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An experimental study of some visually released behaviour patterns in young coho salmon and Kamloops… Stringer, George Everett 1952

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AN EXPERIMENTAL STUDY OF SOME VISUALLY RELEASED BEHAVIOUR PATTERNS IN YOUNG COHO SALMON AND KAMLOOPS TROUT by GEORGE EVERETT STRINGER A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS In the Department of ZOOLOGY We accept t h i s thesis as conforming to the standard required from candidates for the degree of MASTER OF ARTS. Members of the Department of Zoology. THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1 9 5 2 . ABSTRACT Coho underyearlings settle toward the bottom when illumination decreases. The c r i t i c a l Intensity for this response was found to be approximately 1 foot candle. A study of the nipping phenomenon in coho and kamloops trout revealed that coho nip more Intensively than trout in a homotypic group. However; in a heterotypic group of equal numbers, trout nip more readi ly . In a heterotypic group coho nip less frequently and show a preference to nip other coho. By comparison, the nipping Intensity of trout is not reduced and they nip either species equally. Factors affecting nipping are size, color and l ight intensity. In a group of coho or trout, there is a marked tendency for the larger members to nip the smaller. Red and orange colors are least effective in e l i c i t i n g a nipping response. Light intensity changes between H- and 12 foot candles have no significant effect; however, below k foot candles nipping declines rapidly as illumination i s decreased. The social releaser for nipping is movement but size and color are Important components of the releaser. Additional patterns of behavior have been vdescribed for trout, namely, "threatening11 and f ighting. TABLE OF CONTENTS INTRODUCTION 1 MATERIALS AND METHODS Se t t l i n g . 4 Nipping and T e r r i t o r i a l Defense 5 Light Intensity .. • • b Social Releaser 9 RESULTS S e t t l i n g 11 Nipping and T e r r i t o r i a l Defense ............ 12 Light Intensity 13 Social Releaser * 14 DISCUSSION Se t t l i n g 17 Nipping 1 9 Light Intensity 25 Social Releaser 2o Behaviour Hierarchy 3 0 SUMMARY 3 2 ACKNOWLEDGEMENT S 3 ^ LITERATURE CITED 3 5 i i TABLES Table I . Comparison of the nipping i n t e n s i t y of;coho and trout (Chi square = 390, p = /0.001). ...12 Table I I . Showing the nipping i n t e n s i t y d i s -played by trout i n r e l a t i o n to the same and di f f e r e n t species 15 Table I I I . Effectiveness of models i n e l i c i t -ing a. nipping response when placed i n an aquarium containing 12 trout l6 i i i FIGURES Page Figure 1. Rheostats (water-cooled) placed i n series for increasing or decreasing i l l u m i n a t i o n . A, pointer leading to a calibrated scale; B, wooden bar for operating rheostats sim-ultaneously;- C, rheostat; D, outlet tube f o r c i r c u l a t i n g water; E, e l e c t r i c key. .... 8 Figure 2 . S e t t l i n g of coho when l i g h t i n t e n s i t y decreases. to follow 11 Figure j5. Arithmetic r e l a t i o n s h i p between l i g h t i n t e n s i t y and nipping phenomenon. to follow 11 Figure 4. Relationship between size of t e r r i t o r y held and size -of f i s h . L, large; M, medium; S, small. ......... to follow 12 Figure 3. Nipping relationship i n a heterotypic group of 6 coho and 6 trout. T, trout; C, coho; t o t a l time period of observa-tions, 19 hours and 43 min. ... to follow 13 Figure 6 . Effect of l i g h t i n t e n s i t y on nipping (based on 18 hours observation). rto follow 13 Figure 7 . Increase i n nipping as the l i g h t i n t e n s i t y increases (based on 16 hours observation). to follow 13 Figure 8. Wooden model showing general features of trout (X . 7 ) . to follow . 16 Figure 9. C y l i n d r i c a l wooden model with no d e t a i l (X . 7 ) . . to follow 16 Figure 1 0 . A r t i f i c i a l lure used to duplicate the rhythmical swimming movements of trout (X .7 ) to follow 16 Figure 1 1 . Threatening action of trout. A, twisted caudal portion of the body; B, mouth open and pectoral f i n s extended; C, angular position and twisted trunk. ... to follow 28 Figure 12 . Trout eating alevins to follow 28 Figure 1 3 . Schematic representation'of the behav-iour hierarchy i n trout. ..... to follow 30 INTRODUCTION For centuries man has been observing and, to some extent, recording the actions of animals in their natural habi-tat . For the most part, these observations were not systematic or analytical being promoted by a desire to satisfy Innate curiosi ty . With the advance of biological knowledge the need for more co-ordinated information beoame apparent. To meet this requirement animals were, wherever possible, studied in a laboratory; here, observation d i f f i cu l t i e s are minimized and a r i g i d control more readily maintained. Extrapolation from the laboratory to the f i e ld has been c r i t i c i s e d . It i s questionable, however, whether a better method has as yet been devised. A number of the behaviour patterns of Juvenile coho salmon (Oncorhynchus kisutch) have been described by Hoar (1951). In this Investigation the sett l ing, nipping and t e r r i -t o r i a l behaviour of coho has been explored more thoroughly in relation to l ight intensity and the analysis extended to include kamloops trout underyearllngs (Sstlmo galrdnerl i kamloops). Particular emphasis has been placed on the comparison of v i su-a l l y released behaviour patterns in the two species. Coho and kamloops trout underyearllngs are excellent material for a study of this type as they are readily available 2 and are not v i s i b l y affected by a r t i f i c i a l condi t ions . The l i f e h i s t o r i e s of these two species d i f f e r markedly a f ter the i n i t i a l stages. Coho salmon adults migrate upstream i n the f a l l and spawn during November and December. The adults die a f t e r spawning. The f r y begin to appear In A p r i l and spend up to twelve or more months i n fresh water. The majority m i -grate before the end of t h e i r f i r s t year ( C a r l and Clemens, 1948>). These f i s h return i n t h e i r t h i r d year to complete the c y c l e . In contrast , kamloops trout (referred to i n subsequent paragraphs as " t r o u t 8 ) spawn i n streams short ly a f t e r the ice leaves, usua l ly i n May and June. The exact spawning time v a r i e s i n d i f f e r e n t l o c a l i t i e s . The f r y may remain permanently i n the stream or enter the lake during the f i r s t year. The fo l lowing d e f i n i t i o n s have been used i n the d e s c r i p t i o n of the behaviour of young coho and t r o u t : (a) s e t t l i n g i n which f i s h descend from the upper to the lower l e v e l s of water and become quiescent as the l i g h t i n t e n s i t y i s reduced. (b) nipping " i n which one f i s h makes a guick d a r t i n g move-ment toward, and b i t e s u s u a l l y close to the base of, another f i s h ' s t a i l . The a c t i o n does not Involve any actual contact between f i s h for only the water near the attacked f i s h i s ' b i t t e n ' . The nipped f i s h move© away r a p i d l y . (Hoar, 1 9 5 1 . ) S l i g h t di f ferences i n character n of nipping behaviour i n trout w i l l be described l a t e r . 3 (c) defence of t e r r i t o r y - " i n which a f i s h establishes i t s e l f i n a l o c a l i t y and by nipping keeps other f i s h from t h i s area": (Hoar, 1951). (d) behaviour - a l l the movements of the i n t a c t animal (Tinbergen, 1 9 5 1 ) . (e) innate behaviour - behaviour that has been changed by learning (Tinbergen, 1 9 5 1 ) . (f) drive - "the complex of i n t e r n a l and external states and s t i m u l i leading to a given behaviour'* (Thorpe, 1 9 5 1 ) . (g) appetitive behaviour - "thevvariable introductory phase of an i n s t i n c t i v e behaviour pattern or sequence" (Thorpe, 1 9 5 1 ) . (h) i n s t i n c t - "an inherited and adapted system of coordina-t i o n within the nervous system as a whole, which when activated finds expression i n behav* iour culminating i n a fi x e d action pattern. I t i s organized on a h i e r a r c h i a l basis both on the afferent and efferent sides" (Thorpe, 1 9 5 1 ) , (I) s o c i a l releaser - "any s p e c i f i c feature or complex of features of an organism e l i c i t i n g an a c t i v i t y i n another i n d i v i d u a l either of the same or another species" (Thorpe, 1 9 5 1 ) . (j) learning - "the process which produces adaptive change i n i n d i v i d u a l behaviour as the r e s u l t of experience" (Thorpe, 1 9 5 1 ) . 4 MATERIALS AND METHODS Se t t l i n g Coho underyearllngs s e t t l e toward the bottom and become quiescent during the period of darkness (Hoar, 1951). In order to determine the l i g h t i n t e n s i t y at which these f i s h s e t t l e , twelve were placed i n a tank and observed i n r e l a t i o n to changes i n i l l u m i n a t i o n . The observation was metal (90 cm. high, 65 cm. wide and 50 cm. from back to front) with a heavy plate glass f r o n t . I t was marked off into three compartments (each 30 cm. high.and numbering 1, 2, and 3 from top to bottom). The tank was placed In a corner so natural i l l u m i n a t i o n could f a l l on the surface of the water from windows at the rear and on one side. This corner of the room was screened o f f and another screen placed h o r i z o n t a l l y at the l e v e l of the top of the tank and attach-ed to the v e r t i c a l one. This arrangement prevented l i g h t from entering the glass fron t . An observation chamber was erected and the f i s h observed through a s l i t i n the v e r t i c a l screen. The i n t e r i o r of the tank was coated with p a r a f f i n wax; the bottom was covered with the same material mixed with f i n e p a r t i c l e s of charcoal to reduce r e f l e c t i o n . This resulted i n a gradient of l i g h t i n t e n s i t y . Because of the high r e f l e c t -ing property of wax, counts could be taken at low i n t e n s i t i e s . A "Photovolt Universal Photometer" (Model 2 0 0 ) was used to determine the amount of l i g h t s t r i k i n g the water. The photo-electric c e l l was attached to the top of the tank two inches above the water. Differences between t h i s point and the surface d £ the water were n e g l i g i b l e . The l i g h t meter was operated from the observation chamber and a "pen f l a s h l i g h t " was used to a i d i n reading the scale. Each group of f i s h was held i n the tank for one week and fed i n the morning by tossing i n food from behind the screen. Lights In the room were not used on days when observations were made. The f i s h were watched for period varying from 1 to 1 1 / 2 hours. Darkness was always the time l i m i t i n g factor. The num-ber of f i s h i n compartment 1 and 2 plus the corresponding l i g h t i n t e n s i t y was recorded at 5 minute i n t e r v a l s . For t h i s experiment the temperature range was 7o&°C-9.6°C ' -;• Nipping and T e r r i t o r i a l Defense I n addition to s e t t l i n g , coho and trout show a nipping and t e r r i t o r i a l reaction. These behaviour patterns were studied quan t i t a t i v e l y and q u a l i t a t i v e l y . The effect of a heterotypic group of 6 coho and 6 trout was also studied. An aquarium (lcIO cm. long, l c 5 cm. wide and 2 5 cm. deep) was placed i n a darkroom and observations taken from behind a screen. Movements of the observer were apparently not detected by the f i s h . The depth of water was 1 0 cm. being 6 regulated by an overflow pipe at one end. The i n l e t was at the opposite end. Both i n l e t and o u t l e t were screened o f f , reducing the e f f e c t i v e length to 1^ 0 cm. A carbon f i l t e r ( a d d i t i o n a l dechlor inat ing device) was placed on the end of the aquarium where the water entered. I l l u m i n a t i o n was from a 1 2 0 watt l i g h t d i r e c t l y over and f i v e feet above the tank (10.2 foot candles at the surface) . Twelve f i s h were used i n each group and were a r b i t r a r i l y c l a s s i f i e d as large (6-6.5 cm.), medium (5-5*5 cm.) and small 4-.5 cm.). Lengths of I n d i v i d u a l f i s h were not taken but i n every group four belonged to each s ize range. The two homotypic groups were recorded for IS hours. Records were kept of t o t a l number of n i p s ; the r e l a -t i v e s ize of f i s h nipping and being nipped; and s ize of t e r r i -t o r y , i f any, held by dominant f i s h . The heterotypic groups were observed for 1 9 hours and K$ minutes i n order to compare the Inter and i n t r a s p e c l f i c r e l a t i o n s h i p . Temperature range was 9 ° C . - 1 1 . 7 ° C . L ight Intens i ty The effect of l i g h t i n t e n s i t y on nipping was studied using the same long aquarium and darkroom with a modified l i g h t i n g arrangement. A ser ies of f i v e l i g h t s (60 watts each) was placed above the aquarium. Two rheostats were placed i n the c i r c u i t i n ser ies so the Intens i ty could be Increased or one decreased as desired. The resistance of Arheostat was 2 0 ohms and the other *J4 ohms. The range was from 0 - 1 5 foot candles at the water surface when the l i g h t was passed through frosted glass plates. The l a t t e r gave a more even d i s t r i b u t i o n of il l u m i n a t i o n . The rheostats were operated simultaneously and c a l i -brated by a photometer. An elecJbrlc key was used to break the c i r c u i t (Figure 1 ) . Each group of f i s h was placed i n the aquarium at night and the l i g h t s turned on the following morning. A mini-mum of 6 hours was given f or adaptation to the l i g h t i n g . In studying the effect of decreasing i l l u m i n a t i o n the procedure was as follows: (a) reduce l i g h t s from the maximum ( 1 5 f.c.) to 1 2 f.c. (b) allow 5 minutes f o r adaptation. (c) record nipping f o r 1 0 minutes. (d) reduce l i g h t s and repeat. Observations were taken at 1 2 , g, 6 , 2 . 5 , 1 . 5 , 0 . 7 5 , 0 . 2 5 and 1 2 foot candles respectively. The l a t t e r was a check on the nipping i n t e n s i t y when the i l l u m i n a t i o n was immediately increased. ft The period f or adaptation was eliminated when deter-mining the effect of increasing l i g h t and records were kept f or 1 5 minute i n t e r v a l s . The l i g h t s were increased from O-ty f. c . i n increments of 0 . 5 f.c. I n i t i a l l y i t was Intended to vary Figure 1. Rheostats (water-cooled) placed i n series for increasing or decreasing i l l u m i n a t i o n . A, pointer leading to a calibrated scale; B, wooden bar for operating rheostats sim-ultaneously; C, rheostat; D, outlet tube fo r c i r c u l a t i n g water; E, e l e c t r i c key. 9 the rate of increase and compare the r e s u l t s ; however, because of the v a r i a b i l i t y between groups and i n the same group at d i f -ferent periods, t h i s procedure was abandoned i n favour of a simple l i g h t increase—nipping r e l a t i o n s h i p . Social Releaser What i s responsible:.for nipping? In an attempt to answer t h i s question a number of l i v e f i s h and models were tested with a group of trout. The f i s h used were Black Crappie (Pomoxls nlgro-maculatus LeSueur), Goldfish (Carasslus auratus Linnaeus), Stickleback (Gasterosteus aculeatue Linnaeus), Pea-mouth chub (Mylochellus caurlnus Richardson), Goarse-scaled Sucker (Oatestomus macrochellus Glrard), P r i c k l y Sculpln (Cottus, asper Richardson) and Chum Salmon' alevlns (Oncorhynchus  keta Walbaum). Models were carved from wood and painted a variety of colours. Each was covered with a t h i n coating of p a r a f f i n wax before using. Some were " f i s h l i k e " having the general configuration with mouth and caudal f i n ; others were c y l i n d r i -c a l having no d e f i n i t e shape (Plate I ) . One end of a fine s t e e l wire was passed through the model, the other sealed into a long piece of glass tubing. Models were placed i n the aquarium at low l i g h t i n t e n s i t i e s . This method could not duplicate the rhythmical swimming motion of trout ao a number of a r t i f i c i a l lures were used. The l a t t e r 10 were pulled through the water. Trout without a dorsal, anal, or caudal f i n were also tested. The method was to place 8 small and k large f i s h i n the tank. Of the cl small ones, k had one of the above mentioned f i n s clipped o f f . Only the nipping of the four large members was recorded. In addition to models and l i v e f i s h , dead trout were used. Some were mounted on pins and placed i n the tank; others were suspended on a wire by passing I t through the long axis of the body and moved i n the same way as the wooden models. 11 RESULTS Se t t l i n g The r e s u l t s of s e t t l i n g observations are shown graphically i n Figures 2 and 3. Figure 2 demonstrates the semi-logarithmic r e l a t i o n s h i p . The calculated regression co-e f f i c i e n t of the l i n e i s -g,c4 and the 95% confidence l i m i t s -5,15 and -10,93, This i s s i g n i f i c a n t at the p=.01 l e v e l ("t" tables). Figure 3 i s an arithmetic graph and serves to i l l u s t r a t e the natural trend. At high l i g h t i n t e n s i t i e s there i s a tendency for f i s h to inhabit the upper regions of the tank. As l i g h t decreases they gradually s e t t l e . The apparent c r i t i c a l inten-s i t y (Figure 3) f o r t h i s behaviour i s approximately 1 foot candle and below t h i s there i s a marked increase i n numbers at or near the bottom. From Figure 3 t n e percent of f i s h i n the two upper compartments decreases from 59»3# * ° 3^»2# bet-ween 0.75 and 0.25 f.c. (mid-points) respectively. There i s a c e r t a i n amount of v a r i a b i l i t y due pr i m a r i l y to t e r r i t o r i a l defense; a factor that w i l l be dealt with l a t e r . —I 1 1 1 1 1 1 1 1 1 1 — .25 .75 1 25 I.7S 2.25 2.75 3.25 3.75 4.2S 4.75 5 + MID POINTS OF LIGHT INTENSITY (FOOT CANDLES) Figure 2. S e t t l i n g of coho when l i g h t Intensity decreases!. Figure 3« A r i t h m e t i c r e l a t i o n s h i p between l i g h t i n t e n s i t y and sett//Tig r: • ; ' ' IE Nipping and T e r r i t o r i a l Defence The r e s u l t s of the quantitative nipping are seen i n Table I . Coho nip more frequently than trout inthe r a t i o of 2814:1514. In both species size i s a facter influencing the f i n a l consummatory act of nipping. A consummatory act i s a sp e c i f i c stereotyped set of movements e l i c i t e d by an innate releasing mechanism involving a simple motor response such as b i t i n g or nipping (Craig, 1918; Tinbergen, 1950). Table I . Comparison of the nipping i n t e n s i t y of coho and trout (Chi square - 390, p - /.001). Species Observation Number of (hours) Nips Coho 18 3,814 Trout 18 1,514 Not only do the f i s h nip but the dominant member or members of a group frequently display t e r r i t o r i a l behaviour i n that these f i s h w i l l e s t a b l i s h themselves i n an area and* drive other members out by employing nipping and/or chasing t a c t i c s (Hoar, 1951). The re l a t i o n s h i p between size of t e r r i t o r y and size of f i s h can between i n Figure 4. A large coho held 44.4% on the average while the,, small members held 26.4%. The s « o M o u K 50 40 -30 20 C TROUT 00 CO Figure 4. Relationship between size of t e r r i t o r y held and size of f i s h . L, large; M, medium; S, small. 1 13 calculated " t " value i s 2.45 f o r 13 d.f. which, i s s i g n i f i c a n t at the 0.05 p r o b a b i l i t y l e v e l ("t" t a b l e s ) . For trout the large dominant members held 46.9% and the small t r o u t l 6 . 7 % . The c a l c u l -ated " t " value i s 5.18 and f o r 8 d.f. i s s i g n i f i c a n t at the 0.01 pr o b a b i l i t y l e v e l . lAftien a homotypic group i s replaced by a heterotypic one the re s u l t s are reversed(Figure)5)• Trout are more dominant "nippers" i n the r a t i o of 1619:601. I t i s of int e r e s t to note that the 6 trout i n t h i s group nipped almost as often as the group of 12. Reducing the results of the heterotypic to an equivalent time i n t e r v a l , the figures are 1514:1475. There i s no significance between the r e s u l t s . Trout show no preference between members of there species and coho while the l a t t e r nip trout less frequ-ently (337:264, Chi square s 8.867 and p « / 0.01). I t soon became evident that the nipping a c t i v i t y of coho was depressed by the presence of trout. To test t h i s , trout were removed from group 5 and observations taken f o r a l i k e period of time (2 hours). When trout were present the t o t a l coho nipping was 19; when the former were removed the t o t a l equalled 64. The Chi square value i s 24.1 which i s highly s i g n i f i c a n t . Light Intensity The effectiveness of l i g h t as a l i m i t i n g factor on the nipping response can be seen i n Figures 6 and 7. There i s no general decrease (Figure 6) u n t i l the i n t e n s i t y has been reduced to 4 f . c . and below t h i s value the decline i s rapid. - • I Figure 5* Nipping relationship i n a heterotypic group of 6 coho and 6 trout. T, trout; C, coho; t o t a l time period of observa-tions, 19 hours and 45 minutes. " I 1 1 1 1 1 1 1 1 1 1 1 1 r~ 12 10 8 6 4 2 0 IZ LIGHT INTENSITY ( F O O T C A N D L E S ) F i g u r e 6. E f f e c t o f l i g h t i n t e n s i t y on n i p p i n g (based on 18> hours o b s e r v a t i o n ) . 3 0 0 •5 I 1-5 2 2-5 3 3-5 4 LIGHT INTENSITY (FOOT CANDLES) Figure 7. Increase i n nipping as the l i g h t i n t e n s i t y increases (based on l 6 hours observations). 14 The dotted l i n e represents the number of nips when the inten-s i t y i s immediately increased to 12 f.c. The l a t t e r i l l u s t r a t e s quite conclusively that the diminishing l i g h t i n t e n s i t y was responsible f or the drop i n nipping. Figure 7 d i f f e r s from Figure 6 i n that the l i g h t i s increasing. Nipping increases slowly at f i r s t and then r a p i d l y . The point of I n f l e c t i o n f o r the curve i s between 2 and 2.5 f . c ; above t h i s there i s a deceleration and a l e v e l l i n g at 4 f.c. In e f f e c t , the two graphs are complementary. Soci a l Releaser Table I I and I I I summarize the investigation of fac-tors responsible for nipping. Neither dorsal, caudal or anal f i n i s the releaser since f i s h mutilated i n t h i s way are nipped as frequently as uninjured ones. Peamouth chub and small suckers are nipped r e a d i l y ; however crapples, stickleback, g o l d f i s h , sculpins and tadpoles.are not. Alevlns were eaten. In general, models were not as e f f e c t i v e as l i v e f i s h but a l l , except the orange-coloured one, e l i c i t e d at least one response. Table I I . Showing the nipping int e n s i t y displayed by trout i n r e l a t i o n to the same and d i f f e r e n t specie s . Species Number Size (cm.) Time of Number of nips observation (hours) Calico bass 5 4.5-5 2 12 Stickleback 5 " 5-6 2 16 P r i c k l y sculpin 4 4.5-6.5 2 21 Peamouth chub 6 5-6 2 71 Sucker 5 3.5-4.5 , 2 67 Goldfish (gp. 1) 3 7-7.5 2 1 Goldfish (gp. 2) 2 5-5.2 2 •0 Goldfish (gp. 3), 3.8-4.S 2 0 Trout without anal 4 4.5-5.5 2 46 Trout without caudal 4 4.5-5.5 2 51 Trout without dorsal 4 4.5-5.5 2 3* Alevlns (O.gorbuscha) 2 2 eaten Coho 6 4.5-5.5 2 163 Table I I I . Effectiveness of models response when placed i n (4 - 6 cm. i n length) i n an aquarium containing e l i c i t i n g a nipping 12 trout. Model Number Time of observation (hours) Number of nips Red 1 2 1 Orange 1 2 0 Green 1 2 11 Blue 1 2 14 Brown 1 2 17 Black 1 2 8 Yellow 1 2 White .; 1 ' Trout on pin 1 2 2 2 0 Trout on wire 1 2 29 I was not moved P l a t e I F i g u r e 9 . C y l i n d r i c a l w o o d e n m o d e l w i t h n o d e t a i l ( X . 7 ) . F i g u r e 1 0 . A r t i f i c i a l l u r e u s e d t o d u p l i c a t e t h e r h y t h m i c a l s w i m m i n g m o v e m e n t s o f t r o u t ( X . 7 ) . 1 7 DISCUSSION S e t t l i n g The aquarium was not e n t i r e l y s a t i s f a c t o r y f o r determining the l i g h t i n t e n s i t y at which f i s h w i l l s e t t l e toward the bottom because of t h e i r t e r r i t o r i a l habits. In 9 of the 1 7 observations one of the dominant members selected the lower compartment and drove the others upward as they entered t h i s area. Figure 3 would indicate a c r i t i c a l value approximately 1 f.c. for t h i s response; however, Figure 6 demonstrates a marked decrease i n nipping at t h i s value. Since t e r r i t o r i e s are defended by nipping (Hoar, 1951)» de-fense of an area must be less e f f i c i e n t when i l l u m i n a t i o n i s low. What appears to be a c r i t i c a l value f o r s e t t l i n g may, i n a c t u a l i t y , be the re s u l t of a loss of dominance. The correct c r i t i c a l i n t e n s i t y f or s e t t l i n g could be somewhat higher, say 2 or 3 f.c, A number of observations suggested the l a t t e r to be the case. A larger tank and a smaller num-ber of f i s h would reduce s p a t i a l competition and c l a r i f y t h i s point. I t i s w e l l known that l i g h t Is absorbed as i t passes through water. Because of t h i s i t would be expected that, i f there Is a c r i t i c a l stimulus for s e t t l i n g , the f i s h IS i n the centre compartment would move toward the bottom before those i n the upper. Tota l ing the numbers i n these two sections at and below 2 f . c . the f igures are 3S7:36l (Chi square = O.903S and p s 0 . 5 - 0 . 3 ) . The t h e o r e t i c a l l i g h t i n t e n s i t y entering the centre compartment can be ca lcu lated by using the formula l / l 0 = e ~ k l , where I i s the r e s u l t i n g i n t e n s i t y ; I 0 i s the i n i t i a l i n t e n s i t y s t r i k i n g the surface; e i s 2.7; k i s the c o e f f i c i e n t of absorption and 1 the distance i n meters (Clarke, 1939). The absorption c o e f f i c i e n t s f o r d i s t i l l e d water were used. This introduces a c e r t a i n error but the water was passed through an ac t ivated carbon dechlor inator before entering the tank which would remove suspended m a t e r i a l , thereby reducing the error i n v o l v e d . The absorption c o e f f i c i e n t s were taken from Sverdrup, Johnson and Fleming (1942) and ares ( l ) ' u l t r a v i o l e t ( w . l , 0.39 microns) - 0.14S ( i i ) red ( w . l . 0.6 microns) = 0.21 ( i i i ) beyond red ( w . l . O.S microns) = 2.14 When the l i g h t s t r i k i n g the surface i s 1.5 f . c . the u l t r a v i o l e t and red l i g h t entering the centre compartment i s 1.42 and 1.4 f . c . r e s p e c t i v e l y . For wave lengths O.g microns only 0.75 f . c . enter t h i s area. Wave lengths greater than t h i s are almost t o t a l l y absorbed i n the f i r s t few centimetres. Although the a c t u a l v i s u a l f i e l d i s ' not known, i t has been establ ished that f i s h are sens i t ive to the v i o l e t -red p o r t i o n of the spectrum (Walls , 1942). I f the s e t t l i n g stimulus i s w i t h i n t h i s range we would not necessar i ly expect 1 9 fewer f i s h i n the centre compartment when differences i n l i g h t Intensity are so small. N i p p i n g Coho nip more frequently but l e s s ferociously than trout. On the other hand, r e t a l i a t i o n s by the l a t t e r are more common. In addition, trout show a c h a r a c t e r i s t i c f i g h t i n g behaviour i n that two members w i l l swim i n a c i r c l e seemingly s t r i v i n g for a favourable p o s i t i o n from which to attack the opponent. Associated with f i g h t i n g i s a threat response char-acterized by extension of f i n s * e s p e c i a l l y the pectorals; a twisting of the caudal region of the trunk toward the opponent; Jerky swimming movements; mouth open; and an angular p o s i t i o n i n space. These f i g h t i n g and "threatening™ behaviour patterns have not been previously described for trout (Figure 1 1 ) . The nipping rate i s not constant but w i l l vary greatly i n a one hour period even though l i g h t and temperature are unaltered. As w i l l be discussed l a t e r , the stimulus i s present but the response i s not forthcoming. The same stimulus that releases a maximal reaction at one time may have no e f f e c t or e l i c i t a weak response at another. Such v a r i a t i o n i n thre-shold may be due to v a r i a t i o n i n Intensity of some external or i n t e r n a l factor not controlled i n the experiment (Tinbergen, 1 9 5 1 ) . Lorenz ( 1 9 5 0 ) presents a somewhat d i f f e r e n t explanation. "... the a c t i v i t y i s exhaustible independently from the general 2 0 state of exhaustion of the organism as a whole ..." ( p .2 5 2 ) . "When we suddenly deprive an animal of the object of i t s r e -action, the a c t i v i t y never breaks off abruptly but nearly always continues a considerable time i n vacuo. Doubtless i t i s a consequence of the same phenomenon that the 'momentum' gained by any a c t i v i t y w i l l carry i t on for an appreciable time a f t e r the moment when i t s releasing threshold, r i s i n g con-t i n u a l l y throughout the duration of the discharge, has reached the value corresponding to the external stimulation impinging at the moment. This i s also the reason why an organism that i s l e f t continually i n the presence of a releasing object does not continually react to i t with a constant i n t e n s i t y , as other-wise would be expected" ( I b i d . , p , 2 5 9 ) . I t seems plausible that exhaustion of the s p e c i f i c a c t i v i t y , r i s e i n threshold and a d i v e r t i n g Influence of external and i n t e r n a l changes are fac-tors Responsible for v a r i a t i o n i n the nipping rate. I t has been shown that there i s a decline i n frequency of nervous im-pulses with constant stimulation (Adrian and Matthews, 1 9 2 7 ) . This decline i n discharge may be synonymous with increase i n threshold and account for the exhaustion of a s p e c i f i c a c t i v i t y . Quiescence follows a period of r e l a t i v e l y vigorous nipping. Associated with t h i s i s a decline In threshold value and a r e p e t i t i o n of events providing some d i v e r t i n g or i n h i b i t -ing factor i s not present. The longer a stimulation i s withheld the f i n e r the trig g e r releasing i t becomes and may ac t u a l l y reach zero with the reaction taking place i n the absence of a 21 stimulus. This vacuum effect i s termed "energy accumulation a c t i v i t y " (Armstrong, 1942). Stating the phenomena i n terms of t h i s experi-ment, a "macro" stimulus i s often necessary to i n i t i a t e nip-ping; however, once started the "nipper" may chase the other the length of the tank a number of times or nip other members i n the v i c i n i t y with Increased vigor u n t i l the point of exhaust-ion for t h i s s p e c i f i c act i s reached. Occasionally t h i s takes place without any or with a weak v i s u a l stimulus (to the obser-ver) and t h i s i s c a l l e d "energy accumulation a c t i v i t y " . The behaviour of animals tends to follow stereo-typed patterns of movement and once f a m i l i a r with these an ob-server can predict with reasonable accuracy what to expect from the organism (Lorenz, 1950). An example of t h i s i s the "threat" reaction and a number of nips following. Reference has been made to d i v e r t i n g factors. The most important and ever present one was the aquarium i t s e l f . Should the f i s h come i n contact with the glass sides or the screen at either end the behaviour breaks o f f at t h i s point and may not resume for many minutes. A reduction of l i g h t and s l i g h t movement of the screen act i n a s i m i l a r manner! Because of t h i s , i t i s possible to t e l l , w ithin l i m i t s , where and when nipping w i l l take place. In a heterotypic group 6 trout nipped as f r e -quently as 12 i n a homotypic group. The more probable explana-t i o n i s based on the d i f f e r e n t i a l nipping i n t e n s i t y . Rarely do the 6 more dominant members i n a group of 12 nip less than 9 0 2 2 percent of the t o t a l and In some Instances one Individual may perform 9 5 percent. I t i s apparent from the conduct of the trout that they were the dominating species and, since there i s no nipping preference shown by then (Figure 5 ) » "the. r e s u l t s are not greatly out of l i n e with the others. A d i f f e r e n t i a l nipping i n t e n s i t y between members of a group i s common i n both species. Vsing the same argument as above i t might be concluded that 6 coho would nip as often as 1 2 providing there i s nothing acting to r e s t r a i n t h i s a c t i v i t y . But coho nip coho more than trout and the Intensity i s accelerated by the removal of the l a t t e r . The presence of one species sup-pressing the a c t i v i t y of another i s not uncommon. I t has been demonstrated that g o l d f i s h become more active as f a r as t o t a l movement i s concerned when grouped with other f i s h (Escobar, Mlnahan and Shaw, 1 9 3 & ) . In other words the presence of the others modified the behaviour of the gol d f i s h . Dr. W. S. Hoar (Professor, University of B r i t i s h Columbia) carried out preliminary experiments on the int e r a c t i o n of coho and kamloops trout. His r e s u l t s , although not as ex-tensive as these, indicated the reverse to be true. Immediately the question a r i s e s , what i s the effect of environment, condition-ing, age, r a c i a l differences ( i f any), etc., on the actions of f i s h i n t h i s or v any other type of behaviour study. Knowledge of f i s h has Increased greatly i n the l a s t half century but the rela t i o n s h i p of the above mentioned factors as modifying beha-viour i s not c l e a r l y understood. Dr. Hoar's f i s h were "wild" 2 3 f i s h tested Immediately a f t e r capture. The trout used by the writer were reared i n a hatchery but the coho were taken from a stream. Both species were retained separately at the Univer-s i t y for two months p r i o r to grouping them i n an aquarium, but previous conditioning may have had an e f f e c t , remote as the pos-s i b i l i t y may seem. I f some or a l l of the points mentioned a l t e r the general behaviour of an organism, much of the present i n f o r -mation, e s p e c i a l l y that concerning animal ethology, i s , at best, a guide u n t i l i t has been duplicated under a d i f f e r e n t , although comparable set of conditions. It i s not known what i s responsible i n determining whether a f i s h w i l l or w i l l not become, the dominant member and/or show t e r r i t o r i a l defense. Hoar ( 1 9 5 1 ) nas noted that dominant members are often brighter i n colour. This suggests a hormonal basis. Colouration i n regard to nipping and dominance i s questionable but the general state of h^Lth i s important. Coho and trout underyearlings commence nipping a few hours a f t e r placing them i n a tank. In December, 1 9 5 1 * coho were observed for 10 days without t h i s behaviour being seen. The f i s h v i s i b l y appeared i n poor condition. It was determined that the water supply was responsible for t h i s because of an excess of c h l o r -inated water passing thrbugh the deohlorinatlng u n i t . As the volume of water increased the e f f i c i e n c y of the l a t t e r decreased. Because of the stress placed on the organism by toxic materials, 2 4 possibly chloramine, which i s l e t h a l to small trout at 0.05 p.p.m. (Coventry, Shelford and M i l l e r , 1935.)» nipping stopped. A l l f i s h were dead two weeks l a t e r . Eventually an ad d i t i o n a l carbon f i l t e r was used to r e c t i f y the si t u a t i o n . Some of the e a r l i e r work was discarded i n order to eliminate possible biased r e s u l t s . Nipping r e f l e c t s the phy s i o l o g i c a l condition of coho and trout but whether an empirical r e l a t i o n s h i p exists may be ascertained by further study. Preliminary tests were made by observing trout i n contaminated water. Nipping did not occur. Because of the l i m i t e d number of observations, the r e s u l t s can not be considered conclusive. Coho were not available i n a num-ber of streams at t h i s time of year. There Is no "nip" order similar to the "peck" order i n some birds for at one moment "A" w i l l be nipping and chasing "B" but l a t e r the s i t u a t i o n may be reversed. I f "A" i s larger than "B" the former w i l l chase and nip more frequently* Repre-senting t h i s i n equation form we would have "A" - y ^  "B". Simi-l a r i l y , large f i s h w i l l defend larger t e r r i t o r i e s (Figure 4 ) and there i s l e s s p r o b a b i l i t y of them being displaced by another mem-ber. Large trout displayed t e r r i t o r i a l defense on 1 3 of 1 9 occa-sions; t h i s was recorded twice for small trout. 25 Light Intensity Like s i z e , l i g h t i n t e n s i t y affects the general nipping phenomenon below I n t e n s i t i e s of 4 f.c. From t h i s point to 0 f.c. there i s a rapid decline i n a c t i v i t y , There- i s good evidence to suppose that at 0 f.c. nipping does not.take place (Figure 5 ) . No l i t e r a t u r e has been found comparing the sensi-t i v i t y of the f i s h eye to the same stimulus when the quantity of l i g h t i s varied. But i t seems evident that a f i s h can not see as w e l l at 1 f.c. as at 1 0 . A number of workers have intimated t h i s but a pertinent reference i s not c i t e d . Walls (1942) states? " A l l i n a l l , i f a f i s h or whale can d i s t i n g u i s h objects f i f t y feet away at his own l e v e l , I t i s a r e d - l e t t e r day for him. With increasing depth or Increased t u r b i d i t y , t h i s distance i s s t i l l further reduced since the absolute amount of l i g h t r e f l e c t e d Into the eye of the animal de-pends upon the r e l a t i v e amount of sunlight reach-ing that depth." ( p p . 3 7 5 - 3 7 6 . ) Rochon-Duvlgneaud and Roule ( 1 9 2 7 ) have demonstrated that the sharpness of v i s i o n i n Salmo and Esox i s considerably reduced below that of man and other t e r r e s t r i a l vertebrates. The w r i t e r noted that trout could not detect movements of the observer when ill u m i n a t i o n was reduced. The q u a l i t y of a r t i f i c i a l white l i g h t changes as i t i s reduced and the gradual cessation of nipping may be related to the elimination of some component rather than the general re-duction. At low i n t e n s i t i e s there i s an increased percent of 2 6 orange-red portion of the spectrum. Also, orange and red models were least effective In e l i c i t i n g a response. Kowamoto and Takedo ( 1 9 5 1 ) carried out a series of experiments on the wave length preference of s i x species: Oplegnathus fa c l a t u s, Monacanthus c l r r h l f e r , Cyblumr nlphonlum, Shyraena Japonlca, Shyraena nlphobles and Angullla Japonlca. A l l species except A. Japonlca preferred the blue-green wave lengths and avoided red and v i o l e t . They determined the energies f o r d i f f e r e n t colours and found v i o l e t and red to be extremely high while blue and green were low. E a r l i e r work by Reeves ( 1 9 1 9 ) shows that g o l d f i s h and horned dace (Semotilus atromaculatus) w i l l go to blue i n preference to red l i g h t but when the " i n t e n s i t y " of red l i g h t i s equivalent to blue (for human eye) the f i s h f a i l to discriminate between them. Reeves does not indicate whether in t e n s i t y refers to:energy or:.a ^ photometric reading. I f energy i s referred to the work of Kowamota and Takedo substantiates t h i s ; however, i f a photometric reading of Intensity i s meant, the evidence i s contradictory. An experiment using coloured f i l t e r s would help confirm the effect of wave length on nipping. Social Releaser The s o c i a l releaser for nipping i s movement which must release a series of in t e r n a l processes i n the nervour sy-stem, the exact nature of which i s not known (Tinbergen, 19*4-2). 2 7 This was arrived at by a process of elimination. When the chub were nipped the p o s s i b i l i t y of parr marks and a s p e c i f i c swim-ming rhythm was ruled out. Suckling and Suckling (1950) state that the swimming of d i f f e r e n t species cause a di f f e r e n t e l e c t -r i c a l response i n the l a t e r a l l i n e system. Various f i n s were removed but the re s u l t s were negative. When dead trout and models were used they were nipped only when moved. Crappies, stickleback, sculpins, g o l d f i s h and tadpoles do not provide the releaser stimulus as often as chub, suckers and other Salmonolds. Stickleback and crappies change s p a t i a l p o s i t i o n by sudden darting movements and then remain motionless f o r variable periods. When nipped they move away rapidly and are usually chased and nipped again. This indicates, as c e r t a i n l y seems to be the case, that the darting motion i s sub-limlnal i n i n t e n s i t y and only e f f e c t i v e when a trout i s situated i n the near proximity and the accumulative effect of many inadequate s t i m u l i reach the threshold and eventually pro-duce a response. Sculpins and tadpoles do not perform darting movements but remain motionless on the bottom changing p o s i t i o n infrequently. They are nipped only when i n motion. Coho, trout, chub and suckers are nipped equally. These f i s h have a rhyth-mical type of movement and do not remain i n one po s i t i o n f o r long i n t e r v a l s . Goldfish were nipped once i n si x hours of obser-vation even though they are active and movements rhythmical. 2S Size did not make any difference. From the previous discussion on l i g h t and from the information obtained using models, the colouration i s probably responsible for t h i s . I t i s not that g o l d f i s h do not stimulate the nipping response i t s e l f but rather the f i n a l consummatory act i s i n h i b i t e d . . To c l a r i f y t h i s the behaviour w i l l be outlined. A g o l d f i s h moves near a trout and the l a t t e r may dart toward i t showing a l l the indications that i t w i l l nip. At the l a s t moment i t w i l l veer to one side and not complete the s p e c i f i c act. It i s suggested that the orange colour i s the i n h i b i t i n g element. Alevlns are not merely nipped, they are eaten (Figure 12). I t has not been determined whether or not the i n i t i a l attack i s or i s not the same as that involving nipping. However, one point i s c l e a r l y i l l u s t r a t e d that age and/or size of a f i s h i s not important i n determining when i t becomes p i s c -ivorous but only the predator-prey size r e l a t i o n s h i p . Models were much less e f f e c t i v e than some l i v e f i s h and, even though the attacks came as far as actual b i t i n g , they were never as intense as when l i v e specimens were used. The models were moved i n a straight l i n e through the water and t h i s i s a t y p i c a l of the l i v e f i s h . Also, i t was impossible to duplicate the "threat" reaction shown by trout and to a l e s s e r extent by coho. The presence of the wire and glass rod from which the models were suspended c e r t a i n l y detracted from t h e i r effectiveness. Morphological features such as form, iridescence of body and pigmentation probably have an additive value i n Plate I I . Figure 11, Threatening action of trout. A, twisted caudal portion of the body; B, mouth open and pectoral f i n s extended; C, angular p o s i t i o n and twisted trunk. Figure 12. Trout eating alevins 2 9 releasing a response. Pelkwijk and Tinbergen ( 1 9 3 7 ) found t h i s to be true when models vete used to e l i c i t a response from stickleback. Movement as an attack releaser i s known to occur i n other f i s h , namely barracuda (Shyraena barracuda) and some sharks (Wright, 194g). The sharks considered dangerous are the Brown (Carcharinus galeolamna), Tiger (Galeocerdo a r c t l c u s ) , Hammerhead (Sphyrna sp.), and the Great White (Carcharodon sp.). Wright spent two and a half years t r a i n i n g the B r i t i s h Sea Reconnaissance Unit i n underwater work off the coasts of C a l i f o r -n i a , Bahamas, Ceylon and Burma. During t h i s time the actions of these f i s h were recorded and h i s conclusions are that blood i n the water acts as a stimulus to lower the threshold value of the attack response and causes e x c i t a b i l i t y . Rapid and/or Jerky movements are also necessary i n releasing attack. The presence of blood and Jerky or f r a n t i c movements result i n the strongest attack. Movement i s the actual releaser and w i l l e l i c i t attack alone but blood has an accumulative effect i n hastening and strengthening the response. Trout w i l l nip tadpoles, which are amphibians, and wooden models which are not even a good approximation of a f i s h . I t seems u n l i k e l y that tadpoles and models have the same releasing value as trout. "The occurrence of such 'errors 1 or'mistakes' Is one of the most conspicuous c h a r a c t e r i s t i c s of innate behaviour. I t i s caused by the fact that an animal responds ' b l i n d l y ' to only part of the t o t a l environ-^ mental s i t u a t i o n and neglects other parts, although i t s sense organs are p e r f e c t l y able to receive them (and probably do receive them),..." (Tinbergen, 1 9 5 1 * p . 2 7 ) . 3 0 Indeed, such, errors are not r e s t r i c t e d to f i s h . The predacepus water beetle (Dytlecus marginal!s) can be trained to v i s u a l response but the search for food can be stimulated by a watery meat extract. The hunting behaviour i s released by chemical stimulation (Tinbergen, 1 9 3 6 ) . Newly hatched herring g u l l (Larsus a. argentatus Pont) peck at the beak of the parent when hungry. Tlie red patch on the b i l l was of great importance as a s o c i a l releaser but the colour of the beak or head had no releas-ing value ^Tinbergen and Perdeck, 19.50).. "The animal's sensory world i s dependent on sign s t i m u l i especially when we are deal-ing with innate behaviour" (Tinbergen, 1951» p.^ 2 ) . Behaviour Hierarchy The hierarchy of behaviour as shown by Tinbergen ( 1 9 ^ 2 , 19^0% 1 9 5 0 ) i s , to some extent displayed by the trout and to a lesser extent by coho. The highest l e v e l of the hierarchy, the drive, has not been determined. Below the drive l e v e l i s appetitive behaviour which would coincide with the rapid dart toward another f i s h . A second l e v e l of appetitive behaviour would be "threatening" or chasing depending on whether or not the other f l e e s . F i n a l l y , the motor response of nipping which i s the lowest l e v e l of the hierarchy (Figure 1 3 ) . There may be two separate releasers involved i n chasing terminating i n d i f f e r e n t behaviour patterns. When an F i g u r e 1 3 . Schematic r e p r e s e n t a t i o n o f the behaviour h i e r a r c h y i n t r o u t . 3 1 intruder enters a defended area i t may be chased and nipped vigorously by the defender, an a c t i v i t y not r e s t r i c t e d to the defended zone. The. alternative i s that the. dominant f i s h swims toward the intruder, d r i v i n g i t out but does not follow beyond the t e r r i t o r i a l boundary. No attempt i s made to nip the " t r e s -passer" by the f i s h holding the t e r r i t o r y . I t i s d i f f i c u l t to J u s t i f y the preference to nip smaller members on inherent q u a l i t i e s . What, i f any, i s the role played by learning i n t h i s respect? Insight learning i s , according to Thorpe ( 1 9 5 0 ) , the response to simple external s t i m u l i based on the perception of r e l a t i o n s and i s nothing more than form perception having i t s counterpart i n a l l the sensory f i e l d s . Possibly t h i s nipping preference displayed by trout and coho i s not innate behaviour but i s learned shortly aft;er the nipping phenomenon f i r s t occurs. Observations of coho or trout from hatching to two or three months may c l a r i f y t h i s point. 32 SUMMARY 1. Coho underyearllngs s e t t l e to the bottom as the l i g h t i n t e n -s i t y decreases. The c r i t i c a l i n t e n s i t y for t h i s was found to be approximately 1 foot candle but may be higher i n a, stream where competition for space i n a v e r t i c a l d i r e c t i o n i s n e g l i g i b l e . ?.. Coho nip more frequently than kamloops trout. However, i n a heterotypic group of equal numbers trout are dominant and nip either species with equal i n t e n s i t y . The presence of trout i n an aquarium decreases the nipping a c t i v i t y of coho. 3. Nipping i s dependent upon l i g h t and below 4 foot candles decreases rapidly as the l i g h t Is reduced. 4. Limiting factors on nipping are health, size and colour. Coho and trout w i l l not nip i f i n an unfavourable physiolo-g i c a l condition. There i s a tendency for larger members to nip the smaller. Red and orange models and g o l d f i s h were least e f f e c t i v e i n e l i c i t i n g a response. The l a t t e r were nipped only once i n s i x hours of observation. I t i s con-cluded that the prerequisite for nipping i s movement but size and colour are e s s e n t i a l components. Red and orange colour and large size have an I n h i b i t i n g e f f e c t . 3 3 A comparison of the behaviour of coho and trout underyear-l i n g s has been made. Additional patterns are described for trout, namely the "threat" and f i g h t i n g behaviour. 34 ACK_TOWLEDG-EMENTS The w r i t e r wishes to thank Dr. W. A. Clemens, Head, Department of Zoology, University of B r i t i s h Columbia, f o r permission to work on the problem, generous assistance and valuable c r i t i c i s m . Special thanks goes to Dr. W. S. Hoar, Professor, Department of Zoology, f o r selecting the problem, c r i t i c i s m and continual guidance; and to Dr. J . R. Adams, Professor, Department of Zoology, f o r suggestion of a t i t l e . I am indebted to the B r i t i s h Columbia Game Department and espe c i a l l y Cultus Lake hatchery o f f i c e r Frank P e l l s f o r supplying the trout. Most of a l l , the writer would l i k e to express appreciation to his wife, Evelyn, for encouragement and sacri^* f i c e s during u n i v e r s i t y t r a i n i n g . 3 5 LITERATURE CITED Adrian, E. D. and Rt Matthews, 1 9 2 7 . Action of l i g h t on the eye. Jour. Physiol., 6J, 37S-414. Armstrong, E. A., 1942. Bird Display. Cambridge University Press. (Not read but taken from Lorenz, 1 9 5 0 / • C a r l , G. C. and W. A. Clemens, ISkS. The Fresh-water Fishes of B r i t i s h Columbia. King's P r i n t e r , V i c t o r i a , B. C. Clarke, G. L., 1 9 3 9 . The u t i l i z a t i o n of solar energy by aquatic organisms. Problems of Lake Biology, No.10, 2 7 - 3 ^ . Coventry, F. L., V. E. Shelford and L. F. M i l l e r , 1 9 3 5 * The conditioning of chloramine treated water supply for b i o l o g i c a l purposes. Ecol., 1 6 , 6 0 - 6 6 . . Craig, W,, 1 9 1 3 . Appetitles and aversions as.constituents of I n s t i n c t s . B i o l . B u l l . , 9 1 - 1 0 7 . Escobar, R. A., R. P. Mlnahan and R. J . Shaw, 1 9 3 6 . M o t i l i t y factors i n mass (physiology: locomotor a c t i v i t y of fishes under conditions of i s o l a t i o n , homotypic grouping, and heterotypic grouping. Physiol. Zool., ]?, 6 6 - 7 8 . Hoar, W. S., 1 9 5 1 . The behaviour of chum, pink and coho salmon i n r e l a t i o n to t h e i r seaward migration. Jour. Fish. Res. Bd. Can., g, 241-263. Kowamoto, N. and M. Takedo, 1 9 5 1 . The influence of wave lengths of l i g h t on the behaviour of young marine f i s h . P refectural Univ. of Mle, 1 , 41-53. Lorenz, K. Z., 19.50. The comparative method i n studying innate behaviour patterns. Soc. Exp. B i o l . Symposia, No. 4, 2 2 1 - 2 6 3 . Pelkwijk, J . J . Ter, and N. Tinbergen, 1 9 3 7 . Eine relzbiologlsche analyse einiger verhaltensweisen von Gasterosteus  aculeatus. Ze i t . Tierpsychol., 1 , 193-204. Reeves, C. D., 1 9 1 9 . Discrimination of l i g h t of d i f f e r e n t wave-lengths by f i s h . Behav. Mono., No.19, 1 - 1 0 6 . 36 Rochon-Duvigneaud, A. and L. Roule, 1927, Observations sur l e comportement v l s u e l et l a structure de l ' o e i l chez Blennlus b a s l l l c u s . B u l l . Mus. Nation. H i s t . Nat., 2, 139-1M-5. (Taken from B i o l o g i c a l Abstr.) Snedecor, G. W., 19^6. S t a t i s t i c a l Methods. Iowa State College Press, Ames, (^th ed.). Sverdrup, H. V., M. W, Johnson and R. H. Fleming, 19^2. The Oceans. New York, Prentice-Hall, Inc. ' Tinbergen, N., 1936, Eenvorldige proeven over de zintuigfuncties van larvae en imago van de geelgerande watertor. De Levende Nature, £1, 225-236. (Not read but taken from Tinbergen, 1951). , 19*1-2. An o b j e c t l v l s t i c study of the innate be-haviour of animals. B i b l i o t h . blotheor., 1, 39-93. -.: , lO/lfg. Social releasers and the experimental method required f o r t h e i r study. Wilson B u l l e t i n , 60, 6-52. — . 9 1950. The h i e r a r c h i c a l organization of nervous. mechanisms underlying i n s t i n c t i v e behaviour. Soc. Exp. B i o l . Symposia, No.If, 305-336. and A. C. Perdeck, 1950. On the stimulus s i t u a t i o n releasing the begging response i n the newly hatched Herring G u l l chick. (Larsus a. argentatus Pont.). Behaviour, 2, 1-38.. 1951. The Study of In s t i n c t . Clarendon Press, Oxford. Thorpe, W. H., 1950. The concepts.of learning and t h e i r r e l a t i o n to those of i n s t i n c t . Soc. Exp. B i o l . Symposia, No. k, 3S7-ifOg. . 1 1951. The d e f i n i t i o n of some terms used i n animal behaviour studies. B u l l . Animal Behaviour, 1, jk~k-0. Walls, G. L., 194-2. The Vertebrate Eye and i t s Adaptive Radiation. Cranbrook I n s t i t u t e of Science, Cranbrook Press. Wright, B. S., 19i}-£>. Releasers of attack behaviour pattern i n shark and barracuda. Jour. Wild. Mang't., 12, 117-123. 

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