@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Zoology, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Houston, Arthur Hillier"@en ; dcterms:issued "2012-02-03T20:06:02Z"@en, "1956"@en ; vivo:relatedDegree "Master of Arts - MA"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """The responses of chum and pink salmon fry, and coho salmon fry and smolts (Oncorhynchus keta, O. gorbuscha, and O. kisutch) to isotonic and hypertonic seawater were studied in sharp-gradient tanks to determine whether or not salinity gradients can act as directive agencies in the seaward migration of juvenile Pacific salmon. Chum and pink fry responded positively to both concentrations of seawater. Coho fry responded positively to isotonic seawater but did not respond positively to hypertonic seawater. Coho smolts responded positively to hypertonic seawater. Acclimation of chum fry to seawater prior to observation of their responses resulted in a reduction of their initial response although there was no significant change in the levels of response finally obtained. Major differences in the concentration of the acclimatory solutions did not affect the responses of this species to hypertonic seawater. The activity of chum and pink fry, and of coho smolts generally decreased on first entry into seawater. Observations on acclimated chum fry suggest that activity is related to osmotic control. Decreased activity may arise from the interaction of absorbed electrolytes on muscle protein. This effect continues until the commencement of osmoregulation when excess absorbed ions are removed from the muscles. The relatively high levels of activity observed in pink fry may be the result of hyperfunction of the thyroid gland, a condition related to osmotic stress in fresh water. The influence of sea water on the seaward movements of juvenile Pacific salmon is probably two-fold. The effects of absorbed electrolytes on motor activity may decrease the intensity of rheotrophic responses which would tend to keep the migrants in river mouths, while at the same time increasing the probability of passive displacement out to sea by current action. Active positive responses to salinity gradients enhance the likelihood of movement into the ocean. Control experiments indicated the operation of some factor or factors resulting in preference reactions by chum and pink fry and coho smolts for the tanks in which they had been originally placed. The possible influence of olfactory and visual cues on this preference reaction has been discussed."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/40484?expand=metadata"@en ; skos:note "AN EXPERIMENTAL STUDY OF THE RESPONSE OF YOUNG PACIFIC SALMON TO SHARP SEA WATER GRADIENTS by ARTHUR HILLIER HOUSTON B.Sc, McMASTER UNIVERSITY, 1954 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Zoology We accept t h i s thesis as conforming to the standard required from candidates f o r the degree of MASTER OF ARTS Members of the Department of Zoology • THE UNIVERSITY OF BRITISH COLUMBIA February, 1956 - i i -ABSTRACT The responses of chum and pink salmon f r y , and coho salmon f r y and smolts (Oncorhynchus keta, 0^ gorbuscha, and 0^ kisutch) to isotonic and hypertonic seawater were studied i n sharp-gradient tanks to determine whether or not s a l i n i t y gradients can act as d i r e c t i v e agencies i n the seaward migration of juvenile P a c i f i c salmon. Chum and pink f r y responded p o s i t i v e l y to both concentrations of seawater. Coho f r y responded p o s i t i v e l y to isotonic seawater but did not respond p o s i t i v e l y to hypertonic seawater. Coho smolts responded p o s i t i v e l y to hypertonic seawater. Acclimation of chum f r y to seawater p r i o r to observation of t h e i r responses resulted i n a reduction of t h e i r i n i t i a l response although there was no s i g n i f i c a n t change i n the le v e l s of response f i n a l l y obtained. Major differences i n the concentration of the acclimatory solutions did not eff e c t the responses of t h i s species to hypertonic seawater. The a c t i v i t y of chum and pink f r y , and of coho smolts generally decreased on f i r s t entry into seawater. Observations on acclimated chum f r y suggest that a c t i v i t y i s related to osmotic control. Decreased a c t i v i t y may ar i s e from the i n t e r a c t i o n of absorbed e l e c t r o l y t e s on muscle protein. This e f f e c t continues u n t i l the commencement of osmoregulation when excess absorbed ions are removed from the muscles. The r e l a t i v e l y high l e v e l s of a c t i v i t y observed i n - i i i -pink f r y may be the r e s u l t of hyperfunction of the thyroid gland, a condition related to osmotic stress i n fresh water. The influence of sea water on the seaward movements of juvenile P a c i f i c salmon i s probably two-fold. The eff e c t s of absorbed e l e c t r o l y t e s on motor a c t i v i t y may decrease the i n t e n s i t y of rheotrophic responses which would tend to keep the migrants i n r i v e r mouths, while at the same time increasing the p r o b a b i l i t y of passive displacement out to sea by current action. Active positive responses to s a l i n i t y gradients enhance the l i k e l i h o o d of movement into the ocean. Control experiments indicated the operation of some factor or factors r e s u l t i n g In preference reactions by chum and pink f r y and coho smolts f o r the tanks i n which they had been o r i g i n a l l y placed. The possible influence of olf a c t o r y and v i s u a l cues on t h i s preference reaction has been discussed. - i x -ACKNOWLEDGEMENTS The author wishes to express his sincere gratitude to Prof. W.S. Hoar, Department of Zoology, f o r providing funds, and supervision of t h i s research. He also wishes to thank Prof. E.C. Black, Department of Physiology, Prof. W.A. Clemens, Director of the In s t i t u t e of Oceanography, Prof. Milton Kirsch, Department of Chemistry, Prof. P.JU Larkin, Director of the In s t i t u t e of Fisheries, and Prof. C C . Lindsay, Department of Zoology, f o r advice received on various aspects of the in v e s t i g a t i o n . He i s indebted to Dr. F e r r i s Neave of the P a c i f i c B i o l o g i c a l Station, Nanaimo, B r i t i s h Columbia, f o r pink salmon f r y used i n t h i s research, and to Mr. M.A. Newman fo r c o l l e c t i o n of coho salmon smolts. Scholarships awarded by the Research Council of Ontario, and the Fisheries Research Board of Canada made the study possible. - i v -TABLE OF CONTENTS PAGE I. INTRODUCTION 1 I I . REVIEW OF LITERATURE 3 A. ETHOLOGICAL ASPECTS OF MIGRATION 3 (1) Downstream Migration of P a c i f i c Salmon Fry. 3 (2) Departure Stimuli 6 (3) Directive Factors Other Than S a l i n i t y Gradients 7 (4) Response to S a l i n i t y Gradients S B. PHYSIOLOGICAL ASPECTS OF MIGRATION 12 (1) S e n s i t i v i t y of Fishes to Variations i n Sa l t Content 12 (2) Physiological Changes P r i o r to Migration .. 14 (3) Influence of Endocrine Function on - Migration • 15 I I I . MATERIALS AND METHODS 20 Materials 20 Methods 20 Apparatus 22 Test Solutions 28 Chemical Methods 30 Procedure 30 Studies Carried Out 32 Analysis of Data 33 Data i n Appendix 36 - V -TABLE OF CONTENTS (Continued) PAGE IV. RESULTS 37 CHUM SALMON FRY 37 A. Observations on Behaviour '37 B. Control Experiments 39 C. Reactions of Unacclimated Fry to Seawater . . 3 9 D. E f f e c t s of Acclimation to Seawater on Response to Seawater 42 E. A c t i v i t y 46 PINK SALMON FRY 51 A. Observations on Behaviour 51 B. . Control Experiments 54 C. Reactions of Fry to Seawater ............... 54 D. A c t i v i t y 56 COHO SALMON FRY AMD SMOLTS 60 FRY: A. Observations on Behaviour 60 B. Control Experiments 62 C. Reactions of Fry to Seawater 62 D. A c t i v i t y 64 SMOLTS: A. Observations on Behaviour 67 B. Control Experiments 67 C. Response to Hypertonic Seawater 68* D. A c t i v i t y 63 v i -TABLE OF CONTENTS (Continued) PAGE V. DISCUSSION 73 Behaviour During Control Experiments 73 S e n s i t i v i t y to Seawater 75 E f f e c t of Seawater on A c t i v i t y 76 Reactions of Pink Salmon Fry Compared With Other Species . $3 Responses of Coho Salmon Fry and Smolts to Seawater 85 \"Exploratory\" and \"Preference\" A c t i v i t y ...... 86 Decrease i n Response With Time 87 Relationship of Seawater to Seaward Migration #8 VI. SUMMARY 90 VII. LITERATURE CITED 91 VIII. APPENDIX '. 97 i - v i l -li 1ST OF FIGURES FIGURE PAGE 1. Photograph of apparatus 23 2. Diagram of apparatus 24 3 . Typical temperature profi le 26 4. Rise in sa l in i ty of freshwater compartments . 26 5. I n i t i a l water exchange between compartments . 29 6. Typical sa l in i ty profi le at 200 minutes .29 7. Response of unacclimated chum salmon fry to .• seawater 40 S. Response of chum salmon fry to isotonic seawater following acclimation to hypertonic seawater 43 9. Response of chum salmon fry to hypertonic seawater following acclimation 45 10. Act ivi ty of unacclimated chum salmon fry 47 11. Activity-response relationship in unacclimated chum salmon fry 49 12. Act iv i ty of acclimated chum salmon fry 50 13. Activity-response relationship in acclimated chum salmon fry 52 14. Response of pink salmon fry to seawater 55 15. Act iv i ty of pink salmon fry . . . 57 16. Activity-response relationship i n pink salmon fry 59 17. Response of coho salmon fry to seawater 63 18. Act iv i ty of coho salmon fry 65 19. Activity-response relationship in coho salmon fry 66 20. Response of coho salmon smolts to seawater . . . 69 21. Act iv i ty of coho salmon smolts 71 22. Activity-response relationship in coho salmon smolts 72 - v i i i -LIST OF TABLES TABLE PAGE I. Data on experimental salmon 21 I I . Data on chum salmon f r y experiments 3& I IT. Data on pink salmon f r y experiments 53 TV. Data on coho salmon f r y and smolt experiments .. 61 V. Control data and response of chum salmon f r y to isotonic seawater 98 VI. Comparison of responses of chum salmon f r y to isotonic seawater 99 VII. Response of chum salmon f r y to hypertonic seawater 100 VIIIA. Comparison of responses of chum salmon f r y to hypertonic seawater . .• 101 VIIIB. Comparison of responses of chum salmon f r y to hypertonic seawater 102 IX. Control data and response of pink salmon, f r y to seawater 103 X. Comparison of responses of pink salmon f r y to seawater 104 XI. Control data and response of coho salmon f r y to seawater .105 XII. Comparison of responses of coho salmon f r y to seawater 106 XIII. Control data and response of coho salmon smolts to seawater 107 XIV. Comparison of responses of coho salmon smolts .. 108 XV. A c t i v i t y of unacclimated chum salmon f r y 109 XVI. A c t i v i t y of acclimated chum salmon f r y 110 XVII. A c t i v i t y of pink salmon f r y I l l XVIII. A c t i v i t y of coho salmon f r y 112 XIX. A c t i v i t y of coho salmon smolts 113 XX. Tests of homogeniety of variance 114 INTRODUCTION It i s u n l i k e l y that the migrations of fis h e s are aimless wanderings, hence t h e i r movements must be influenced by d i r e c t i v e agencies, \"... those factors which allow or require a metabolic response on the part of the organism directed i n some r e l a t i o n to a gradient of the factors ...\" (Fry, 1947)'. The operation of such factors depends on t h e i r natural occurrence, the a b i l i t y of the fishes to detect changes i n t h e i r i n t e n s i t y or concentration, and the presence of oriented responses to these gradients. Work by Hoar on P a c i f i c salmon (Oncorhynchus spp.),. and Fontaine on the European e e l (Anguilla a n g u i l l a Shaw) and the A t l a n t i c salmon (Salmo s a l a r Linnaeus) make i t apparent that rheotactic responses are the predominant factors i n the freshwater portion of the migration of these f i s h e s . It i s u n l i k e l y that s a l i n i t y gradients exercise any important effects on the movements of f i s h while they are i n lakes and r i v e r s . Fontaine and Vibert (1952), investigated the concentration of dissolved s o l i d s i n the waters of the Adour River system, France., and came to the conclusion that the gradients which occurred were not necessarily important i n the downstream migration of A t l a n t i c salmon. Their opinion was based on two observations, the i r r e g u l a r i t y of the gradient under the influence of t r i b u t a r i e s , and the low rate of change i n concentration with distance. They believed the l a t t e r to be below the known l e v e l of s e n s i t i v i t y of f i s h e s . - 2 -It i s probable that a s i m i l a r s i t u a t i o n prevails i n the r i v e r systems of the P a c i f i c coast of Canada. S a l i n i t y gradients become potential d i r e c t i v e factors i n seaward migration i n r i v e r mouths and estuaries, since i n these regions the d i r e c t i v e capacity of r i v e r currents i s decreased by loss i n speed, and i n constancy of d i r e c t i o n . The continued movement of f i s h through such areas argues the operation of some other factor, such as a chemical gradient. The existence of r e l a t i v e l y sharp s a l i n i t y gradients, i e . those i n which the v a r i a t i o n i n s a l t content with distance appears to be within the sensory capacity of most fish e s , have been demonstrated by recent oceanographic investigations on-the P a c i f i c coast ( F j a r l i e 1950, Waldichuk 1952, F i s h e r i e s Research Board of Canada 1953, Tabata 1954), and i t i s the purpose of t h i s thesis to investigate t h e i r importance as d i r e c t i v e agencies i n the seaward migration of P a c i f i c salmon f r y and smolts. REVIEW OF LITERATURE A. ETHOLOGICAL ASPECTS OF MIGRATION (1) Downstream Migration of P a c i f i c Salmon Fry The ethological aspects of the downstream migration of P a c i f i c salmon f r y (Oncorhynchus spp.) have been c l a r i f i e d by Hoar and other in v e s t i g a t o r s . In recent years Hoar has studied experimentally the behaviour of pink salmon fry, (Oncorhynchus gorbuscha (Walbaum)),. chum salmon f r y , {0^ keta (Walbaum)), and coho salmon f r y and smolts {0^ kisutch (Walbaum)), (Hoar, 1951 a, 1953> 1954, 1956, Keenleyside and Hoar 1954, MacKinnon and Hoar 1953)• Of these the pink and chum salmon usually migrate to sea shortly a f t e r t h e i r emergence from the redds. Coho f r y , on the other hand, tend to remain f o r at l e a s t one year i n freshwater before migrating seaward. Chum and pink f r y were found to exhibit high l e v e l s of a c t i v i t y both day and night. During the day they maintain p o s i t i o n i n water currents through well developed p o s i t i v e rheotropism. However, at night, with v i s u a l s t i m u l i no longer available, and the importance of contact s t i m u l i decreased by a tendency to r i s e to the surface, the f i s h are swept downstream. This inovement i s enhanced by the response of the f r y to current, since they tend to display a marked preference for strong currents (MacKinnon and Hoar 1953) . Keenleyside and Hoar (1954) demonstrated the existence of another pattern of behaviour which may be important i n - 4 -migratory movements. At high temperatures and high rates of change of temperature the rheotrophic response of chum f r y becomes negative; under these conditions they swim with currents rather than against them. By contrast, the behaviour of coho f r y i s such as to reduce the p o s s i b i l i t y of downstream movement. The most ch a r a c t e r i s t i c feature of t h e i r behaviour i s a tendency to occupy and defend t e r r i t o r i e s . At night t h e i r a c t i v i t y decreases and the f i s h s e t t l e on the bottom. This nocturnal reduction of a c t i v i t y i s accompanied by a r e l a t i v e l y high threshold of stimulation. Their reaction to current i s less pronounced than that of chum f r y (MacKinnon and Hoar 1953). Contrasting the behaviour of chum and pink f r y with coho f r y i t i s not d i f f i c u l t to see why the l a t t e r species remains i n r i v e r s and lakes. During parr-smolt transformation d i s t i n c t changes i n the behaviour of young coho are apparent. They lose t h e i r strong t e r r i t o r i a l reaction, develop schooling tendencies, and exhibit a lower stimulation threshold at night. These changes plus an increasing tendency to surface at night and development of a more marked p o s i t i v e rheotropism, r e s u l t i n a gradual seaward movement of the smolts. More recently Neave (1955)> studied pink and chum salmon migrants i n the f i e l d , and published results disagreeing with those of Hoar (1951, 1953) and MacKinnon and Hoar (1953). He described pink f r y newly emerged from t h e i r redds as being completely i n a c t i v e during the day, with a tendency to bury - 5 -themselves i n the gravel of stream bottoms u n t i l l a t e evening. Their natural response to current was described as negatively rheotactic, the f i s h moving a c t i v e l y with the current and as i n d i v i d u a l s , rather than i n schools. He concluded that \"... the responses recorded by Hoar and MacKinnon are c h a r a c t e r i s t i c of f r y at a period a f t e r migration would have been completed ...\" and suggested that changes i n the behaviour of f r y a f t e r schooling might be associated with the development of feeding habits. In a s t i l l l a t e r paper Hoar (1956) established that differences did ex i s t between the behaviour of f r y which had schooled and those which had not schooled. Hoar did not f e e l that these changes i n behaviour were attributable to the commencement of feeding, or to changes- i n phototactic or rheotactic responses. He postulated that the observed differences were i n some way associated with the operation of the f r y as a school. This investigation also produced evidence f o r an orientated d i r e c t i o n of migration, and minimized the importance of rheotaxis i n f r y which had not schooled. The causal factors behind the establishment of the d i r e c t i o n of migration, either with or against current, were not developed and remain open to speculation. Hoar concluded that the behaviour patterns previously determined i n the laboratory were c h a r a c t e r i s t i c of schooling f r y , and therefore applicable to the l a t t e r stages of migration but not to the period before schooling had commenced. - 6 -(2) Departure Stimuli Some data are available on the i n i t i a l stimulus or stimuli preceding downstream migration of P a c i f i c and A t l a n t i c salmon. Huntsman (194#a) related the departure of the l a t t e r f i s h from r i v e r s and streams to l o c a l p r e c i p i t a t i o n which produced high water and swift currents. White (1940), on the other hand, believed that the descent of A t l a n t i c salmon smolts was more c l o s e l y a l l i e d to changes i n temperature and the occurrence of low l i g h t i n t e n s i t i e s than to r i s e s i n water l e v e l . Temperature appears to be an important f a c t o r i n the movement of P a c i f i c salmon. Foerester (1937) found that the seaward movement of Cultus Lake, B r i t i s h Columbia, sockeye smolts (Oncorhynchus nerka (Walbaum)) was associated with a r i s e i n the temperature of the surface water to 4«5°C -o 5.5 C Shapovalov and Taft (1954) noted that there was a relati o n s h i p between spring water l e v e l and the downstream movement of steelhead trout (Salmo g a i d n e r i i g a i d n e r i i Richardson) and coho salmon. They suggested that high temperatures and.light might be important i n i n i t i a t i n g migration. Hoar (1953) also mentioned that the o r i g i n a l departure stimulus might be l i g h t , a photoperiodic e f f e c t acting through the p i t u i t a r y gland to i n i t i a t e parr-smolt transformation. The physiological aspects of migration w i l l be discussed more f u l l y i n a l a t e r section. - 7 -(3) Directive Factors Other Than Sal ini ty Gradients A considerable body of evidence is available indicating that gradients in the physical and chemical qualit ies of water may influence the orientation of f ishes. Data drawn from Doudoroff (193$) indicate that Gire l la nigricans (Ayres), the Cal i fornia bluefish, exhibits a marked preference for narrow ranges of temperature. This response was found to be dependent, to some extent, on the previous thermal history of the individuals. Investigations by Fry (1947) on the goldfish (Carassius auratus Linnaeus) corroborated this point. Coll ins (1952), in studying the importance of temperature and carbon dioxide as directive factors in the riverward migration of the sexually maturing adults of two anadromous species, the alewife (Pomolobus pseudoharengus (Wilson)) and the glut herring (P^ aest ival is (Mi tch i l l ) ) , found that these f ish consistently chose the warmer of two streams (when temperature differences exceeded 0.5 centigrade degrees) and the least concentrated solution of carbon dioxide (when the concentration differences were greater than 0.3 p.p.m.). The relative orienting influence of carbon dioxide and temperature depended on the relative magnitudes of the two factors. Differences in oxygen concentration and pH were less important. Shelford and Powers (1915) used the continuous gradient tank technique in the study of herring fry (Clupea pa l la s i Valenciennes) and showed that these f ish oriented to - 8 -gradients of dissolved gasses and temperature. Powers (1939), and Powers and Clark (1943), advanced the opinion that carbon dioxide gradients were important i n the orientation of adult salmon during t h e i r spawning migration. They believed that the intense metabolism of the f i s h p r i o r to spawning increased the concentration of . carbon dioxide i n t h e i r bodies and drove them to seek waters of low carbon dioxide content. Hasler and Wisby (1951) , presented data which indicated, that mature coho salmon were influenced i n t h e i r orientation by the organic content of water i n streams and r i v e r s which they encountered during t h e i r spawning migration. (4) Response to S a l i n i t y Gradients The importance of s a l i n i t y gradients as d i r e c t i v e agencies i n the migration of fishes depends, i n the l a s t analysis, on the presence of oriented responses directed i n some r e l a t i o n to these gradients. Evidence from both f i e l d and experimental studies suggests that responses of t h i s type to s a l i n i t y do occur i n several species. Much of the e a r l i e r work on t h i s subject has been ably reviewed by Fontaine and Koch (1950), who c i t e d the work of Jordan (1914) on adult A t l a n t i c salmon, of Rodgers (1939) on the stickleback (Gasterosteus aculeatus Linnaeus), and Heldt's i n v e s t i g a t i o n (1924) of l a r v a l European eels, as fi e l d . s t u d i e s i n d i c a t i n g that freshwater exerted an at t r a c t i o n f o r these species. White (1941), noted that anadromous eastern brook trout (Salvelinus- f o n t i n a l i s ( M i t c h i l l ) ) of the A t l a n t i c coast kept to inshore waters where s a l i n i t y tended to be low. They were absent from regions such as the Bay of Fundy where s a l i n i t y values remained high near the shores. Huntsman, i n a. series of papers (1945a, 1945b, 1948a, 1948b, 1950), recorded observations which indicated that the movements of A t l a n t i c salmon were influenced by s a l i n i t y . He noted (1945a), that A t l a n t i c salmon parr were commonly found i n the inner part of the Maragree estuary, Nova Scotia, where the waters tended to be fresh or brackish. They were rar e l y seen i n the outer, more saline areas of the estuary. In a l a t e r paper (1948b), he made the comment \"... with steep s a l i n i t y gradients they [ A t l a n t i c salmon moving towards t h e i r spawning groundsj tend to keep i n water of low s a l i n i t y ...\". Huntsman (1948b) stated that salmon moving into r i v e r s were found congregated at s a l i n i t y gradients or i n fresh water, and came to the conclusion that \" S a l i n i t y gradients appear to be the p r i n c i p a l f a c t o r f o r the o v e r a l l movement of the salmon riverward.\" However, t h i s statement was by his own admission, uncorroborated by experimental evidence. Some data are available on the influence of s a l i n i t y on the movements of P a c i f i c salmon i n the open ocean. Powers (1939), stated that \"...Tagging experiments i n Alaskan waters have shown that the sockeye salmon [0± nerka) migrates to the spawning grounds along the paths of fresh-saltwater gradients ...\" and that \"... movements \"in the sea are l a r g e l y d r i f t s - 10 -and at the same time the salmon are held, within the bounds of a fresh-saltwater gradient . Clemens (1951), remarked that sockeye salmon smolts, on reaching the Strai t of Georgia, Br i t i sh Columbia, tended to remain in the upper, less saline regions of the channel. ^ As a f i n a l reference to f i e ld studies Hora- (1952), inferred that the increasing inland penetration of a pelagic, marine species, Hilsa t o l i , into the Hooghly River, India, was related to the deeper penetration of seawater into that r iver system. The work of Chidester (1922), was', perhaps the f i r s t experimental study carried out to determine the responses of fishes to seawater. Using paral le l flows of water to test the reactions of the Pacific k i l l i f i s h , (Fundulus heteroclitus Linnaeus), which moves from seawater to fresh or brackish water during spawning, Chidester found that this species responded positively to seawater. He stated that current and temperature were more ..important than sa l in i ty in the orientation of these f i s h . However, this conclusion does \"not necessarily follow from the data which he presented. Doudoroff (193$), used a continuous gradient tank to study the responses of the k i l l i f i s h . He found no evidence of a stable orientation with respect to sa l in i ty , and his data indicated that temperature gradients were more important than sa l in i ty gradients in the orientation of this species. Several investigations have been carried out on the response of the European eel, a catadromous species, to variations in the seawater-freshwater content of their medium. - 11 -Sylvest (1931) was c i t e d by Fontaine and Koch (1950), as the f i r s t to show d e f i n i t e l y the a t t r a c t i o n of freshv/ater f o r e lvers. Sylvest was not, however, on the basis of his data, able to a t t r i b u t e the influence of freshwater to any s p e c i f i c f a c t o r such as oxygen content, pH, temperature, or s a l i n i t y . Fontaine and Callamand (1941), used an apparatus consisting of communicating tanks i n which salinity.,, oxygen content, and pH could be varied i n order to e s t a b l i s h whether or not there existed i n l a r v a l eels a tropism related to s a l i n i t y which was separate from that to current. They felt, that the l a t t e r was the most important single d i r e c t i v e agency i n the movement of elvers upstream. Their investigation showed that a strong p o s i t i v e response to freshwater existed even i n the face of r e l a t i v e l y large differences i n oxygen concentration, and pH. They concluded that the a t t r a c t i v e influence of freshwater was an important element i n the movements of elvers upriver. This conclusion was corroborated by Van Heusden (1943), who studied the reactions of elvers to currents of water varying i n s a l i n i t y . Experimental data on the response of P a c i f i c salmon f r y to s a l i n i t y gradients have been supplied by Shepard (194#), who used a technique s i m i l a r to that of Chidester (1922), and Van Heusden (1943). Shepard showed that chum salmon responded p o s i t i v e l y to sea water i n both the a l e v i n and free-swimming stages and that preference f o r seawater - 12 -increased with age. Small differences in the temperature of the alternate streams of water (2.5°C.) did not alter their responses significantly. Coho fry, on the other hand, avoided even dilute solutions of sea water. Shepard .determined that the apparent threshold level of seawater i discrimination lay between 1.97 and 3.26 ° /oo. During field studies at Port John, British Columbia, in 1955 Hoar (Personal communication), noted that chum fry moving downstream continued out to sea, whereas coho fry did not. This observation suggested a difference in the behaviour of the two species toward seawater. B. PHYSIOLOGICAL ASPECTS OF MIGRATION (1) Sensitivity of Fishes to Variations in Salt Content The ability of fishes to orient to gradients of salinity depends on their ability to detect the presence of such gradients. .:. Several investigations have shown that the;sensitivity of fishes to dissolved organic materials is'extremely high. Hasler (1954), using the technique of conditioned response, was able to train fish to respond to organic material at extremely low dilutions. Brett and MacKinnon (1952), noted that dilutions of 1: 1,000,000 were within the sensory range of certain minnows. In a latter paper Alderdice, Brett, Idler and Fagerlund (1954), estimated that a repellent in mammalian skin could be detected by adult coho and spring salmon, migrating upstream, at the extraordinarily low concentration of 1:80,000,000,000. It would appear that the a b i l i t y of fishes to detect some organic materials i s very high. Much the same capacity i s apparent with respect to inorganic materials. Fontaine and Koch (1950), cited the work of Krinner (1934), who demonstrated.that the European minnow, (Phoxinus laevis) , reacted to sodium chloride solutions at concentrations as low as 0.003 ° / o o . In the classic work of Bul l (1938), the conditioned response technique was used to test the a b i l i t y of seventeen species of marine teleosts to discriminate between seawater solutions of s l ight ly different concentrations. The most sensitive f i sh tested, the spotted goby (Gobius flavescens G i l l ) , could differentiate between solutions only 0.06 °/oo different in concentration, in the range 30 to 35 ^oo. The least sensitive f i sh could distinguish .between solutions di f fer ing only 0.45 ° / o o in concentration. Bul l concluded that differences in sa l in i ty have a high perceptual value to f i s h . Fontaine and Koch (1950), pointed out that i f the Weber-Fechner law * has general application, this a b i l i t y to distinguish between solutions nearly similar in concentration would be s t i l l greater at low concentrations. * S k log I constant where: S I k - sensation - stimulus - constant - u -It can be concluded that salmon probably have the sensory capacity to detect f a i r l y marked gradients of sa l in i ty . On the other hand, there are data supplied by Craigie (1926), which would seem to indicate that adult sockeye salmon are able to return to their spawning grounds without the use of olfactory organs. Craigie transected the olfactory nerves of one half of a sample of 519 f i sh tagged in Johnstone Stra i t , 125 miles away from the Fraser River system, B r i t i s h Columbia, and presumed to be headed towards i t . However, as Wisby and Hasler (1954)j pointed out, this conclusion was of doubtful value due to the design of the experiment. (2) Physiological Changes Prior to Migration It i s apparent that marked changes occur in the Atlantic and Pacific-salmons, and in the European eel prior to migration (Hoar 1953» Fontaine, Leloup, and Olivereau 1952). Among the changes seen in the parr-smolt transformation of the Atlantic salmon are the following; loss of body fat, change in type of fat present, increase in cholesterol-type compounds, increase in resistance to seawater, loss of body chlorides, deposition of gaunine in the scales, and increase in blood copper. A l l these changes tend to make the salmon smolts more s imilar to marine than to freshwater f i sh . Black (1951a), Fontaine (1948, 1951b), and Hoar (1953) suggest that these changes, especially those associated with osmotic balance, plqce the f ish in a stressed condition which is alleviated by movement into the more concentrated medium. - 15 -Black (1951b) emphasized the importance of ch o l e s t e r o l - f a t t y acid metabolism. The r a t i o of these two classes of compounds has been related to the physical imbibition of water; a high c h o l e s t e r o l - f a t t y acid r a t i o r e s u l t i n g i n increased imbibition of water* Evidence was cited i n d i c a t i n g that the weight of the spleen, an important source of cholesterol, decreased i n some anadroraous species. The mobilization of spleen cholesterol was believed to increase the r a t i o of th i s compound to f a t t y acids, and hence the imbibition of water by tissu e s . The decrease i n body f a t , already noted, would enhance t h i s e f f e c t . There i s also evidence that body f a t s change i n type from the saturated to the unsaturated v a r i e t y . The l a t t e r are f e l t to be more ef f e c t i v e i n water imbibition, possibly through the formation of \"water clouds\" at unsaturated linkages by hydrogen bonding. Increased water absorption r e s u l t i n g from these effects would be counteracted by movement into a more concentrated environment, absorbed water being drawn by osmosis. (3) Influence of Endocrine Function on Migration Many of the changes noted above may have t h e i r source i n the a c t i v i t y of the endocrine organs. Fontaine and Koch (1950) Fontaine (1951a), and Hoar (1953), have emphasized the importance of the neuro-endocrine complex i n the i n i t i a t i o n of migratory movements, although l i t t l e i s known, as yet, of the precise r o l e which hormones play i n metabolic regulation i n fis h e s . Hoar (1953) suggested that a photoperiodic e f f e c t might - 16 -be important i n i n i t i a t i n g migratory movements through i t s influence on the p i t u i t a r y , and hence on general hormone physiology. Both Hoar (1951), and Fontaine, Leloup, and Olivereau (1952), presented data suggesting that increased p i t u i t a r y metabolism produced a hypersecretion of thyrotrophic hormones from the anterior p i t u i t a r y , and that t h i s i n turn resulted i n a condition of hyperthyroidism. Fontaine, Leloup, and Olivereau (1952) showed by both c y t o l o g i c a l and r a d i o l o g i c a l methods that the a c t i v i t y of the thyroid gland, as expressed by the concentration of i t s products i n the blood, was at a higher l e v e l i n the A t l a n t i c salmon smolt than i n the parr. The e f f e c t s of an increase, i n the concentration of thyroid products are many-fold. Thyroid extracts have been shown by Hoar (1951b), to promote/the deposition of guanine i n the scales of the A t l a n t i c salmon. However the lack of effectiveness of thiourea i n i n h i b i t i n g t h i s \" s i l v e r i n g \" reaction indicated that the thyroid gland, while influencing guanine deposition, did not e n t i r e l y control i t . Fontaine (194#) indicated that thyroid a c t i v i t y was important i n the positive rheotropism displayed by elvers moving upriver from the sea. He also emphasized (1951a) the r e l a t i o n s h i p of thyroid a c t i v i t y to gonadal development, a f a c t o r thought to be i n f l u e n t i a l i n migration. Koch and Heuts (1942), provided data i n d i c a t i n g the importance of thyroid hormones i n the osmoregulation of the - 17 -stickelback. Administration of thyroid derivatives reduced the a b i l i t y of t h i s species to t o l e r a t e high s a l i n i t y . Carp injected with thyroxine also showed a lowered resistance to sea water (Fontaine 1943)* F i n a l l y , Hoar and B e l l (1950) , demonstrated that the thyroid glands of chum salmon f r y retained i n freshwater became hyperplastic; a condition i n d i c a t i n g greatly increased a c t i v i t y . It seems that the thyroid gland i s associated with osmotic control although i t s precise actions are not as yet known. Its influence on c h o l e s t e r o l - f a t t y a c i d metabolism might p r o f i t a b l y be studied. Hoar, MacKinnon, and Redlich (1952.), found that treatment of chum salmon f r y with thyroxine increased t h e i r a c t i v i t y , a f a c t o r which may be correlated with the high l e v e l of a c t i v i t y seen i n these f i s h p r i o r to, and during seaward migration. In a l a t e r paper, Hoar, Keenleyside, and Goodall (1955) showed that coho and sockeye yearlings treated with thyroxine were more active than untreated f i s h . They expressed the opinion that thyroid effects were of a general type, increasing the general a c t i v i t y of the species. It was postulated that i t s action lay i n s e n s i t i z a t i o n of the central nervous mechanisms to external s t i m u l i . In an e a r l i e r paper Hoarl-(1953)' &&d expressed the opinion that the action of the t h y r o i d gland might l i e i n a general lowering of threshold stimulation l e v e l . Without doubt th i s s e r i e s of investigations has shown that the a c t i v i t y of the thyroid gland has some influence on - 18 -the behaviour and metabolic conditions leading to migration. The action of the other endocrine glands may also be important i n migratory behaviour. It was previously suggested that the p i t u i t a r y gland through formation of thyrotrophic hormones might control thyroid function. More d i r e c t evidence of the importance of p i t u i t a r y action i s to be .-.seen i n the work of V i l t e r (1946)., who studied the \"halophobia\" exhibited by l a r v a l eels. V i l t e r compared the reactions of normal elvers to seawater with those of hypo.physectomized animals, and found that while 100 % of the control group l e f t a concentrated solu t i o n of sea water during the period of observation, only 30$ of the experimental elvers behaved i n t h i s way. He concluded that there was a di r e c t r e l a t i o n s h i p between t h i s pattern of behaviour and the function of the p i t u i t a r y gland. Some recent data on the function of the adrenal cortex of the A t l a n t i c salmon (Fontaine and Hatey, 1954), showed that the concentration of 17 - hydroxycorticosteroids i n the plasma varied i n d i f f e r e n t stages of development. The parr had a much lower blood c o r t i c o s t e r o i d l e v e l than the smolts, (19.6 umg per 100 cc. plasma as compared to 8*5.5 umg per 100 cc. plasma), while a similar, but much les s marked difference was found between adult salmon entering r i v e r s and those over the spawning grounds. The authors suggested that there might be a connection between high s t e r o i d content and a c t i v i t y . Additional effects might also be present; 17 -hydroxycorticosteroids lacking ketonic or al c o h o l i c oxygen atoms at the carbon-11 position are known to be active i n water and e l e c t r o l y t e balance, while those having these reactive groups on the carbon-11 p o s i t i o n are considered to function i n the control of carbohydrate metabolism. (West and Todd 1955). The data on the physiological aspects of migration present a picture which i s f a r from complete. However, i t i s evident that d e f i n i t e relationships exist between the physiological state of f i s h p r i o r to migration and t h e i r behaviour. The role of hormones i n the i n i t i a t i o n and control of migratory movements might p r o f i t a b l y be studied to a greater length. - 20 -MATERIALS AND METHODS Materials Three species of the genus OncXorynchus (the P a c i f i c salmon) were studied i n the investigation; (0. keta (Walbaum)), the chum salmon, (0^ gbrbuscha (Walbaum)), the pink salmon, and (0. kisutch (Walbaum)), the coho salmon. Of these the chum and pink salmon migrate to sea as f r y soon a f t e r hatching. Coho salmon tend to remain f o r at leas t one year i n fr e s h water, migrating seaward as smolts. Data on the size and sources of the f r y are recorded i n Table I. A l l measurements were made from the t i p of the nose to the fork of the t a i l . Two groups of chum and two groups of coho salmon were used i n the experiments. . Data on these are recorded separately. A l l stocks were maintained at the University of B r i t i s h Columbia hatchery during the in v e s t i g a t i o n . The three species can be r e a d i l y distinguished by differences i n body shape, structure of the anal f i n , d i s t r i b u t i o n and length of parr marks, and colour. There was no d i f f i c u l t y , therefore, i n maintaining single species experimental populations. Methods The purpose of the in v e s t i g a t i o n was to examine the behaviour of salmon f r y encountering sharp gradients of s a l i n i t y , i n order to determine whether or not the seaward TABLE I Data on experimental salmon Species Group Average Size Standard Deviation Source 0. keta (1) 3$..7mm (67 fry) 2.4mm Cultus Lake* 0. keta (2) 42.9mm (42 fry) 3.5mm Cultus Lake* 0. gorbuscha (1) 33.4mm (42 fry) 1.7mm Oyster River 0. kisutch \"(1) 34.7mm (74 f r y ) 2.3mm Cultus Lake* 0. kisutch (2) 57.4mm (50 f r y ) 6.5mm Salmon River * F i s h reared from eggs i n the University of B r i t i s h Columbia hatchery. - 22 -movements of f r y are influenced by t h i s f a c t o r . Two assumptions were made i n the study; that the response of the f r y was a true expression of an innate behaviour pattern, uncomplicated by reactions to other variables, and that the behaviour of the sample represented the behaviour of the species as a whole. Ba s i c a l l y , the method consisted of of f e r i n g f r y the choice of remaining i n freshwater or moving into seawater. The responses of f r y to d i f f e r e n t concentrations of seawater were studied by t h i s means, and the e f f e c t of p r i o r acclimation to seawater on t h e i r responses determined. It was also possible to determine, by an i n d i r e c t method, the a c t i v i t y of the f i s h under d i f f e r e n t conditions. Apparatus Experiments were conducted i n two wooden troughs each, made up of three tanks measuring 60 x 30 x IS cm. These tanks were divided into compartments of equal volume by central p a r t i t i o n s 23 cm. high (Figs. 1 and 2 ) . The troughs were painted throughout with \"Rustoleum\", a nonr-toxic. paint, which protected the material of the troughs and provided a uniform v i s u a l background f o r the f i s h . Temperature was maintained by means of a water bath with a continuous flow of water at the same temperature as that i n the stock troughs. Some warming occurred i n the upper few centimetres of the water i n the troughs, but temperature p r o f i l e s taken i n adjacent compartments were L O N G I T U D I N A L S E C T I O N ® A F I CL \"FRESH WATER BRIDGE\" ® O U T F L O W PIPE © INFLOW PIPE ® COOLING BATH ® PARTITION C R O S S S E C T I O N 0 O B S E R V A T I O N M IRRORS $ L IGHT S O U R C E <3> AIR S U P P L Y ® S A M P L I N G S I P H O N <8) F R E S H WATER S O U R C E FOR \" B R I D G E \" ® E X P E R I M E N T A L T A N K ® C O O L I N G B A T H Fig.2. Diagram of apparatus - 25 -e s s e n t i a l l y uniform (Fig. 3). The temperature of the water varied from 5.0°C. to 11.5°C. during the course of the experiments. Light was supplied by Westinghouse 60 Watt \"Lumiline\" bulbs mounted i n a r e f l e c t o r i n front of the apparatus. Inclined mirrors r e f l e c t e d the l i g h t downward onto the tops of the troughs. This arrangement reduced surface heating and allowed observation of the f i s h . The i n t e n s i t y of the l i g h t was maintained at 1.17-0.11 foot-candles (measured at the water surface) and was approximately that which might be expected over streams during the l a t e evening when downstream movement occurs. The use of mirrors produced some shadowing i n the troughs. The effects seemed to be minor, and were s i m i l a r i n each tank. It i s u n l i k e l y that they produced any niajor change i n the reactions of the f i s h . The concentrations of dissolved gasses i n the freshwater and seawater solutions were kept approximately equal by aerating each compartment p r i o r to observation. The currents set up by the bubble streams were us e f u l i n preventing thermal s t r a t i f i c a t i o n i n the tanks before observations were begun, but they were turned o f f at the s t a r t of each experiment i n order to decrease the rate of exchange of water between compartments (Fig. 4)• Differences i n the concentration of gasses i n seawater and freshwater solutions were unavoidable due to differences i n s o l u b i l i t y c o e f f i c i e n t s i n the two solutions. However, -26-8 0 9 0 10.0 11.0 8 0 9.0 10.0 ll 0 T E M P E R A T U R E - C * Pig.3- Typical temperature p r o f i l e . 7 .0 0 £ 5 5 0 75 100 125 i«>0 175 2 0 0 2 2 5 2t>0 T I M E Pig.k. Rise i n s a l i n i t y of freshwater compartments. - 27 -analyes of the oxygen content of the water i n the compartments made during most of the experiments indicated that the differences were s l i g h t , and they probably did not ef f e c t the behaviour of the f i s h . The average concentration of oxygen i n a l l the seawater solutions tested was 9.43* 0.12 mg. oxygen per l i t r e , while that i n fresh water was 11.17*0.32 mg. oxygen per l i t r e . No analyses of carbon dioxide concentrations were made. The water samples used i n oxygen and s a l i n i t y analyses were drawn from the central portion of each compartment by means of permanently fi x e d siphons. The operation of these siphons did not appear to disturb the f i s h . Iii order to allow the f r y to move between compartments a \"freshwater bridge\" two centimetres high was created over the p a r t i t i o n s . This was done by running freshwater from the main water supply slowly into the A, D, and E compartments u n t i l the desired height was reached. A certain amount of exchange between freshwater and saltwater could not be avoided (Fig. 5). Freshwater moving into the seawater had a tendency to mix by entrainment. This freshwater-saltwater mixture, while l i g h t e r than the main body of seawater had a density greater than freshwater, and flowed over the p a r t i t i o n s mixing into and r a i s i n g the s a l t concentration of the freshwater. Some further exchange occurred due to physical processes and the a c t i v i t y of the f r y following t h i s i n i t i a l mixing. S a l i n i t y p r o f i l e s were taken to determine whether or not v e r t i c a l gradients were present which might influence the - 28 -orientation of the f r y . A t y p i c a l p r o f i l e , ( F i g . 6), showed that the s a l i n i t y d i s t r i b u t i o n i n the freshwater compartment was e s s e n t i a l l y uniform. Marked s t r a t i f i c a t i o n , however, occurred i n the seawater compartments. This had l i t t l e influence on the responses of the pink and chum f r y , but affected the movements of the coho f r y . The apparatus, based on one used by Berta Baggerman i n Professor G.P. Baerends laboratory at the University of Gronigen, Netherlands, was e s s e n t i a l l y a sharp gradient tank i n which the gradient was maintained by the e f f e c t of the .central p a r t i t i o n . In contrast to one used by Shepard (1948) f o r the same general purpose, i t avoided the use of flowing water and the attendant complication of the reaction of the f r y to currents and to small differences i n temperature and strength of alternate currents. This apparatus i s also believed to be an improvement over that described by Shelford and Powers (1915) because of the r e l a t i v e sharpness of the gradients which could be maintained. Test Solutions Seawater used i n the experiments during the early part of„ the, summer was obtained from English Bay, Vancouver, B.C. and during the l a t t e r part of the summer from the Great Northern Cannery, West Vancouver, B.C. It was transported to'the University i n 50 l i t r e glass carboys and was never kept longer than one week before use. -29-0.36 V 0 . 3 6 / 0.34 0.39 0.39 037 ^ / I 0.41 045 0.41 665 6.62 6.16^ \\ / 757 7.53 7.66 LONGITUDINAL SECTION OF EXPT 'L TANK I O-POSITION OF INFLOW TUBE Fig.f?. I n i t i a l water exchange between compartments, , ISOTONIC REGION 1.28 1.29 '//. 2.27 1.79 1.75 10.44 10.14 1026 FRESH WATER REGION HYPERTONIC REGION 1.28 12.27 12.46 12.36 LONGITUDINAL SECTION OF E X P T ' L TANK Fig.6. Typical s a l i n i t y p r o f i l e at 200 minutes. - 30 -Chemical Methods Seawater concentrations were determined by the Mohr t i t r a t i o n f o r t o t a l chloride with s i l v e r n i t r a t e , The use of dextrin curcumvented the necessity of prolonged shaking during the t i t r a t i o n . D i c h l o r o f l o r o s c e i n was used as an indicator, as i t s end point was f e l t to be more sharply defined than that of the standard potassium dichromate indicator., A l l concentrations were recorded as s a l i n i t y values. The unmodified Winkler t i t r a t i o n was used i n the determination of the dissolved oxygen content of freshwater and seawater solutions. Measurements of the t o t a l dissolved material I n the water were made i n several instances by means of a dipping refractometre. Procedure The same procedure was followed i n a l l experiments. The A,. D, and E compartments, (Fig. 1), were f i l l e d to the l e v e l of the p a r t i t i o n s with freshwater and the remaining compartments were f i l l e d with t e s t solutions. In control experiments freshwater was placed i n a l l compartments. Care was taken not to allow water to come int o contact with the skin. Brett and MacKinnon (1952), and Alderdice, Brett, Idler, and Fagerlund (1954), have shown that adult coho and spring salmon react negatively to water containing traces of a compound, possibly a polypeptide, present i n - 31 -mammalian skin. Although there was no evidence that fry-react i n t h i s manner the precaution was f e l t to be a v a l i d one. Samples of eight to twelve f i s h were placed i n the freshwater compartment of each tank. Larger groups (14-20 fry) had a tendency to swim a c t i v e l y back and f o r t h across the \"bridge\" without moving into e i t h e r compartment. Much the same d i f f i c u l t y was encountered by Shepa.nd\"1. (194$) i n his i n v e s t i g a t i o n . Reduction i n the sample si z e removed t h i s \"group-activity\" f a c t o r and allowed the expression of preference reactions. The f i s h were l e f t i n freshwater f o r a s i x to eight hour period of acclimation. There i s some physiological basis f o r the length of the acclimation period. Black (1954, 1955) found a marked increase i n the l a c t i c acid l e v e l of exercised y e a r l i n g Kamloops trout (Salmo g a i r d n e r i i kamloops Jordan). The same condition was noted i n f i s h removed b r i e f l y from water. In these experiments the f r y were disturbed as l i t t l e as possible during the transfer from stock tanks to apparatus, and i t was f e l t that a period of s i x to eight hours would be s u f f i c i e n t to ensure a return to t h e i r p h y s i o l o g i c a l l y normal state. Following the period of acclimation, freshwater was run into the tanks, as described above, and the \"freshwater bridge\" established. The number pf f i s h i n each compartment was recorded at two minute i n t e r v a l s f o r ten minute periods beginning at 0, 10, 25, 45, 75, 105, 165, 195, and i n the - 32 -case of the pink salmon 225 minutes a f t e r the \"bridge\" was completed. A l l observations were made during the evening. Several authors, (MacKinnon and Brett 1954, Neave 1954), have shown that downstream movement of migrant f r y occurs at night and reaches i t s peak near midnight. The period of observation i n these experiments was chosen to coincide as much as possible with the normal period of maximum a c t i v i t y of the f i s h . Studies Carried Out The responses of the three species of f r y and of coho i n the process of parr-smolt transformation to i s o t o n i c and hypertonic solutions of seawater were investigated. During the course of these studies control experiments, i n which freshwater was placed i n both compartments provided a basis f o r comparison. An additional ser i e s of experiments was c a r r i e d out on chum f r y to determine the e f f e c t of previous acclimation to seawater on the responses to seawater. In these experiments the f r y were acclimated to e i t h e r i s o t o n i c or hypertonic seawater f o r twenty-four hours p r i o r to observation. Following t h i s , they were placed i n freshwater f o r the s i x to eight hour acclimatory phase of the experiments before having the opportunity to respond to seawater. Acclimation was carried out i n glass battery jars having a capacity of approximately 9 l i t r e s . Twenty-five to t h i r t y - 33 -f r y were placed i n each j a r . The water was aerated, and the temperature of the solutions i n the jars was the same as that i n the holding troughs. Analysis- of Data (1) Average Response The s i x i n d i v i d u a l values recorded i n each tank at each period of observation were averaged, and the means of the pooled averages f o r a l l r e p l i c a t i o n s i n each set ,of experiments were analyzed. Comparison of the r e l a t i v e numbers of f i s h i n freshwater with the number i n seawater was considered as the \"average response\" of the f r y . The chi-square test, (Snedecor 1946), was used to measure the departure from uniform d i s t r i b u t i o n between the freshwater and saltwater compartments. In i t s e l f , t h i s method of analysis does not \"prove\" anything about the d i s t r i b u t i o n of the f i s h . It does, however, give a basis on which a statement concerning the p r o b a b i l i t y of observed d i s t r i b u t i o n s can be made. For instance, i n these experiments chi-square values above 3 . $4.indicated a s i g n i f i c a n t departure from uniformity at the 5 % l e v e l , i e . such a r e s u l t would occur by chance only 5 times out of 100. S i m i l a r l y , a computed chi-square value greater than 6.63 indicated that i n only one case out of one hundred would the observed d i s t r i b u t i o n be found by chance i n sampling from a uniform d i s t r i b u t i o n . Larger values indicate even l e s s p r o b a b i l i t y - 34 -that the d i s t r i b u t i o n concerned had occurred by chance. Since the number of f r y tested i n the d i f f e r e n t sets of experiments varied, chi-square values of both the means mentioned above, (raw data), and percentage values of the means (°/o data), were calculated. This procedure was used to obtain the values recorded on the graphs. The difference i n the \"average response\" of the f r y under d i f f e r e n t conditions were made more r e a d i l y comparable by t h i s means since the chi-square values were then calculated on equal samples. The use of percentage data was j u s t i f i e d only i n cases where the sample of f r y exceeded 100 individuals and lead to some loss i n the weight of the resultant values. It i s emphasized that t h i s procedure was only undertaken i n order that graphical comparisons of the responses of equal samples of f r y might be presented. Chi-square values of both raw data and percentages data are recorded i n the appendix. The only exception to t h i s method of presentation occurred i n the investigation of the response of the pink salmon f r y . In t h i s case one of the three samples of f r y used numbered le s s than 100 f i s h , and the values on the graph i l l u s t r a t i n g t h e i r responses are calculated on the basis of the raw data. These curves are not therefore, s t r i c t l y comparable with those i n d i c a t i n g the responses of the chum and coho f r y . Chi-square values were plotted against time to show the i n t e n s i t y of the response at any one time, and the change i n response with time. Values l y i n g below the time axis indicate - 35 -concentration i n freshwater, those above the axis concentration i n saltwater. In the control' experiments, where both compartments contained freshwater, the values below the time axis referred to concentration i n the compartment i n which the f i s h were o r i g i n a l l y placed (\"freshwater compartment\"), and those above the l i n e indicate concentration i n the alternate compartment (\"saltwater compartment\"). In some experiments not a l l of the chi-square values were s i g n i f i c a n t . In these cases, the sum of the values was taken and compared against the chi-square l e v e l f o r the appropriate number of degrees of freedom, a procedure described by Snedecor (1946). (2) Comparison of the \"Average Response\" i n D i f f e r e n t Sets of Data The \"average responses\" to d i f f e r e n t strengths of seawater and following d i f f e r e n t treatments were compared to determine whether or not s i g n i f i c a n t differences i n response had occurred. A modified chi-square test f o r the simultaneous treatment of two sets of data was u t i l i z e d f o r t h i s analysis {Snedecor 1946). (3) A c t i v i t y A measure of the a c t i v i t y of the f i s h was made by determining the average difference i n the number of f i s h i n each compartment at successive two minute i n t e r v a l s . These - 36 -values are minimum measurements due to the p r o b a b i l i t y of multiple exchanges between the compartments. Nevertheless, the values obtained were useful i n i n d i c a t i n g gross changes i n the a c t i v i t y of the f i s h under d i f f e r e n t conditions. (4) Homogeneity Tests B a r t l e t t ' s test f o r homogeneity of variance (Snedecor 1946) was applied to f i v e sets of data, chosen at random, to determine whether the results of any one tank varied s i g n i f i c a n t l y from those from the remainder of the tanks. Data i n Appendix The following data are tabled i n the appendix: (1) Chi-square values based on \"raw data\" and \" % data\". (2) Chi-square values f o r comparisons of response under different.conditions and treatments. (3) A c t i v i t y . (4) Homogeneity of variance t e s t s . - 37 -RESULTS CHUM SALMON FRY Data regarding the siz e and number of f r y used i n each series of experiments, number of re p l i c a t i o n s , and the average s a l i n i t i e s of experimental and accliraatbry solutions are recorded i n Table I I . A. Observations on Behaviour Some qu a l i t a t i v e observations were made on the behaviour of the f r y . During the period of acclimation, while the f r y were i n the freshwater compartments, they usually swam about a c t i v e l y throughout the whole water mass or oriented themselves to the flow produced by the aerators. Nipping was rarely noted and was not a c h a r a c t e r i s t i c pattern of behaviour. While freshwater was being run into the A, D, and E compartments (Fig.2) to produce the \"freshwater bridge\" the f r y occasionally formed loose, r e l a t i v e l y inactive groups near corners and close to the bottoms of t h e i r compartments. They showed no preference f o r any p a r t i c u l a r areas. More often, they oriented to the incoming flow of water. When flooding was complete the f r y had a tendency to school and swim rapidly back and f o r t h across the \"bridge layer\". Individuals occasionally dove f o r b r i e f i n t e r v a l s into the main water mass of either compartment. This period, termed the \"exploratory phase\", lasted f o r about one h a l f TABLE II. Chum salmon f r y experiments Series Average size of f r y Sample Size Mo. r e p l i c a t i o n s Ave.salinity at 200 min. S a l i n i t y of acclimation s o l T n f .w. S .Wi ••. Control 38.7 mm (2.4)-, 184 . 18 Isotonic t t 181 18 6.43* 5.10 Hypertonic I t 182 18 1.01 19.43 Isotonic Acclimated to hypertonic 42.9 mm (3.5) 138 18 0.69 6.02 22.22 Hypertonic Acclimated t6 isotonic » 153 17 1.32 23.69 9.23 Hypertonic Acclimated to hypertonic t t 245 2£ 1.26 22.99 22.54 * A l l s a l i n i t y values i n these tables are i n parts per thousand (6/ 0 0) ** Bracketted figures r e f e r to standard deviations of the mean. - 39 -hour, a f t e r which the aggregations slowly broke up and the f r y began to express t h e i r reactions as individuals rather than as a group. This phase was termed the ^ i n d i v i d u a l response phase\". B. Control Experiments The f r y tended to remain i n the compartments into which they had been o r i g i n a l l y placed (Fig.7 ) . Although thi s tendency decreased somewhat with time, no fewer than 67$ of the f r y were recorded i n the A, D, and E compartments during any one period of observation. The lowest chi-square values exceeded the 99.5% l e v e l of significance, and t h i s , together with the general constancy of the d i s t r i b u t i o n indicated a very small p r o b a b i l i t y that the d i s t r i b u t i o n had occurred by chance. It i s evident that some fact o r must have been operating to increase the a t t r a c t i o n of these compartments f o r the f r y . C. Reactions of Unacclimated Fry to Sea Water (1) Response to Isotonic Sea Water The data on the response of the f r y to isotonic seawater are summarized i n F i g . 7. I t i s evident that the f r y responded r a p i d l y and p o s i t i v e l y to the seawater stimulus, and that t h e i r response increased s t e a d i l y with time. At the end of the experiment 82$ of the f r y were found i n the seawater compartments. Comparison -of these data with those Pig.7« Response of unacclimated chum salmon f r y to sea water. - 41 -on the d i s t r i b u t i o n of f i s h i n the control experiments indicated a s i g n i f i c a n t difference i n d i s t r i b u t i o n at a l l times a f t e r f i f t e e n minutes. The response of the f r y to isotonic seawater was c l e a r l y p o s i t i v e even i n the face of the a t t r a c t i o n of o r i g i n a l compartments noted i n the control experiments. (2) Response to Hypertonic Seawater The response of f r y to hypertonic seawater was i n i t i a l l y more marked than that to isotonic seawater (Fig. 7 ) . The maximum response was reached at 80 minutes when $9 .9$ of the fr y were observed i n seawater. Thereafter, the response decreased s l i g h t l y , and at the end of the experiment 76 .9$ were i n seawater. Comparison of the average percentages of f r y i n the two seawater solutions during the f i r s t minutes of the experiment showed that the f r y responded more rapidl y to hypertonic seawater than to iso t o n i c seawater (Tables V and VII). Comparison of these data with those on the : d i s t r i b u t i o n of the f r y i n the control experiments showed that there was a s i g n i f i c a n t concentration of the f r y i n seawater at a l l times (Table V I ) . The response to hypertonic seawater, therefore, was d e f i n i t e l y positive.';. A s i g n i f i c a n t difference between responses to isoton i c and hypertonic seawater was apparent during the f i r s t 140 minutes of observation. Afte r t h i s time, there was no s i g n i f i c a n t difference i n the number of f r y i n the two solutions. - 42 -D. E f f e c t s of Acclimation to Seawater on Response to Seawater (1) Response to Isotonic Seawater Following Acclimation to Hypertonic Seawater. The response of acclimated f r y to isotonic seawater was more, rapid than that of unacclimated f r y , as can be seen by comparison of the percentages of f r y i n seawater during the f i r s t periods of observation (Table V). . Although most of the i n d i v i d u a l chi-square values did not exceed the c r i t i c a l l e v e l f o r 95$ s i g n i f i c a n c e , (Fig. 8), a comparison of the d i s t r i b u t i o n of these'fry with'that of the control f r y indicated that there was a s i g n i f i c a n t difference i n d i s t r i b u t i o n at a l l times a f t e r the f i r s t observation (Table VI). In a l l cases the chi-square values f o r t h i s comparison exceeded the c r i t i c a l l e v e l f o r 95% significance, and i n a l l but one case (15 minutes) also exceeded that f o r 99.5$ s i g n i f i c a n c e . The response of f r y to i s o t o n i c seawater was therefore s t i l l p o s i t i v e following acclimation. A s i m i l a r comparison of the d i s t r i b u t i o n of these f r y with that of non-acclimated f r y responding to isotonic seawater revealed a s i g n i f i c a n t difference i n response a f t e r 30 minutes (Table VI). Analysis revealed that there, was less than one chance i n two hundred that t h i s difference i n d i s t r i b u t i o n had occurred by chance. (2) Response to Hypertonic Seawater following Acclimation to Isotonic Seawater. The results of these experiments are shown i n F i g . 9. The chi-square values obtained were at a l l times a f t e r the \\ Pig.8. Response of chum salmon f r y to i s o t o n i c sea water following acclimation to hypertonic sea water. — 44 \" f i r s t two observations well above the 99.5$ l e v e l of sign i f i c a n c e , (Table V I I ) . Comparison the these data with those on the f r y i n the control experiments showed that there was a s i g n i f i c a n t difference i n d i s t r i b u t i o n at a l l times (Table VIII A). In the l a t t e r case, a l l chi-square values were well above the 99.5$ l e v e l . There was no doubt that the response of the f r y to hypertonic seawater i s pos i t i v e even a f t e r acclimation. The response of these f r y d i f f e r e d somewhat from that of unacclimated f r y i n that there was no intermediate maximum response. Comparison of the two sets of data showed that the response of unacclimated f r y was s i g n i f i c a n t l y greater at 50, 80, 110, and 140 minutes (Table VIII B). During these periods the chi-square values of the comparison exceeded the 99.5$ l e v e l . At 05, 15, 30, 170, and 200 minutes there was no si g n i f i c a n t d i f f e r e n c e . Thus the acclimated f r y did not respond to seawater more quickly than the unacclimated f r y , nor was there any s i g n i f i c a n t difference i n the l e v e l of the f i n a l response. Some e f f e c t on the intermediate stages of t h e i r response was apparent. (3) Response to Hypertonic Seawater Following Acclimation to Hypertonic Seawater. The f r y responded rapid l y and p o s i t i v e l y to seawater as shown i n F i g . 9. At a l l times a f t e r f i f t e e n minutes, the chi-square values exceeded the 99.5$ s i g n i f i c a n c e l e v e l (Table V I I ) . The concentration .of f r y i n seawater increased s t e a d i l y u n t i l the end of the experiments, and there was no 70 60 00 ro i Pig.9 . Response of chum salmon f r y to hypertonic sea water following acclimation. - 46 -intermediate peak response. Comparison of data on the d i s t r i b u t i o n of these f r y with that of f r y under d i f f e r e n t conditions of treatment (Tables VIII A and VIII B) indicated the following:. (a) At a l l times there was a s i g n i f i c a n t difference between the d i s t r i b u t i o n of control f r y and these f r y . (b) A s i g n i f i c a n t difference between the responses of acclimated and non-acclimated f r y from 80 to 200 minutes was indicated by the summation of chi-square values. (c) There was no s i g n i f i c a n t difference between the responses of f r y acclimated to isoton i c seawater,. and those acclimated to hypertonic seawater. The conclusion can be drawn that f r y respond p o s i t i v e l y to hypertonic seawater a f t e r p r i o r experience i n seawater, and that there i s a difference i n the f i n a l l e v e l of response. E. A c t i v i t y (1) Unacclimated Fry A c t i v i t y can be correlated with the two phases of behaviour previously noted; the \"group exploratory phase\", and the \" i n d i v i d u a l preference phase\" ( F i g . 10). During the f i r s t period, the a c t i v i t y of f r y exposed to seawater at both isoto n i c and hypertonic concentrations was greater than that of f r y i n freshwater (control experiments). The f r y reacting to isotonic seawater exhibited a greater a c t i v i t y than those faced with hypertonic seawater during the \"exploratory phase\". -47-- 48 -In the second phase the s i t u a t i o n was reversed. The a c t i v i t y of the f r y i n the hypertonic solu t i o n reached a minimum l e v e l at 80 minutes and increased slowly a f t e r t h i s point. The f r y faced with the iso t o n i c solution, on the other hand, showed a steady decrease i n a c t i v i t y with time u n t i l the end of the experiments. A d i r e c t r e l a t i o n s h i p between a c t i v i t y and response was apparent during the i n i t i a l 110 minutes of the experiments. (Fig. 11). This c o r r e l a t i o n was not as noticable during the l a t t e r part of the experiments, or at any time i n the control experiments. The slope of the activity-response curve was negative, i n d i c a t i n g increased response as a c t i v i t y decreased. (2) Acclimated Fry A c t i v i t y of f r y responding to seawater under d i f f e r e n t conditions of acclimation i s summarized i n F i g . 12. A c t i v i t y of the f r y i n freshwater (control experiments) was added f o r comparative purposes. These data show the same type of time rel a t i o n s h i p as did those f o r non-acclimated f r y ; an i n i t i a l period of r e l a t i v e l y high a c t i v i t y related to \"group exploratory a c t i v i t y \" , and a following period of decreased a c t i v i t y during which the i n d i v i d u a l responses of the f r y occurred. The acclimated f r y , however, d i f f e r e d from the non-acclimated f r y i n that they tended to be as active, or more.active, than the control f i s h during the second phase of a c t i v i t y . The reverse s i t u a t i o n held i n unacclimated f r y can be seen by a comparison of average a c t i v i t i e s during the two TO 60 50 40 SO CO 10 O 10 20 90 40 50 60 70 (-) CHI SOUARC V A L U r S (4) Figjj... Activity-respgnse relationship in unacclimated chu^sahnon fry. -50-A CONTROL • ISOTONIC,ACCLIMATED TO HYPERTONIC • HYPERTONIC,ACCLIMATED TO ISOTONIC O HYPERTONIC,ACCLIMATED TO HYPERTONIC 0 9 19 5 0 9 0 Pig.12. A c t i v i t y of acclimated chum salmon f r y . - 51 -phases (Tables XV and XVI). The r e l a t i o n s h i p between a c t i v i t y and response i s shown i n F i g . 13. This r e l a t i o n s h i p i s more or les s d i r e c t during the i n i t i a l part of the experiments, although i n no case i s i t as sharp as that seen i n the non-acclimated f r y . The slopes of the curves tend to be negative, i n d i c a t i n g decreasing a c t i v i t y with increasing response. The lack of c l a r i t y i n t h i s r e l a t i o n s h i p , together with the greater a c t i v i t y of the f r y indicated that they were more independent of the medium than were non-acclimated f r y . PINK SALMON FRY Data regarding the siz e and number of f r y used i n each experiment, number of re p l i c a t i o n s , and the average s a l i n i t i e s of the experimental solutions are shown i n Table I I I . A. Observations on Behaviour Qualitative observations on the pink salmon f r y were much the same as those i n the chum f r y . The same patterns of orientation were noted p r i o r to the establishment of the \"fresh water bridge\", and again nipping was not c h a r a c t e r i s t i c . Following the creation of the \"bridge\" the f r y schooled and swam back and fo r t h across the \"bridge layer\", and occasionally dove into the main water mass of e i t h e r compartment. A d i v i s i o n of t h e i r response into \"exploratory\" and 'Individual preference\" was not as apparent as i n the case of the chums. Possibly t h i s was because they remained 10.0 9.0 x ao CO ui 0. CO t-u Z Ui > o TO 60 SO 4.0 oe hi > ° so CO (0 o OB an U 10 UI > O ISOTONIC,ACCLIMATED TO HYPERTONIC A HYPERTONIC, ACCLIMATED TO ISOTONIC • HYP E RTONIC,ACCLIMATED TO HYPERTONIC 40 SO 2 0 10 0 10 CHI SQUARE VALUES i vn i CO so (4) Fig, 13» Activity-response relationship in acclimated chum saloon fry. TABLE I I I Pink salmon f r y experiments Series Ave. Size of f r y Sample s i z e No. r e p l i c a t i o n s Ave. s a l i n i t y at 200 min. Control 33.4 mm (1.7) * 107 11 Fresh water Sea water Isotonic n 140 14 0.57 (0121) 8.27 (0.03) Hypertonic tt 84 10 0.66 (0.25) 20.34 (0.65) * Bracketted figures r e f e r to standard deviations of the mean. - 54 -r e l a t i v e l y more active throughout the period of observation. (Fig.15)• Hoar (personal communication) believed that pink f r y were more \"nervous\" f i s h than chum f r y and they may have a lower threshold of stimulation., which prevented as marked an expression of preference as was seen i n chum f r y . B. Control Experiments The f r y remained i n t h e i r o r i g i n a l compartments during the f i r s t h a l f of the experiments (Fig. 14) • A f t e r t h i s , they moved a c t i v e l y into the alternate compartments, and a more or less uniform d i s t r i b u t i o n was recorded. Most of the chi-square values indicated a tendency f o r concentration i n the o r i g i n a l compartments although the summation of these values did not exceed the c r i t i c a l l e v e l at 95$ s i g n i f i c a n c e (Table IX). This tendency however may be just as r e a l as that seen i n chum f r y , although the greater a c t i v i t y of these f i s h may have prevented i t s expression to as great an extent. The sum of the chi-square values was somewhat greater than the c r i t i c a l value f o r 70$ significance.. Thus there was a pro b a b i l i t y of t h i s d i s t r i b u t i o n occurring by chance s l i g h t l y less than three out of seven times. C. Reactions of Fry to Seawater (1) Response to Isotonic Seawater. The f r y responded slowly to isoton i c seawater (Fig.14) and the f i r s t d i s t r i b u t i o n s i g n i f i c a n t l y d i f f e r e n t , from that F i g . l J i . Response of pink salmon f r y to sea water - 56 -of the control f r y (at the 95$ l e v e l ) was not recorded u n t i l 110 minutes. Chi-square values f o r comparison did not exceed the c r i t i c a l l e v e l i n a l l cases, although summation indicated a s i g n i f i c a n t difference i n d i s t r i b u t i o n at a l e v e l greater than the 99 .5$ (Table X). The response may be considered pos i t i v e , although le s s intense than that shown by chum f r y under the same conditions. This may have been due to t h e i r higher l e v e l of a c t i v i t y . (2) Response to Hypertonic Seawater The response to hypertonic seawater was slower than that to isotonic seawater, (Fig.14) but comparison of the d i s t r i b u t i o n of these f r y with those of the control f r y revealed a clear-cut p o s i t i v e response to hypertonic seawater at a l l times a f t e r 80 minutes (Table X). Direct comparison with the d i s t r i b u t i o n of f r y responding to i s o t o n i c seawater did not always reveal a s i g n i f i c a n t difference on response (Table X). However, the sum of chi-square values a f t e r 110 minutes (the f i r s t time at which the percentage of f r y i n hypertonic seawater was greater than that of f r y i n isotonic seawater) exceeded the 99 .5$ l e v e l , suggesting a s i g n i f i c a n t difference i n response of the f r y to the two solutions. D. A c t i v i t y The data on the a c t i v i t y of the f r y i n freshwater and seawater solutions (FJLg.15) showed that i n each case a c t i v i t y increased from an i n i t i a l low l e v e l to a maximum value and then decreased slowly. - 5 7 -Fig . l 5 . A c t i v i t y of pink salmon f r y I - 58 -There was l i t t l e difference i n the a c t i v i t y l e v e l s of the f r y i n freshwater (control experiments) and i n isotonic seawater. The a c t i v i t y of the control f r y was somewhat greater than that of the f r y i n isotonic s o l u t i o n during the f i r s t 30 minutes of the experiments, but l e s s i n the l a s t 90 minutes. The a c t i v i t y of the f r y i n hypertonic solutions was much les s at a l l times. It was mentioned e a r l i e r , that the comparatively less intense responses of the pink f r y might be. due to t h e i r greater \"nervousness\" i e . lower threshold of stimulation to a c t i v i t y . This i s bornoouttby a comparison of the average a c t i v i t i e s of pink and chum f r y during the \"exploratory\" and \" i n d i v i d u a l preference\" phases of the control experiments (Tables XV and XVII). These data indicate that a c t i v i t y i s a factor which must be considered when comparing the responses of these two species to seawater under s i m i l a r experimental conditions. An attempt to correlate a c t i v i t y and response was made (Fig.16). A f a i r l y d i r e c t r e l a t i o n s h i p was apparent i n the a c t i v i t y and response of the f r y fac i n g hypertonic seawater, but much less marked i n the other two groups. It i s puzzling to note that maximum response and maximum a c t i v i t y both occurred at 140 minutes i n hypertonic seawater, and that i n general, the slopes of the a c t i v i t y -response curves are p o s i t i v e . This rela t i o n s h i p , which i s the reverse of that found i n the chum f r y , may be related i n some way to the greater a c t i v i t y of pink salmon f r y . Fig.16. Activity-response relationship in pink salmon fry. - 6 0 -G0H0 SALMON FRY AND SMOLTS Data on the size and number of f r y and smolts used i n each series of experiments, the number of r e p l i c a t i o n s , and the average s a l i n i t i e s of t e s t solutions are recorded i n Table IV. FRY A. Observations on Behaviour During the acclimation period the f r y were r e l a t i v e l y inactive, resting on or near the bottom, or swimming slowly i n the lower regions of t h e i r compartments. Swimming f i s h were observed to orient to the currents provided by the aerators. Nipping seemed to be more prevalent among the coho f r y than among chum or pink f r y , but no quantitative measurements were made. During the establishment of the \"freshwater bridge\" the f i s h usually formed loose, i n a c t i v e groups near the bottom or walls f o r a short time. In other cases the f r y oriented to the inflowing water. Following completion.of the bridge the f r y i n control and isotonic experiments behaved much as had pink and chum f r y under s i m i l a r conditions, moving back and f o r t h across the bridge layer and occasionally diving into the water of eithe r compartment. Coho f r y facing hypertonic seawater were observed to dive frequently, into freshwater compartments, and l e s s often into seawater compartments. TABLE IV Coho salmon fry and sraolt experiments f Series Ave. size of fry Sample size No. replications Ave. salinity at 200 min. Fresh water Sea water Control Isotonic Hypertonic 34.7 mm (2.3) t! tt 206 170 180 21 18 18 0.74 %>o 1.42 %o 7.31 °/oo 23.96%o Control Hypertonic 57.4 mm (6.5) 180 ' 1.82 18 16 1.96 %o 21.83 %o - 62 -B. Control Experiments The f r y moved r a p i d l y from t h e i r o r i g i n a l compartments and the f i r s t non-significant chi-square value was recorded at 30 minutes (Fig. 17). Thereafter, the d i s t r i b u t i o n was uniform (at the 95$ l e v e l of significance) except at 170 minutes. In view of the general constancy of the chi-square values, t h e i r low summation value, and the low value of the s t a t i s t i c s at t h i s period of observation i t i s u n l i k e l y that the d i s t r i b u t i o n occurred by other than chance. Therefore i t i s u n l i k e l y that any factor such as was noted i n the chum and pink experiments operated on these f r y . C. . Reactions of Fry to Seawater (1) Response to Isotonic Seawater The f r y responded r a p i d l y and p o s i t i v e l y to i s o t o n i c seawater (Fig.17) . The f i r s t s i g n i f i c a n t chi-square value was recorded at 50 minutes when 76.9$ of the f r y were noted i n the experimental solutions. The number of f r y i n seawater increased slowly from t h i s point reaching a peak of 84.4$ at the l a s t period of observation. Comparison of thi s data with that on the control f r y sho\\«red a s i g n i f i c a n t difference i n d i s t r i b u t i o n at a l l times a f t e r 30 minutes (Table X I I ) . The response of the f r y to isotoni c seawater was c l e a r l y p o s i t i v e . (2) Response to Hypertonic Seawater The data on the response of coho f r y to hypertonic seawater are summarized i n F i g . 17. The curve would appear -63-Pig.17. Response of coho salmon f r y to sea water. to indicate that the fry showed no preference for either freshwater or hypertonic seawater. There was, however, a complicating factor. Fry in the seawater compartments were observed to be concentrated in the upper few centimetres of water, a region known to be more or less isotonic in -concentration (Fig. 6). A rough determination of the ver t i ca l distribution of the fry was made by estimating the number of fry in this upper region as compared to that i n the main body of the seawater compartments. On the average 50$ - 60$ were found in the \"isotonic layer\" which constituted about one third of the tota l volume of each compartment. The ver t i ca l distribution of fry in the freshwater compartments appeared to be uniform. It would seem that the fry preferred isotonic seawater to hypertonic seawater. At any rate, their response to hypertonic seawater was not posit ive. D. Act iv i ty The ac t iv i ty of fry in freshwater (control experiments) and seawater is summarized i n F i g . 18. Fry in seawater were less active than those in freshwater. In general fry in isotonic seawater showed a decrease in act iv i ty , while those in hypertonic seawater exhibited an increase in act iv i ty with time following a low i n i t i a l l eve l . Some indication of an inverse relationship between act iv i ty and response (decreased act iv i ty with increased response) could be seen in fry responding to isotonic seawater. (Fig.19). No such relationship was apparent in either the -65-O CONTROL O ISOTONIC O HYPERTONIC 15 30 90 BO TIME 110 140 170 Pig.18. A c t i v i t y of coho salmon f r y 1 -66-Pig.19. Activity-response relationship i n coho salmon f r y . - 67 -control or hypertonic s e r i e s . SMOLTS A. Observations on Behaviour During the period of acclimation the smolts swam slowly throughout the whole water mass of t h e i r compartments. There was l i t t l e evidence of orientation to the currents produced by the aerators. Nipping was prevalent i n most cases, although e n t i r e l y absent i n several groups. H i e r a r c h i a l systems were observed i n a few tanks but not i n most. Following the establishment of the \"freshwater bridge\", the smolts began to move slowly over the p a r t i t i o n s i n losse aggregations or as indiv i d u a l s rather than i n schools such as were observed i n the experiments on-pink and chum f r y . In a few cases the smolts began \"nosing\" over the p a r t i t i o n s before the bridges were completely formed. L i t t l e nipping was observed- among f i s h which had entered seawater. B. Control Experiments The movement of the smolts into the alternate freshwater compartments took place slowly (Fig. 20). The f i r s t non-s i g n i f i c a n t chi-square value was not recorded u n t i l 50 minutes a f t e r flooding (Table X I I I ) . After t h i s time the d i s t r i b u t i o n , while nearly uniform, showed a bias i n favour of the tanks i n which the f i s h had o r i g i n a l l y been placed. Summation of the chi-square values from 50 to 200 minutes gave a value exceeding the c r i t i c a l l e v e l f o r 99$ s i g n i f i c a n c e . The d i s t r i b u t i o n - 68 -therefore, probably did not occur by chance, and may have been the result of factors s imilar to those which appeared to be operating on 'chum and pink fry under the same conditions. C. Response to Hypertonic Seawater Since a positive response to isotonic seawater had already been demonstrated in coho fry the smolts were tested only against hypertonic seawater. Their response was positive but took place slowly (Fig.20). However, a l l chi-square values after the f i r s t hour of observation were a l l well above the c r i t i c a l level for 99.5$ significance (Table XIII) . An intermediate peak response was recorded at 110 minutes when 77.8$ of the smolts were observed in the test solution. Following this the number of f i sh in the test solution decreased slowly to 72.2$ at the f ina l observation. Comparison of this distr ibution with that of the control f ish showed that there was a significant difference in response at a l l times after 30. minutes (Table XIV). The response of the smolts to hypertonic seawater was clearly posit ive. Comparison of the responses of coho fry and smolts to hypertonic seawater gave values exceeding the c r i t i c a l l eve l for 95$ significance after 50 minutes (Table XIV). The behaviour of smolts was therefore s ignif icant ly different than that of f r y . D. Act iv i ty The act iv i ty of smolts in both freshwater and seawater -69-60 50 50 60 Pig.20. Response of coho salmon smolts to hypertonic sea water. - 70 -was lower than t h a t o f any other group t e s t e d ( F i g . 21). The changes i n a c t i v i t y with time were s i m i l a r t o those observed i n unacclimated chum f r y (Fig-.IO). The c o n t r o l smolts had an i n i t i a l l y h i g h a c t i v i t y (0 t o &0 minutes) f o l l o w e d by a d e c r e a s i n g l e v e l u n t i l the end of o b s e r v a t i o n . The smolts i n seawater, on the ot h e r hand, were i n i t i a l l y i n a c t i v e , but g r a d u a l l y became more a c t i v e as the experiment p r o g r e s s e d . An i n v e r s e r e l a t i o n s h i p between a c t i v i t y and response o f the smolts t o seawater i s i n d i c a t e d by F i g . 22. -71-60 0 I 0 5 15 30 SO 80 110 140 170 TIME Fig.21. A c t i v i t y of coho salmon smolts. 6.0 X 80 7 0 60 9 0 4 0 90 1 0 10 0 10 2 0 SO 4 0 (-) CHI SQUARE VALUES (+) Fig.22. Activity-response relationship in coho salmon smolts. - 73 -DISCUSSION Behaviour During Control Experiments A tendency to remain i n the o r i g i n a l compartments was manifested by chum and pink f r y and by coho smolts. This pattern of behaviour, most apparent i n chum f r y , was less marked i n coho smolts, and l e a s t noticeable i n pink f r y . Two possible hypotheses can be suggested to account f o r t h i s behaviour. The f i r s t i s based on response to v i s u a l s t i m u l i , the second on response to olfactory s t i m u l i . The f i s h may have the a b i l i t y to apprehend and remember s p a t i a l r e l a t i o n s h i p s . Maintainance i n t h e i r o r i g i n a l compartments would then be the r e s u l t of a preference f o r \"recognized\" areas. A l l compartments had a uniform colour background, but v i s u a l cues may have been present i n the po s i t i o n and form of sampling siphons, and the p o s i t i o n and angle of the aerators and t h e i r supply l i n e s . Recognition of area must be an important f a c t o r i n species which occupy and defend t e r r i t o r i e s , i e . coho f r y . However, coho f r y did not display t h i s preference reaction. It i s therefore u n l i k e l y that the hypothesis can account f o r t h i s pattern of behaviour unless the uniform d i s t r i b u t i o n apparent i n control experiments on coho arose as a r e s u l t of very strongly t e r r i t o r i a l i n d i v i d u a l s d r i v i n g most of other fi s h e s i n t h e i r groups into the alternate compartments. Several investigations point to the p r o b a b i l i t y that o l f a c t o r y cues were more important than v i s u a l cues i n t h i s 1 - 74 -response. Wrede (1932) noted that the olfactory sense played a part i n the aggregation of certa i n species into schools. In t h i s investigations he found that European minnows (Phoxinus) responded p o s i t i v e l y to a substance present i n the mucus from t h e i r skins. He also noted that once assembled into schools, the f i s h appeared to be les s active than when dispersed. Wrede came to the conclusion that species odours play an important part i n the formation and maintainence of f i s h schools. G8z (1941, c i t e d by Hasler, 1954), using the technique of conditioned response on f i f t e e n species of fish, claimed to have demonstrated the presence of c h a r a c t e r i s t i c schooling odours recognizable by the members of a school and important to t h e i r behaviour. More recently, Keenleyside (1955) found that rudd (Scardinius erythrophthalmus Linnaeus), a schooling species, a f t e r being blinded, swam more slowly on entering an area i n which they could detect the odour of t h e i r species. Chum and pink f r y , and to a l e s s e r extent, coho smolts are known to school (Hoar 1951 a) and i t i s possible that they have a- c h a r a c t e r i s t i c odour important i n the i n i t i a t i o n and maintainance of t h i s a c t i v i t y . The concentration of such a material might be b u i l t up during the acclimatory phase of the experiments and might then exercise an a t t r a c t i o n f o r the f i s h during the period of observation. I f such a f a c t o r were responsible f o r the behaviour observed, the decrease i n preference indicated by the - 75 -d i s t r i b u t i o n curve of the chum f r y may be a t t r i b u t e d to two f a c t o r s : exchange of water between compartments, and deposition of increasing amounts of the a t t r a c t i v e material i n the alternate compartments with time. Pink f r y did not display t h i s preference to the same degree as chum f r y or coho smolts. This difference i n behaviour may be related to the continued high l e v e l of a c t i v i t y exhibited by pink f r y . In these experiments a marked a c t i v i t y would tend to reduce the e f f e c t of both o l f a c t o r y and v i s u a l s t i m u l i on any pattern of behaviour requiring concentration i n r e l a t i v e l y small areas f o r i t s expression. The concentration at which these substances ( i f they exist) produce a response must be quite low. Measurements of the t o t a l concentration of dissolved material made i n several of the experiments by means of a dipping refractometer f a i l e d to show any s i g n i f i c a n t differences i n concentration. However, Hasler (1954) has demonstrated the extremely high s e n s i t i v i t y of many species of f i s h to dissolved organic material i n t h e i r surroundings. Further investigation of the nature of t h i s \"preference reaction\" might be p r o f i t a b l e . It was apparent, nevertheless, that responses to s a l i n i t y gradients are not greatly hindered by i t s opertation. S e n s i t i v i t y to Seawater The demonstration of p o s i t i v e responses to seawater i n the three species indicates the presence of s a l i n i t y receptors i n - 76 -t h e i r sensory equipment. Few data are av a i l a b l e on e i t h e r the nature or capacity of such receptors i n P a c i f i c salmon. These experiments show that chum f r y can distihguishlibetween o, solutions of r e l a t i v e l y low concentrations, i e . 2 - 5 /oo. They may not, however, be able to detect the lower concentration. Shepard (1948) estimated that the threshold o o discrimination of chum f r y l a y at between 1.97 /oo and 3.26 /oo, while the work of B u l l (1938) and Krinner (1934) suggests that even lower thresholds.may e x i s t . E f f e c t of Seawater on A c t i v i t y Measurement of the a c t i v i t y of the f r y and smolts during the course of t h i s study showed that i n the majority of cases f i s h entering seawater f o r the f i r s t time became r e l a t i v e l y i n a c t i v e . Several authors have noted that the a c t i v i t y of f i s h was related i n some way to the s a l t concentration of t h e i r environment. Loevy (1938., c i t e d by Black 1951a) found that several species of marine fishes became extremely i n a c t i v e when transferred to seawater at greater than normal s a l i n i t y (approximately 5 0 ^ 0 0 ) . Huntsman and Hoar (1939) made the following comment on the behaviour of migrating A t l a n t i c salmon smolts \"... they are quite i n a c t i v e f o r a time when entering seawater abruptly and may be seen near the bottom ...\". Smith (1955, personal communication) observed that sockeye salmon smolts became quiescent f o r several hours on passing r a p i d l y into regions of f a i r l y high s a l i n i t y . - 77 -Fontaine, Callamand and Vibert (1950) mentioned a condition of d e b i l i t y as being c h a r a c t e r i s t i c of A t l a n t i c salmon during t h e i r seaward migration following spawning. They suggested that t h i s might be attributable to the demineralization of these f i s h while i n freshwater. Eels are also known to be profoundly influenced by the s a l i n i t y of t h e i r medium. Van Heusdan (1943, cited by Fontaine and Koch 1950) demonstrated a r e l a t i o n s h i p between the a c t i v i t y of these f i s h under experimental conditions and the s a l i n i t y of the water i n which they had been held p r i o r to observation. The e f f e c t of s a l i n i t y on a c t i v i t y must be related i n some way to changes which t h i s factor produces i n the metabolism of the f i s h . Such changes would, i n turn, be l a r g e l y conditioned by the state of the f i s h at the time of migration. Black (1951b) has shown that a s i g n i f i c a n t increase i n the water content of chum salmon f r y occurred i f these f i s h were held i n freshwater u n t i l September, a time well past t h e i r normal period of migration. During the same period t h e i r density decreased from 1.007 to 1.001. Both observations indicated an increase i n the absorption of water, and hence a break-down i n the effeciency of t h e i r osmotic control. Black thought t h i s might be due to an increase i n the r a t i o of cholesterol to f a t t y acids i n the tissues, a fac t o r important i n control of the imbibition of water. Fontaine (1951) found a difference i n the concentration of body chlorides i n the parr and smolt stages of the A t l a n t i c - 78 -salmon. The average concentration of chloride i n the muscles of the former stage was 0.318 gm chloride per kgm fresh ti s s u e , and only 0.26 gm chloride per kgm fresh t i s s u e i n the muscles of smolts trapped en route to the sea. A loss of body s a l t s was indicated by these r e s u l t s , and hence reduction of osmotic e f f i c i e n c y . Black (1951 b), on the other hand, did not f i n d a s i g n i f i c a n t change i n the concentration of body chlorides i n chum salmon held i n freshwater past the middle of the summer. Both authors, however, described a loss i n osmotic control, and t h i s might be expected to r e s u l t i n increased water absorption and decreased s a l t content i n the f i s h as long as they remained i n freshwater. Hoar and B e l l (1950) noted a high mortality i n chum and pink salmon held i n freshwater. They were also of the opinion that t h i s might be due to the poor osmotic adjustment of the f i s h to freshwater a f t e r t h e i r normal time of migration. Black's:research (1951 b) also dealt with the absorption of chlorides by chum salmon f r y transferred from freshwater to seawater. Chloride content was determined f o r the whole, f i s h following drying. A marked r i s e i n the body chloride l e v e l occurred within two to three hours a f t e r t ransfer to hypertonic seawater. The rate of absorption varied as the s a l i n i t y of 0/ the water used. In seawater with a s a l i n i t y of 31 /oo the l e v e l increased from 50 to 78 m.eq. chloride per kgm. dry weight i n s i x hours, while i n water at a concentration of 7.1°/00 the increase was from 50 to 64 m.eq. chloride per kgm. - 79 -i n the same length of time. In more d i l u t e seawater (15 °/oo), the increase i n s i x hours was from 50 to about :58 or 60 m.eq. chloride per kgm. Fontaine (195D pointed out that differences i n the ion concentrations of the parr and smolt of the A t l a n t i c salmon were to be found i n the muscles rather than i n the serum or whole blood. Determinations of the ions present i n the muscles of carp placed i n water of varying s a l i n i t y have been reported by several authors. Drilhon and Pora (1936) and Drilhon (1937) found that i n s a l t concentrations somewhat greater than isotonic, carp muscles took up calcium, magnesium, and sodium, but l o s t potassium. They postulated that the muscle tissues acted as a reservoir f o r the excess absorbed ions u n t i l active osmoregulatory processes could remove them. It i s i n t e r e s t i n g to note i n t h i s regard that there was l i t t l e compensation i n the carp a f t e r twenty-four hours, but that a return t o normal l e v e l was found i n chum salmon f r y a f t e r twelve hours, (Black 1951 b), and a f t e r only three hours i n the eel (Pora 1937). The conclusion that muscle tissue acted as an \"ion reservoir\" was reached e a r l i e r by Kaplansky and Boldyrewa (1933, c i t e d by Drilhon, 1937, and Black 1951 a). These authors concluded that only cations entered the tissues, where they were held i n undissociated form. The same hypothesis was also advanced by Black (1951 b) who stated \" I t seems apparent that i n the salmon and eel the tissues supply a temporary storage place f o r s a l t s u n t i l regulation by the g i l l s and kidneys i s accomplished.\" - 80 -The e f f e c t of i n d i v i d u a l ions on muscle tissue has been ably reviewed by Heilbrunn (1952) and Scheer (1953). The former author noted that sodium ions caused i n d i v i d u a l f i b r e s and groups of f i b r e s to contract independently, so that the muscle as a whole appeared to quiver. Scheer believed that an excess of sodium ions caused a polymerization of the muscle proteins r e s u l t i n g i n the formation of gels. Calcium was thought to exert an e f f e c t by inducing a general surface p e r c i p i t a t i o n reaction i n the protoplasm of the f i b r e s . Magnesium i s well known f o r i t s general depressing influence on protoplasmic processes. In the publications of Szent-Gyorgyi (1948) and Mommaertes (1950) there i s a more detailed account of the actual biochemistry of muscle, and the effects of various factors including ions on the mechanism of muscle action. The functional proteins involved i n muscular contraction and relaxation are myosin and a c t i n . Both authors were careful to point out that these terms r e f e r to states of organization rather than to discrete molecular e n t i t i e s . Muscular tension i s exerted when actin, i n the fibrous' state, combines with myosin to form the complex actomyosin. The formation of t h i s complex appears to be s i m i l a r i n some ways to a p r e c i p i t a t i o n reaction. The two components, which normally e x i s t i n the disassociated, mutually repulsive state, are neutralized and form polymers. This polymerization i s accompanied by a shrinkage, and hence the muscle as a whole contracts. Adenosinetriphosphate and several ions play important - 81 -roles i n the n e u t r a l i z a t i o n reaction of a c t i n and myosin. Actomyosin i n the presence of adenosinetriphosphate i s a stable complex only within a very narrow range of ion concentrations. Because of th i s i t exists either i n the form of i t s charged components or i n the t o t a l l y contracted actomyosin state. Szent-Gyorgyi presented data on the behaviour of actonryosin threads i n various cone ent rat ions of potassium chloride. Maximum contractions were seen to occur at s l i g h t l y l e s s than isotonic concentrations (about 0.-16 M) and decreased on either side of t h i s point, abruptly at higher concentrations and more slowly at lower concentrations. Szent-Gyorgyi found, moreover, that the action of potassium while e s s e n t i a l was not s p e c i f i c . Potassium could be replaced by sodium, and nother monovalent ions. An increase i n the sodium concentration of the muscles as noted by Drilhon (1937) could therefore produce a marked e f f e c t on muscle e f f i c i e n c y . The e f f e c t of potassium concentration on the absorption of adenosinetriphosphate, which i s essential i n the c o n t r a c t i l e process, was also considered by Szent-Gyorgyi. At values below 0.1 M adenosinetriphosphate absorption was sharply decreased. Therefore the release of potassium by muscle which occurs i n hypertonic solutions must cause a concommitant ••release of absorbed adenosinetriphosphate, and thus disturbs the normal course of events i n muscle contraction. Mommaertes (1950) reported that calcium ions had no act i v a t i n g e f f e c t on contraction, and a c t u a l l y i n h i b i t e d i t . - 82 -He also pointed out that as the l e v e l of potassium was increased the range of potassium concentrations within which contraction would occur was decreased. Hence with increase i n both sodium and magnesium occurring i n the muscles of f i s h entering seawater the contraction of the f i b r e s would be hindered. Thus i t can be seen hovx the i n t e r a c t i o n of absorbed ions with the muscle proteins of f i s h entering seawater could t h e o r e t i c a l l y r e s u l t i n decreased a c t i v i t y through .a lowering of the e f f i c i e n c y of c o n t r a c t i l e processes. I f the foregoing hypothesis i s admitted the behaviour observed i n t h i s i n v e s t i g a t i o n can be p a r t i a l l y accounted f o r . Fish entering seawater f o r the f i r s t time would absorb ions which would be deposited on the body muscles u n t i l such time as the osmoregulatory mechanism began to function. U n t i l t h i s time the presence of these ions would i n t e r f e r e with the normal metabolism of the muscle, decreasing i t s e f f i c i e n c y and hence the a c t i v i t y of the f i s h . This would account f o r the negative slope of the activity-response curve seen i n the chum f r y and coho smolts. The f i s h responded p o s i t i v e l y to the seawater solution, and were gradually affected by i t i n such a way as to decrease t h e i r a c t i v i t y . The combination of the o r i g i n a l p o s i t i v e response and the l a t e r reduced mobility i n seawater accounts f o r the very strong intermediate response noted i n these species. The gradual increase i n a c t i v i t y observed i n chum f r y and coho smolts reacting to hypertonic seawater may be ascribed to two f a c t o r s : acclimation of the muscles to the presence of excess ions, and/or the gradual removal of ions by the process of osmoregulation. Hoar (194-8) has observed c y t o l o g i c a l indications of the presence of \"chloride secreting c e l l s \" i n the g i l l s of pink and chum salmon f r y , but not i n those of the coho f r y . However, Black's work (1951 b) indicated that osmoregulation did not occur u n t i l chum f r y had been i n seawater . f o r at l e a s t twelve hours. These data would seem to discount the second of the two possible explanations, but as yet no explanation can be advanced f o r t h i s behaviour. Much the same process must have occurred i n the f r y entering isotonic seawater. The uptake of ions would be slower than that found i n . f r y entering hypertonic seawater, and the f i n a l concentration of ions i n the body l e s s . However, Szent-Gyorgyi indicated that a change i n the potassium l e v e l of only a few percent of the i n i t i a l value was s u f f i c i e n t to produce a r e l a t i v e l y large e f f e c t on muscle action. The f a c t that a c t i v i t y f e l l o f f more slowly i n chum f r y entering isotonic seawater but eventually reached the same l e v e l as that of the f r y entering hypertonic seawater, tends to bear out t h i s theory. Reactions of Pink Salmon Fry Compared With Other Species In several instances the behaviour of pink f r y d i f f e r e d from that of e i t h e r chum f r y or coho f r y and smolts under s i m i l a r conditions. The a c t i v i t y of pink f r y , i n contrast to that of the other two. species, remained uniformly high - 84 -throughout the whole period of observation. In addition, they exhibited a d i r e c t r e l a t i o n s h i p between a c t i v i t y and response (as opposed to the inverse r e l a t i o n s h i p usually'seen i n chums and coho), and t h e i r responses to seawater are les s marked than those of chum f r y or coho smolts. This may not hold true under natural conditions. Q u a l i t a t i v e observations on pink f r y i n a r t i f i c a l surroundings indicate a consistently lower stimulation threshold f o r a c t i v i t y than i s seen i n the other two species. The high l e v e l of a c t i v i t y which was observed may have been the r e s u l t of successive physical s t i m u l i such as the operation of the sampling siphons, of vibrations i n the building i n which the apparatus was housed, and of s i m i l a r agencies. Under natural conditions such s t i m u l i are probably not present, and the behaviour of pink f r y might then be comparable to that of chums and coho. The hypothesis that pink f r y have a lower threshold of stimulation was i n d i r e c t l y strengthened by the observation that pink f r y held under the same conditions as chum and coho 1 i had a much higher mortality rate than did the other two species. Few pink f r y survived past the end of June, whereas chum f r y were available u n t i l l a t e November, and coho throughout the winter. This indicated, among other things, that the pink f r y were l e s s well adjusted osmotically than chums or coho. Hoar and B e l l (1950) found that h y p e r p l a s t i c i t y of the thyroid, was associated with the retention of pinks and chums in freshwater past t h e i r normal time of migration. They believed that t h i s extreme a c t i v i t y was the r e s u l t of osmotic - 85 -st r e s s . However, thyroid derivatives possess an influence on body processes other than osmoregulation. Hoar, MacKinnon and Redlich (1952), and Hoar Keenleyside and Goodall (1955), found that chum salmon f r y , and yearling coho and sockeye exhibited increased a c t i v i t y following treatment by thyroxine. Hoar i n an e a r l i e r paper (1953) and Hoar, Keenleyside and Goodall ( l o c . c i t ) postulated that the source of t h i s a c t i v i t y lay i n the s e n s i t i z a t i o n of the central nervous mechanisms to external s t i m u l i . Presumably natural hyperthyroidism could produce this r e s u l t also, and would account f o r the high l e v e l o f , a c t i v i t y observed i n the experimental f i s h . The difference i n the a c t i v i t y and mortality of chum and pink f r y of about the same size may have been a r e s u l t of the general hardiness of the former species. An al t e r n a t i v e explanation might be that the thyroid a c t i v i t y of the chum f r y was not as great as that of the pink f r y . Pink f r y from the Oyster River, Vancouver Island, migrate seaward somewhat e a r l i e r than do' chum f r y from Cultus Lake. Moreover, the chum f r y used i n these experiments were f i s h which had been hatched and reared i n a hatchery, and i t i s probable that t h e i r development was behind that which might be expected of f i s h under natural conditions. Response of Coho Salmon Fry and Smolts to Seawater. The response of coho f r y to hypertonic seawater was not positive, i n contrast to that of pink and chum f r y , although - 86 -a p o s i t i v e reaction to isotonic seawater was demonstrated. Shepard (1948) reported that coho f r y avoided seawater at a l l concentrations. The difference i n the sign of the response to d i f f e r e n t concentrations may be related to the fac t that l e s s metabolic work i s required of animals i n media isotonic to t h e i r own body concentrations. It i s d i f f i c u l t to v i s u a l i z e a mechanixm to account f o r t h i s variable response. Possibly the threshold l e v e l s of neuromotor reflexes r e s u l t i n g in;,avoidance reactions are higher than those related to preference reactions. The change i n response of coho to hypertonic seawater which occured with age provides another example of developmental convergence i n the behaviour pattern of juvenile P a c i f i c salmon. Hoar (1953, 1954) has-.already pointed out that the cover reactions, t e r r i t o r i a l behaviour, depth preference, phototactic response, and rheotrophic reactions of coho change with age f o r a form approximating those seen i n chum and pink f r y . These reactions are responsible f o r t h e i r downstream movement. To t h i s l i s t may now be added responses to seawater. \"Exploratory\" and \"Preference\" A c t i v i t y D i v i s i o n of the a c t i v i t y of chum f r y and coho smolts into two phases, \"exploratory\" and \"preference\" has already been noted. The f i r s t of these phases must be considered to ar i s e from the experimental conditions, under which the study ' was carried out. Newman (1955, personal communication), i n - 87 -i n v e s t i g a t i o n of the ethology of salmonoid fis h e s , found that f i s h placed i n new surroundings exhibit \"escape behaviour\" characterized by r e s t l e s s swimming back and forth, up and down, along the walls of the new aquaria. The ^exploratory phase\" of behaviour described i n the present experiments was probably an expression of t h i s \"escape behaviour\". Preference reactions occurred with a lessening of i t s i n t e n s i t y . i Decrease i n Response With Time Unacclimated chum f r y , pink f r y , and coho smolts exhibited a decreased response to seawater with time, which was usually coupled with an increase i n a c t i v i t y . Two hypotheses to account f o r t h i s may be suggested: accomodation of sensory receptors, and lessened e f f e c t of absorbed seawater ions on motor a c t i v i t y . Since the response of osmotically adjusted chum f r y continued to increase with time, i t i s un l i k e l y that the source of the decreased response i s to be found i n decreased o l f a c t o r y capacity. On the other hand, the work of Black (1951 b) suggests that osmotic regulation i n chum salmon f r y does not have an e f f e c t on the concentration of absorbed ions u n t i l about twelve hours a f t e r the f i s h had entered seawater. Possibly, the body muscles accomodate i n some way to high concentration of e l e c t r o l y t e s which allows an increase i n t h e i r e f f i c i e n c y . I - 88 -Relationship of Seawater to Seaward Migration : Emphasis has already been l a i d on the f a c t that s a l i n i t y gradients can have l i t t l e influence on the movements of young P a c i f i c salmon during the freshwater., portion of t h e i r seaward migration. This may be ascribed to fluctuations i n the d i r e c t i o n of such gradients under the influence of t r i b u t a r i e s , and to the low rates of change of concentration with distance. Rheotropic responses appear to be the major f a c t o r i n the orientation of these f i s h i n streams and r i v e r s (Hoar 1951 b, 1953, 1954), MacKinnon and Hoar 1953), but t h i s type of behaviour would tend to maintain the migrants i n r i v e r outflows i n d e f i n i t e l y unless counteracted by other e f f e c t s . Two factors contribute to reduce the importance of rheotropisras. F i r s t , the strength and pattern of currents i s less marked i n r i v e r mouths and estuaries than i n r i v e r s themselves. Secondly, i t appears that seawater, through i t s influence on motor a c t i v i t y , may have the p o t e n t i a l i t y of reducing the degree to which f i s h can display rheotropic reactions. Reduction i n motor a c t i v i t y would also increase the p r o b a b i l i t y of passive displacement seaward by current - ac t i o n . F i n a l l y , any remaining a b i l i t y to react against currents would increase movement out to sea during periods of t i d a l inflow. The positive responses of migrants entering seawater, which have been demonstrated in.both osmotically adjusted and unadjusted f i s h , would also tend to cause an active movement of f r y and smolts from r i v e r mouths and estuaries out to sea. - 89 -In summary i t may be said that seawater probably influences migration through r i v e r mouths and estuaries by counteracting rheotropic responses and by acting as a d i r e c t i v e influence i n the movements of these f i s h . - 90 -SUMMARY (1) Chum and pink salmon f r y respond p o s i t i v e l y to both is o t o n i c and hypertonic seawater, whereas coho f r y show a preference f o r isotonic seawater, and do not respond p o s i t i v e l y to hypertonic seawater. (2) Coho smolts, i n contrast to coho f r y , show a preference for hypertonic seawater. (3) The a c t i v i t y of f r y and smolts not previously acclimated to seawater decreases following entry into seawater. Experiments on chum f r y acclimated to seawater before observation of t h e i r responses to seawater suggest that reduction i n a c t i v i t y may be associated with osmotic regulation. It i s postulated that reduction i n a c t i v i t y results from interaction.of absorbed e l e c t r o l y t e s with muscle protein. (4) Two possible effects of B-eawater on seaward migration are discussed: (a) the e f f e c t of absorbed ions on the reduction of rheotropic responses through r e s t r i c t i o n of general motor a c t i v i t y , (b) the importance of po s i t i v e responses to s a l i n i t y gradients which may lead juvenile P a c i f i c salmon towards the open ocean. (5) The presence of preference reaction f o r the compartments i n which they were o r i g i n a l l y placed has been demonstrated i n control experiments on pink and chum f r y , and coho smolts. The possible influence of v i s u a l and o l f a c t o r y s t i m u l i i n t h i s preference reaction has been discussed. LITERATURE CITED (1) Alderdice, D.F., Brett, J.R., Idler, D.R., and Fagerlund, U. 1954. Further observations on olfac t o r y perception i n migrating adult coho and spring salmon - Properties of the repellent i n mammalian skin. F i s h . Res. Bd. Canada., Pac. Prog. Rept. No. 98: 10-12. (2) Black, E.C. 1954. Blood l e v e l s of hemoglobin, glucose, and l a c t i c acid following a c t i v i t y i n some freshwater f i s h e s . Prog. Rept. Assoc. Comm. Res. Aquatic. B i o l . , Nat. Res. Council., Canada. (3) 1955* Blood l e v e l s of hemoglobin and l a c t i c acid i n some freshwater fishes following exercise. J. F i s h . Res. Bd. Canada. 12: 917-929. (4) Black, V.S. 1951a. Osmotic regulations i n tele o s t f i s h e s . Univ. Tor. B i o l . Ser. No. 59. Pub. Ont. Fi s h . Res. Lab. No. 71: 53-89. (5) 1951b. Changes i n body chloride, density, and water content of chum (Oncorhyncus keta) and coho (Ch kisutch) salmon f r y when transferred from freshwater to seawater. J . F i s h . Res. Bd. Canada. 8: 164-177. (6) Brett, J.R., and MacKinnon, D. 1952. Some observations on o l f a c t o r y perception i n migrating adult spring and coho salmon. F i s h . Res. Bd. Canada., Pac. Prog. Rept. No. 90: 21-23. (7) B u l l , H.O. 1938. Studies on conditioned responses i n f i s h . Part 8. Discrimination of s a l i n i t y changes i n marine t e l e o s t s . Rept. Dove Mar. Lab. 3rd Ser. 5' 19-35. (8) Callamand, 0., and Fontaine, M. 1940. Sur l e determinisme biochimique du retour a l a mer de l ' a n g u i l l e femelle d'avalaison. C.R. Acad. S c i . Pa r i s . 211: 357-359. (9) Can. Joint Comm. Oceanog. 1950. Manual of Oceanographic Methods. (10) Chidester, F.E. 1922. Studies on f i s h migration. 2. The influence of s a l i n i t y on the d i s p e r s a l of f i s h e s . Amer. Nat. 56: 373-380. (11) Clemens, W.A. 1951. On the migration of the P a c i f i c salmon (Oncorhynchus). Proc. Roy. Soc. Canada. 45., Ser. I I I . , Sec. 5: 9-17. - 92 -(12) Col l ins , G.B. 1952. Factors influencing the orientation of migrating anadromous fishes. U.S. Dept. Inter. , Fish and Wildl i fe Ser. , F ish . B u l l . No. 585., Woods Hole Oceanog.-\"Inst. (13) Craigie, E . H . 1926. A preliminary experiment on the relation of the olfactory sense to the migration of the sockeye salmon [0^ nerka Wal.) . Trans. Roy. Soc. Canada. 20: 215-224. (14) Doudoroff, P. 1938. Reactions of marine fishes to temperature gradients. B i o l . B u l l . 75J 494-509. (15) Drilhon, A. 1937. Etude des eschanges mineraux chez les poissons homeiosmotique. C R . Acad. S c i . Paris . 204: 1502-1503. (16) Drilhon, A . , and Pora, E . A . 1936. Regulation mineral du milieu interieur chez les poissons stenohalines, Ann. Physiol. Physicochim. B i o l . 12: 139-168. (17) F i sh . Res. Bd. Canada. 1953. Observation of seawater temperature and sa l in i ty on the Pacific coast of Canada. Data Rept. Pac. B i o l . Stn. and Pac. Oceanog. Grp. F i sh . Res. Bd. Canada. Pub., V o l . 8. (18) F j a r l i e , R . L . I . 1950. The oceanographic phase of the Vancouver sewage problem. Pub. Can. Joint . Cornm* Oceanog. (19) Fontaine, M. 1943. Des facteurs physiologique determinant les migrations des cyclostomes et poissons'potamotoques. B u l l . Inst. Oceanog., Monaco. 40: 1-8. (20) : : 1948. Du role joue par les facteurs internes dans certain migrations des poissons: Etude critique des diverses methodes d'investigation. J . du Conseil Internat. pour l 'Exp lor . de l a Mer. 15: 284-294. (21) 1951a. Facteurs externes et internes regissant les migrations des poissons. Colloque Internat. E c o l . , Ann. B i o l . 27. Fasc. 7: 337-348. (22) 1951b. Sur diminuition de l a tenure en chlore du muscle des jeunes saumons (smolts) lors de l a migration d'avalaison. C R . Acad. S c i . 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(28) Fontaine, M. , and Vibert, R. 1952 Migration f luviale anad.fome du saumon (Salmo salar L .T et gradient de sa l ln i t e . Ann. Stn. Cent. d'Hydrobiol. App. 4: 339-345. (29) Fry, E . E . ' J . 1947. Effects of the environment on animal ac t iv i ty . Univ. Tor. B i o l . Ser. No. 55., Pub. Ont. F i sh . Res. Lab. No. 68: 5-62. (30) Foerester, R . E . 1937. The relation of temperature to the seaward migration of young sockeye salmon (0^ nerka). J . B i o l . Bd. Canada. 3: 421-438. (31) Hasler, A.D. ' 1954* Odour perception and orientation in fishes. J . Fish Res. Bd. Canada. 11: 107-129. (32) Hasler, A .D. , and Wisby, W.J. 1951. Discrimination of stream odors by fishes and i t s relation to parent stream behaviour. Amer. Nat. 85J 223-238. (33) Heilbrunn, L . V . 1952. An Outline of General Physiology. 3rd Ed. W.B. Saunders Co. New York. (34) Hoar, W.S. 1948. Unpub. data. (35) 1951a. The behaviour of pink, chum and coho salmon in relation to their seaward migration. J . F ish . Res. Bd. Canada. 8: 241-263. (36) 1951b. Hormones in f i s h . Univ. Tor. B i o l . Ser. No. 59. Pub. Ont. F i sh . Res. Lab. No. 71: 1-51. (37) 1953* Control and timing of f i sh migration. Biol . -Rev. 28: 437-452. . (3g) _ 1954. The behaviour of the juvenile Pacific salmon with part icular reference to the sockeye (Oncorhynchus nerka). J . F i s h . Res. Bd. Canada. 11: 69-97. - 94 -1956. The behaviour of migrating pink and chum salmon f r y . J. Fi s h . Res. Bd. Canada, (i n press). Hoar, W.S., and B e l l , G.M. 1950. The thyroid gland i n r e l a t i o n to the seaward migration of P a c i f i c salmon. Can. J . Res. D. 28: 126-138. Hoar, W.S., Keenleyside, M.H.A. and Goodall, R.G. 1955. The effects of thyroxine and gonadal steroids on the a c t i v i t y of salmon and g o l d f i s h . Can. J. Zool. 33: 428-439. Hoar, W.S., MacKinnon, D., and Redlich, A. 1952. E f f e c t s of some hormones on the behaviour of salmon f r y . Can. J. Zool. 30: 273-286. Hora, S.L. 1952. Further evidence from d i s t r i b u t i o n of the r i s e i n s a l i n i t y of the River Hooghly. Curr. S c i . Feb: 49-50. Huntsman, A.G. 1945a. Variable seaward migration of salmon. J. F i s h . Res. Bd. Canada. 6: 311-325. 1945b. Migration of salmon parr. J . F i s h . Res. Bd. Canada.. 6: 399-402. 1948 a. Salmon and animal migration. Nature, 161: 300-302. 1948 b. Method i n ecology - b i a p o c r i s i s . Ecology. 29: 30-42. 1950. Factors which may a f f e c t migration. Salmon and Trout Mag. 227-239. Huntsman, A.G., and Hoar, W.S. 1939. Resistance of At l a n t i c salmon to seawater. J. F i s h . Res. Bd. Canada. 4: 409-411. Keenleyside, M.H.A., 1955. Some aspects of the schooling behaviour of f i s h . Behaviour. 8: I83-248. Keenleyside, M.H.A., and Hoar, W.S. 1954. E f f e c t s of temperature on the response of young salmon to water currents. Behaviour. 7: 77-87. MacKinnon, D., and Brett, R.J. 1955. 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Physiol . , 6: 67-98. . - 97 -APPENDIX TABLE V Control data and response of chum salmon f r y to isotonic sea water Time Control Non-acclimated f r y Acclimated f r y Chi-square * % f r y i n o r i g i n a l compartment Chi-square fo f r y i n sea water Chi-square % f r y i n sea water Raw data fo data Raw data % data Raw data fo data 05 -90.44 - 5 0 . I i 85.04 -125.53 -68.00 8.74 . -47.15 -24.75 20.77 15 -40.82 -22.17 73.54 - 28.26 -15.09 30.56 ^ 7.12 - 3.73 38.64 30 -45/66 -24.80 74.90 ** 3.85 1.95 56.99 - 0.82 - 0.39 46.14 50 -51.14 -27.78 76.35 21.81 12.59 67.02 - 0.26 - 0.14 47.82 80 -31.32 -25.24 75.12 39.50 21/16 73.01 - 0.03 - 0.01 51.08 110 -22.72 -13.33 67.56 46.68 25.00 75.03 0.00 0.00 49.87 140 -29.48 -16.00 70.00 58.05 31/36 78.00 3.00 1.57 57.37 170 -22.03 -11.83 67.20 43.34 23.25 74.11 4.06 2.13 58.57 200 -23.67 -12.86 67.93 76.05 40.96 82.03 6.24 3.28 60.63 * C r i t i c a l l e v e l f o r 95$ s i g n i f i c a n c e - 3.84 n n it 99$ n - 6.63 \" ft tt 99.5$ \" - 7.88 #* Unless otherwise indicated chi-square values i n these tables are p o s i t i v e . TABLE VI Comparison of responses of chum salmon fry to isotonic sea water Time Control and unacclimated fry Control and fry acclimated to hypertonic sea water Unacclimated fry and fry acclimated to hypertonic sea water 05 3.35 1.86 9.44 15 0.76 5.42 2.27 30 38.43 15.55 3.70 50; 69.38 20.55 11.92 80 46.21 18.93 16.26 110 66.63 10.02 20.89 140 84.60 7.50 15.59 170 62.62 21.29 8.62 200 92.91 26.08 31.84 TABLE VII Response of chum salmon f r y to hypertonic sea water T\" K Time Non-acclimated f r y Fry acclimated to isotoni c sea water Fry acclimated to hypertonic sea water Chi-square % f r y i n sea water Chi-square f r y i n sea water Chi-square fo f r y i n sea water Raw data fo data Raw data fo data Raw data fo data 05 -40.63 26.35 -12.08 -7.84 35.92 -76.24 -31.09 22.11 15 4.72 2.56 58.01 1.05 0.68 54.09 16.20 6.60 62.85 30 23.21 12.67 67.80 17.00 11.04 66.61 15.36 6.26 62.51 50 71.41 39.06 81.25 15.48. 9.22 65.19 27.22 11.10 66.66 80 116.58 63.81 89.94 32.02 20.81 72.81 a . 9 2 17.09 70.67 110 95.78 52.39 86.19 21.73. 14.11 68.78 39.47 16.00 70.06 140 79.12 43.82 83.08 27.61 17.94 71.10 75.12 30.63 77.67 170 71.41 39.29 81.34 34.83 22.64 73.79 44* 44 18.11 71.28 ' 200 52.77 28.86 76.86 34.83 22.64 73.79 46.43 18.94 71.76 TABLE VIII A Comparison of responses of chum salmon f r y to hypertonic sea water Time Control and unacclimated f r y Control and f r y acclimated to isotonic sea water Control and f r y acclimated to hypertonic seawater 05 7.30 20.61 3.49 15 37.51 26.92 55.87 30 67.40 58.62 59.19 50 122.02 59.92 77.90 80 135.42 63.19 52.22 110 109.86 44.33 59.90 140 105.19 56.93 96.83 170 88.22 56.40 62.89 200 74.21 58.38 66\". 87 TABLE V I I I E Comparison of responses of chum salmon f r y to hypertonic sea water Time Unacclimated f r y and fry-acclimated to i so ton ic sea water Unacclimated f r y and f r y acclimated to hypertonic sea water Fry acclimated to i so ton ic sea water and f r y acclimated to hypertonic seawater 05 3.58 1.04 9.24 15 0.52 1.01 2.97 30 0.05 1.31 0.70 50 10.55 11.31 0.04 80 16.69 23.47 . 0.22 110 14.85 15.88 0.67 140 6.81 1.95 2.09 170 2.76 5.80 0.31 200 0.42 .i 1 • 44 8.20 TABLE IX Control data and response of pink salmon f r y to seawater Control Isotonic Hypertonic Time Chi-square fo f r y i n o r i g i n a l compartment Chi-square % f r y i n seawater Chi-square % f r y i n seawater 05 - 63.33 88.48 - 98.31 8.10 - 80.04 1.20 15 - 39.07 80.22 - 76.25 13.10 - 59.43 7.94 30 - 2.93 57.48-, - 9.56 36.92 - 35.12 17.66 50 - 0.40 53.12 4.34 . 58.80 - O.58 45.84 SO 0.12 48.28 7.18 61.13 2.01 57.73 110 - 2.10 57.00 8.41 62.26 11.72 68.65 140 - 0.10 52.17 1.92 56.81 22.34 75.80 170 - 2.80 61.26 0.81 54.45 20.66 74.80 200 - 0.05 51.52 3.88 59.72 17.19 72.61 230 - 1.27 57.58 5.S7 61.94 11.93 68.85 TABLE X Comparison of responses of pink salmon f r y to seawater Time Control and Isotonic sea water Control and Hypertonic sea water Isotonic seawater and Hypertonic sea water 05 0.82 15.70 4.81 15 2.02 5.31 1.41 30 0.86 13.46 9.11 50 3.47 0.17 3.56 80 1.97 0.00 0.18 110 9.06 12.48 0.94 140 1.51 13.40 7.79 200 0.12 4.34 3.61 230 7.20 11.40 1.03 TABLE XI Control data and response of coho salmon fry to sea water Time Control • Isotonic Hypertonic Chi-square % fry in original compartment Chi-square % fry in sea water Chi-square fo fry in sea water Raw data . % data Raw data % data Raw data fo data 05 -52.50 -25.36 75.18 -33.37 -19.57 27.83 -57.37 -32.83 32.01 15 -18.66 - 8.99 64.99 - 4.03 - 3.03 41.29 - 7.24 - 3.99 39.34 30 -00.04 - 0.02 50.68 - 1.32 0.78 54.41 - 0.45 - 0.24 47.43 50 2.28 1.09 ' 44.70 50.21 29.14 76.99 0.02 0.01 50.41 80 0.74 - 0.35 52.94 50.21 29.14 76.99 - 1.88 - 1.02 44.82 110 - 2.64 - 1.26 55.61 50.58 29.35 77.09 - 1.61 - 0.88 45.20 140 - 1.75 - 0.83 54.56 56.53 . 32.81 78.64 - 2.62 - 1.49 43.89 170 - 4.97 - 2.38 57.72 58.48 33.94 79.13 - 2.96 - 1.62 43.52 200 - 0.86 - 0.41 53.19 81.43 47.31 84.39 - 1.49 - 0.81 45.38 TABLE XII Comparison of responses of coho salmon to sea water Time Contro l and i so ton ic seawater Control and hypertonic seawater Isotonic seawater and hypertonic seawater 05 0.31 0.00 1.53 15 1.00 0.00 0.11 30 0.98 0..00 1.68 50 19.69 0.00 26.84 80 35.56 0.00 38.15 110 41.91 0.00 37.57 140 43.68 0.00 44*64 170 53.08 0.00 46.90 200 57.86 0.00 58.49 TABLE XIII Control data and response of coho salmon smolts to sea water Control Hypertonic Time Chi-square fo f r y i n o r i g i n a l compartment Chi-square fo f r y i n seawater Raw data % data Raw data % data 05 - 145.19 - 120.17 94.81 - 138,91 - 76.28 6.83 15 - 82.69 - 45.72 83.81 . , 70.61 - 38.54 18.95 30 - 17.42; - 9.60 65.49 - 19.13 - 10.50 33.79 50 - 26.96' - 14.89 69.28' \" -. 1.13 - 0.62 46.06 : SO - 0.67 - 0.36 53.00 13.19 7.25 63.46 | 110 - 1.14 - 0.62 53.93 55.32 30.38 77.56 140 - 8.45 4.64 60.77 47.87 26.30 75.64 1 170 - 4.67' - 2.56 58.00 34.00 18.66 71.60 200 - 1.54 O.84 • 54.57 35.75 19.62 72.15 TABLE XIV Comparison of responses of coho salmon smolts Time Contro l and Hypertonic sea water Smolts and f r y to Hypertonic sea water 05 0.244 24.311 15 0.506 14.246 30 0.124 9.564 50 9.046 3.271 80 9.985 10.583 110 38.266 44.506 140 47.083 36.769 170 32.439 36.753 200 26.873 25.701 TABLE XV A c t i v i t y of unacclimated chum salmon f r y Time Ave. no. cross-over movements per f i s h Control Isotonic Hypertonic 05 0.375 0.215 O.56O 15 0.527 0.564 0.709 30 0.554 1.133 O.648 50 0.408 0.641 O.368 80 0.315 0.348 0.181 110 0.326 0.221 Q'.280 140 0.332 0.204 0.253 170 0.250 0.116 0.352 200 0.234 0.309 0.154 0-50 . 0.466 0.638 0.571 50-200 0.291 0.239 0.244 TABLE XVI A c t i v i t y of acclimated chum salmon f r y Ave. no. cross-over movements per f i s h Time . Hypertonic acclimated to hypertonic Hypertonic acclimated to i s o t o n i c Isotonic acclimated to hypertonic 05 0.584 0.941 0.739 15 0.698 0.608 0.804 30 0.873 0.928 0.826 .50 0.714 0.915 0.623 80 0.576 0.680 0.355 110 0.482 0.320 . 0.442 140 0.335 0.477 0.544 170 0.318 0.379 0.319 200 0.380 0.301 0.268 Average:0-50 Average:50-200 0.717 0.418 0.848 0.431 0.744 0.385 TABLE XVII Activity of pink salmon fry Time Ave. no. cross-over movements per fish Control Isotonic Hypertonic 15 0.486 0.207 0.190 30 0.720 0.536 0.310 50 0.766 0.921 0.357 80 0.589 0.757 0.345 110 0.766 0.736 0.536 140 0.621 0.855 0.571 170 0.529 0.745 0.286 200 0.770 0.809 0.441 0-50 0.657 0.554 0.285 50-200 0.655 0.780 0.435 TABLE XVIII A c t i v i t y of coho salmon f r y Time Ave. no. cross-over movements per f i s h Control Isotonic Hypertonic 15 0.835 0.606 0.544 30 •a. 146 0.523 0.727 50 0.937 0.506 0.638 80 0.976 0.677 0.722 110 0.961 0.700 0.622 140 0.810 0.748 0.516 1170 0.786 0.594 0.433 200 0.835 0.571 0.361 Average:0-50 0.972 0.545 O.636 Average:50-200 0.873 0.658 0.531 TABLE XIX Activity of coho salmon smolts Time Ave. no. cross-over movements per fish Control Hypertonic 05 0.138 0.188 15, 0.394 0.084 30 0.333 0.122 50 0.550 0.033 80 0.294 O.O84 110 0.311 0.235 140 • 0.272 0.141 170 0.261 0.264 200 0.094 0.166 : 0-50 0.353 0.106 : 50-200 O.246 0.178 •'TABLE XX Tests of homogeniety of variance Species Series Time Value* Chum Control 200 7.404 Chum Isotonic n o 4.490 Chum Hypertonic 50 3.489 Chum Hypertonic acclimated to hypertonic 110 7.943 ' Chum Hypertonic acclimated to hypertonic 15 3.837 * C r i t i c a l l e v e l f o r 95$ significance 11.070 "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0106300"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Zoology"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "An experimental study of the response of young Pacific salmon to sharp sea water gradients"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/40484"@en .