+1-263 (195D Hoar, W.S. The behaviour o f j u v e n i l e P a c i f i c salmon, w i t h p a r t i c u l a r r e f e r e n c e to sockeye (Oncorhynous nerka) J . P i s h . Res. Bd. Can. 11, 69-97 (195^) Hoar, W.S. The behaviour o f m i g r a t i n g p i n k and chum salmon f r y . J . P i s h . Res. B d. Can. 13, 309-325 (1956) Hoar, W.S. Rapid l e a r n i n g of a constant course by t r a v e l l i n g s c h o ols o f j u v e n i l e P a c i f i c salmon. J . P i s h . Res. Bd. Can. 15, 251-271+ (1958) Hoar, W.S. The e v o l u t i o n o f mi g r a t o r y behaviour among j u v e n i l e salmon of the genus Oncorhynous. J . P i s h . Res. Bd Can. 13, 391-1+28 (1958) Hoar, W.S. End o c r i n e f a c t o r s i n the e c o l o g i c a l a d a p t a t i o n of f i s h e s . "Comparative E n d o c r i n o l o g y " . E d i t e d by A* Gorbman. John Wiley and Sons, New York, 1-23 (1959) Hoar, W.S., K e e n l e y s i d e , M.H.A. and G o o d a l l , R.G. The e f f e c t s o f t h y r o x i n e and gonadal s t e r o i d s on the a c t i v i t y o f salmon and g o l d f i s h . Can. J . Z o o l . 3 3 , 1+28-1+39 (1955) Holmes, W.N. S t u d i e s o f the hormonal c o n t r o l o f sodium meta-b o l i s m i n the rainbow t r o u t (Salmo g a i r d n e r i ) A c t a E n d o c r i n o l o g i c a 31, 5 8 7 - 6 0 2 (19^91 Houston, A.H. Responses o f j u v e n i l e chum, p i n k and coho salmon to sharp seawater g r a d i e n t s . Can. J . Z o o l . 35» 371-383 (1956) Houston, A.H., Locomotor performance and osmoregulation i n j u v e n i l e anadramous salmonids f o l l o w i n g abrupt environmental s a l i n i t y change. Ph D. T h e s i s , Dept. Z o o l . Univ. B r i t i s h Columbia, Vancouver (1958) Hunstsman, A.G. and Hoar, W.S. R e s i s t a n c e o f A t l a n t i c salmon to seawater. J . P i s h . Res. Bd. Can. 1+, 1+09-1+11 1939 K e e n l e y s i d e , M.H.A. Some as p e c t s o f the s c h o o l i n g behaviour o f f i s h . Behaviour. 8 , 183-21+8 (1955) 63 Kubo, T. Changes of some c h a r a c t e r i s t i c s of blood of smolt of Oncorhynous masou during seward migration. B u l l , Pac. Pish. Hokkaido Univ. 6, 201-207 (1955) Northcote, T.G. Migratory behaviour of juvenile rainbow trout Salmo gairdneri i n outlet and i n l e t streams of Loon Lake, B r i t i s h Columbia. Ph. D. Thesis, Univ. B r i t i s h Columbia, Vanoouver. (i960) Oliverau, M. Etude volumetrique de 1»interrenal anterieur ceu cours de l a s m o l t i f i c a t i o n de Salmo salar L., Acta Endocr. 33, 11+2-156 (i960) P h i l l i p s , J.G., Holmes, W.N..and Bondy, P.K. Adrenocorti-costeriods i n salmon plasma (Oncorhynchus nerka). Endocrinology 5, 8II-818 (1959") Pickford, G.E. and Atz, J.W. The physiology of the p i t u i t a r y gland of fi s h e s , New York Zool S o c , New York. (1957) Smith, D.C.W. The r o l e of endocrine organs i n the s a l i n i t y tolerance of trout. Mem. Soc. Endocrin. 5» 83-9° (1956) V I I . APPENDIX TABLE V I I I . SEASONAL AND EXPERIMENTAL SALINITY PREFERENCE DATA CHUM FRY 1 C o n t r o l j Experiments 1 Standard A r t i f i c i a l Sea Water Experiments 27.1%° S a l i n i t y M i s c e l l a n e o u s T e s t S o l u t i o n s Number o f Date % D i s t r i b u -t i o n T e s t Compart-ment C h i -square % D i s t r i b u -t i o n Test Compart-ment C h i -square % D i s t r i b u -t i o n T e s t Compart-ment C h i -square Test S o l u t i o n E x p e r i -mental R e p l i c a -t i o n s May 17-20 1+1.7 - 2 .66 - - 5 6 . 0 7.9I+ N a t u r a l sea water 25 . I j -X s a l i n i t y 12 May 3 1 -June ij. 3 8 . 6 - 1L.20 60.8 16.7 6ii.O 21.70 » 10 June 15-19 kk-k - 1.01 57.8 6.01 5if.8 3.55 One anion only c h l o r i d e - e q u i v a -l e n t to 2$.\\%0 s a l i n i t y . 10 June 2 9-July 5 . 1+3.1 - 2 .88 61 .IJ, 1 3 - 7 0 59.8 11.02 One c a t i o n only sod ium- equiv a-l e n t to 2 5 4 %> s a l i n i t y . 12 J u l y 21-2^ - - 5 8 . 3 - 56.8 - A r t i f i c i a l Sea water pH6.3,25.1^ s a l i n i t y 12 J u l y 29-Aug.3 3 6 . 2 - 7.37 — - 61.2 2 6 . 0 A r t i f i c i a l sea water 10.9%. s a l i n i t y 12 TABLE V I I I . (CON'T) SEASONAL AND EXPERIMENTAL SALINITY PREFERENCE DATAA CHUM FRY C o n t r o l Experiments Standai A r t i f i c i s water Exj 27.1%oSa] i l sea >eriment U n i t y M i s c e l l a n e o u s T e s t S o l u t i o n s Number of E x p e r i -mental R e p l i c a -t i o n s Date % D i s t r i -b u t i o n T e s t Compart-ment C h i -square % D i s t r i -b u t i o n T e s t Compart-ment C h i -square % D i s t r i -b u t i o n Test Compart-ment C h i -square Test S o l u t i o n J u l y 29-Aug.3 - - - - 27.6 - 3.01+ Sucrose s o l u t i o n e q u i v a l e n t 10.9%° s a l i n i t y 12 Aug. 8-13 3if.O - 9 .76 5 6 . 5 2 1 4 5 3 8 . 6 0.86 A r t i f i c i a l sea water 3»l%o s a l i n i t y 12 Aug . 2 9-Sept . 3 1*6.7 - 0 4 3 65.7 13 . 8 6 1+7.0 0.00l| A r t i f i c i a l sea water 7«3%o s a l i n i t y 12 Sept. 5-10 30.9 -13 .95 - - 59-9 3 7 . 6 L L A r t i f i c i a l sea water 18.1 s a l i n i t y 12 Sept. 5-10 - - - - 5 6 . 5 29.28 A r t i f i c i a l sea water 9.1%o s a l i n i t y 12 TABLE IX. SEASONAL BEHAVIOUR DATA CHUM FRY Date Average (Active) Group Size A c t i v i t y Average Number of P a r t i t i o n Crossings Per 5 Min.Obs^rva-fa t l o n Aggressive Behaviour Average Number of Act ions Per 5 Min. Observation Ind iv idua l s Groups Nipping Chasing May 31- June II 1.58 20.35 12.86 0.1+3 0.06 June 15-19 2.12 I16.IO 21.55 0.12 0.00 June 29-July 5 2.26 lj.9.00 21.70 0.00 0.00 July 21 -2li 1+0.35 16.72 0.00 0.00 July 29-Aug.3 2.27 32.30 l if .23 0.21 0.06 Aug. 8-13 I .96 31.85 16.25 0.32 0.07 Aug. 29-Sept.3 1.26 19.75 15.70 3.79 1.25 Sept. 5-10 1.10 10.31+ 9 . i t l If.12 1.73 TABLE X. SEASONAL SALINITY PREFERENCE SOCKEYE YEARLINGS C o n t r o l S a l i n i t y Experiment Number Experiment N a t u r a l Seawater 2 5 , ± 1 % . S a l i n i t y o f % % E x p e r i m e n t a l Date D i s t r i b u t i o n D i s t r i b u t i o n T e s t Chi-square T e s t Chi-square R e p l i c a t i o n s Compartment Compartment June 6 , 8 , 1 0 , 1 2 3 2 . 9 - 1 1 . 2 2 5 5 . 3 2 1 . 8 3 1 2 J u l y 8,10,12,14 2 5.3 -23.1+0 1+2.1 ll+.30 1 2 Aug. 1 8 , 2 2 , 2 5 , 3 5 . 0 - 8.61+ 5 5 . 1 1 6 . 8 8 1 2 2 7 TABLE XI. SEASONAL BEHAVIOUR DATA SOCKEYE YEARLINGS A c t i v i t y Aggressive Behaviour Date Average Active Group Size Average number Crossings Per Observations of p a r t i t i o n 5 min. Average Number of Actions Per 5 min. Observation Individuals Groups Nipping Chasing June 6 , 8 , 1 0 , 1 2 1 . 2 3 1 1 . 7 2 9 . 5 3 0 . 8 1 0.1+8 July 8,10,12, lit l . l i j . 6.J+2 5 . 6 3 1 .73 O .96 Aug. 1 8 , 2 2 , 2 5 , 27 1 . 12 24.28* 2 1 . 3 8 6 . 9 8 2 . 3 8 2 7 . 6 $ Forced a c t i v i t y due to high l e v e l of aggressive behaviour. TABLE X I I . SEASONAL SALINITY PREFERENCE PINK FRY C o n t r o l E x p e r i m e n t S a l i n i t y E x p e r i m e n t N a t u r a l S e a w a t e r 25 + 1%. S a l i n i t y D a t e D i s t r i b u t i o n D i s t r i b u t i o n 5'est C h i - s q u a r e T e s t C h i - s q u a r e Compartment Compartment Number o f E x p e r i m e n t a l R e p l i c a t i o n s J u n e 23-26 3if .2 - 9*6LL 61.7 32.27 12 Aug. l l | . , l 6 , 2 0 , 23 39.3 - Ii . i i 2 JJJ4.3 0.99 12 S e p t . 2 1 , 2 l i , 2 7 , 30 20.1 -31+.3 27.5 1.33 12 TABLE XIII. SEASONAL BEHAVIOUR DATA PINK FRY A c t i v i t y Aggressive Behaviour Date Average Active Group Size Average Number of P a r t i t i o n Crossings Per 5 min. Observation Individuals Groups Average Number of Actions Per 5> min. Observation Nipping Chasing June 23-26 1.17 9.72 8.31 0.17 O.06 Aug. l i t , 16,20,23 1.07 6.17 5.79 2.33 0.56 Sept. 21,2IL,27, 30 1.01 l f . 5 0 5.73 1.8/4 TABLE XIV. SEASONAL SALINITY PREFERENCE YEARLING COHO EXPOSED TO VARIOUS PHOTOPERIODS Control Experiment S a l i n i t y Experiment Natural Sea Water 25 ±|%o S a l i n i t y Number of Length of Date Daily Photoperiod i D i s t r i b u t i o n Test Compartment Chi-square % D i s t r i b u t i o n Test Compartment Chi-square Experimental Replications May 26-29 16 hours 32.9 - 1 0 . 2 0 32.5 - 0 . 0 1 12 Natural June 5 , 7 , 9 , 1 1 Day Lengths i49.i1' - 0 .01 k9-k 0.00 12 July 7 , 9 , 1 1 , 16 hours 13 33.7 -IO.9I* 50 .3 12.80 12 July 25-28 8 hours 1*6.2 - 0.57 59.2 6.55 12 Aug. 1 5,17 , 2 1 , . , , 21L,26,28 1 6 h o u r s 1*1*.8 - 1.38 5 0 . 5 1.82 18 TABLE XV. SEASONAL BEHAVIOUR DATA YEARLING COHO EXPOSED TO VARIOUS PHOTOPERIODS Length of Average A c t i v i t y Aggressive Behaviour Date Daily Photoperiod Active Group Size Average Number t i o n Crossings Observation of P a r t i -Per 5 Min. Average Number of Actions Per 5 Min. Observation Individuals Groups Nipping Chasing May 26-29 l6 hours 1.28 6.22 4.86 1.02 0.65 June 5,7,9.11 Natural day lengths 1.27 9.25 7.27 4.48 4.08 July 7,9»H»13 l6 hours 1.17 3.02 2.58 1.11 1.17 July 25-28 8 hours 1.31 13.46 10.30 1.04 0.77 Aug. 15,17. 21,2IL,26,28 l6 hours 1.07 IO.69* 9-97 5.21 2.2li 49.6$ Forced A c t i v i t y Due to High Level of Aggressive Behaviour 

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