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Distribution, growth, feeding habits, abundance, thermal, and salinity relations of Neomysis mercedis… Wilson, Robert Riley 1951

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/ ? s v fa DISTRIBUTION, GROWTH, FEEDING HABITS, ABUNDANCE, THERMAL, AND SALINITY RELATIONS OF NEOMYSIS  MERCEDIS (HOLMES) FROM THE NICOMEKL AND SERPENTINE RIVERS, BRITISH COLUMBIA. by ROBERT RILEY WILSON A Thesis Submitted i n P a r t i a l Fulfilment of the Requirements f o r 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 A p r i l , 1951. ABSTRACT A study was made of the d i s t r i b u t i o n , feeding habits, growth, temperature tolerance and s a l i n i t y r e l a t i o n s of Neomysis mercedis. It was found to exist i n s a l t , brackish and fre s h water where i t feeds on diatoms, algae, vascular plant material, animal material and possibly detritus,. Growth to maturity appears to take one year with reproduction occurring i n the f a l l and possibly the springs There i s evidence of two populations, one produced i n the f a l l and the other i n the spring. Temperature tolerance was determined by subjecting animals from various acclimation temperatures to a range of temperatures and noting the times to death. The tolerance was determined, i n units of square degrees centrigrade, to be 491 units, with the lower and upper l e t h a l temperatures being 0°C. and 23°C An attempt was made to determine the rate of ac-climation to increasing temperature by r a i s i n g the temperature of separate groups of animals at d i f f e r e n t rates. Indications were that Neomysis acclimate thermally at a rate f a s t e r than 3°C. per day (1°C. per 8ohours). S a l i n i t y r e l a t i o n s were tested by subjecting animals from a constant s a l i n i t y to various lower s a l i n i t i e s ; by gradually reducing the s a l i n i t y of the environment; by subjecting animals from various s a l i n i t i e s to f r e s h water; and by setting up a s a l i n i t y or fre s h water preference gradient. About 1 o/oo c h l o r i n i t y was found to be l e t h a l f or Neomysis maintained i n an environment of 10.33 o/oo ch l o r i n i t y . Gradually decreasing the s a l i n i t y over a 6-day period i n d i -cated no increased a b i l i t y by the animals to withstand lower s a l i n i t i e s . There i s a temporal order i n the times to death of animals from various locations up the r i v e r ( i . e . animals from d i f f e r e n t s a l i n i t i e s ) when placed i n f r e s h water with those from regions of highest s a l i n i t y dying f i r s t . In some of the lower reaches of the r i v e r surface c h l o r i n i t y was ne g l i g i b l e yet Neomysis taken from these regions existed only for a limited time i n fre s h water. Those from upper reaches (10—14 miles upstream) survived well i n fresh water. The crustaceans exhibited no a b i l i t y to di s t i n g u i s h f r e s h from s a l t water. They did however exhibit a rheotaxic tendency. It i s suggested that the rheotaxic response, plus the animal's a b i l i t y to osmoregulate account for their d i s -t r i b u t i o n into f r e s h water. Indications are that Neomysis mercedis may be s u i t -able f o r transplantation into some lakes as a supplement to the f i s h food there. TABLE OF CONTENTS Page INTRODUCTION i DESCRIPTION 1 GENERAL DISTRIBUTION 3 DISTRIBUTION AND ABUNDANCE OF H. MERCEDIS IN THE NICOMEKL AND SERPENTINE RIVERS 5 MAP 11 GROWTH , 12 Method of analysis, 12 < Results 15 FEEDING HABITS 20 TEMPERATURE RELAT IONS 22 INTRODUCTORY REMARKS 22 EFFECT OF ABRUPT TEMPERATURE CHANGE 23 Method 23 Results 24 EFFECT OF GRADUAL TEMPERATURE CHANGE 33 Method.... 33 Results 33 EFFECT OF SIZE ON THERMAL TOLERANCE 34 Results 35 SALINITY RELATIONS 37 INTRODUCTORY REMARKS 37 HISTOLOGICAL EXAMINATION 39 Method..... 39 Results 40 EFFECT OF ABRUPT SALINITY CHANGE 43 Method 43 Results 43 EFFECT OF GRADUAL SALINITY CHANGE 45 Method 45 Results 45 EFFECT OF CHANGE FROM VARIOUS SALINITIES INTO FRESH WATER 47 Method 47 Results 47 SALINITY PREFERENCE. 47 Apparatus • <48 J Method 49 Results 50 DISCUSSION 53 SUMMARY 64 ACKNOWLEDGEMENTS LITERATURE CITED i INTRODUCTION The F i s h e r i e s Research Branch of the B r i t i s h Columbia Game Department was interested i n obtaining a type of plankton organism which would be suitable f o r introduction into lakes as a supplement to the e x i s t i n g trout food. P a r t i c u l a r l y were they interested i n oligotrophic lakes such as Kootenay lake where the Kamloops trout (S. g a l r d n e r i i ) grow quickly to about 8 inches i n length then slow i n growth t i l l reaching 16 inches (two pounds approximately) aft e r which they are large enough to feed on kokanee and consequent-l y speed t h e i r growth u n t i l they reach f i f t e e n to twenty pounds. The slow growth period was thought to be caused by a lack of suitable plankters. Mysis r e l i c t a and Pontoporeia a f f i n i s were suggested as supplements f o r lakes with sparse bottom fuana (Larkin, 1948) and consequently several thousand of these animals from Waterton lakes, A l t a . were transplanted into Kootenay lake, B. C. Subsequently some preliminary experimental work was carried out on these crustaceans i n the laboratory but i t was found impractical to maintain a s u f f i c i e n t l y large stock. In September, 1950, a Mvsldacean (Neomysis mercedis) was found i n the brackish water estuary of the Nicomekl r i v e r . Since i t had also been reported i n Lakelse lake i t might be suitable f o r introduction i n t o f r e s h water. Accordingly c o l l e c t i o n s were made with a view to determining some of the sali e n t c h a r a c t e r i s t i c s of these crustaceans i n r e l a t i o n to the i r possible transplantation. If introductions are to be made, insight into feed-ing habits, growth rate, times of reproduction, abundance, thermal tolerance and s a l i n i t y tolerance might be of primary importance. The following, therefore, i s an endeavor to throw some l i g h t on these f a c t o r s . 1. DESCRIPTION Specimens have been identified (A, H. Banner, 195D as Neomysis iriercedis Holmes of the family Mysidae. order Mysidacea. sub class Malacostraca. class Crustacea. The organism has been adequately described by Tattersal (1932). For the present study a short review of the development and a description of i t s secondary sex charac-t e r i s t i c s are sufficient. The animal has no free livi n g larval stagesj eggs and young develop i n a brood pouch formed by plates (oostegites) on the last two thoracic segments of the adult female. Young are liberated when 3—4 mm, long and are then replicas of the adult. Mature adults are 9—10 mm, in length (from eye to base of telson), but growth may proceed to 13 mm, in some individuals. In females the brood pouch i s characteristic of the adult. The genital pores are on the sixth thoracic segment at the base of the appendages. The pleopods are a l l uniform in size. In males the genital pores are on the last thoracic segment. The fourth pleopods of the adult are biramous and have extended exopods, presumably for sperm transfer. It might be noted here that in the February and March collections the animals were infested with Zoothamnion arbuscula, a member of the family V o r t i c e l l i d a e . The proto zoan i s not p a r a s i t i c and i s believed to be harmless to the crustaceans. 3 GENERAL DISTRIBUTION N. mercedis was f i r s t reported from lake Merced, a f r e s h water lake on the San Francisco peninsula, C a l i f o r n i a , ( T a t t e r s a l , 1932). Since then i t has been collected i n San Francisco bay ( T a t t e r s a l , 1932)} Nanaimo and Departure bay, and Quatsino sound, Vancouver i s l a n d ; Lost Lagoon, Vancouver, (Ta t t e r s a l , 1933)• 1* &as also been found i n Lakelse lake and was i d e n t i f i e d from there by A. H. Banner (Cha'ce^ June 3,1949). Dr. S. C. C a r l ( l e t t e r to author) t e n t a t i v e l y i d e n t i f i e d a mutilated specimen from St. Mary's lake, Salt Spring i s l a n d , as Mysis r e l i c t a and mentions a record of Mysis from lake Washington near Seattle. Since then Banner (1951) has reported that Neomysis  mercedis occurs i n lake Washington. I t might be, as Dr. C a r l did suggest, that t h i s i s a c t u a l l y the species i n St. Mary's lake. The animals used i n the present work were discovered i n the estuaries of the Nicomekl and Serpentine r i v e r s . So f a r as can be ascertained there i s no previous record of them from t h i s l o c a l i t y . Neomysis mercedis i s predominantly a brackish water species, although i t has been taken i n regions of r e l a t i v e l y high s a l i n i t y and also i n f r e s h water. In San Francisco bay i t i s limited l a r g e l y to the upper part of the bay; T a t t e r s a l (1932) believes the r e l a t i v e l y high s a l i n i t y of the lower bay to be most important i n e f f e c t i n g t h i s r e s t r i c t e d d i s t r i b u t i o n . In the Serpentine and Nicomekl r i v e r s the species occurs from the mouths of the f i v e r s to fourteen miles upstream where the water i s f r e s h . 5. DISTRIBUTION AND ABUNDANCE OF M. MERCEDIS  IN THE NICOMEKL AND SERPENTINE RIVERS. A b r i e f account of the physical c h a r a c t e r i s t i c s of the r i v e r s i s applicable to t h i s section of the work. Both r i v e r s drain low l y i n g land i n a v a l l e y running easterly from Mud bay ( f i g . 1). They are slow flow-ing, winding and f a i r l y muddy. Since about 3/5 of each r i v e r i s below the 25 foot contour l i n e a large portion i s affected by the t i d e s . The t i d a l influence causes large d a i l y variations i n the r i v e r l e v e l s but the amount of sea water i n the r i v e r s i s limited by f l o o d gates about 3 miles from the mouths. These gates are constructed so that they are open when the force of the r i v e r current i s greater than that of the incoming tide and closed when the t i d a l flow equals or exceeds that of the river. Thus at high tide the gates act as a dam causing the r i v e r s to back up. The ef f e c t of t h i s has been noted 9§ miles up-stream. Although most of the sea water i s kept out, some does flow up the r i v e r s past the flood gates. On January 27, surface and bottom water samples were taken a quarter of a mile above the flood gates on the Nicomekl. The surface sample gave a n e g l i g i b l e c h l o r i n i t y while the bottom sample showed a c h l o r i n i t y of 6 o/oo. Surface and bottom samples 6. both gave n e g l i g i b l e c h l o r i n i t i e s 8 miles upstream, i n d i c a t -ing the absence of an underlying layer of sea water th i s f a r up the r i v e r . Salient features of the abundance and d i s t r i b u t i o n of Neomysis are given i n Tables I and I I . These may be used i n conjunction with the map ( f i g . 1.) which indicates the exact l o c a t i o n of the c o l l e c t i o n s . In the tables the abundance l i s t e d as good, f a i r or poor, i s based on the number of individuals taken per sweep of the net. "Good" indicates 30 to 40 i n d i v i d u a l s , " f a i r " — 1 0 to 15, and'poor"—1 or 2. The animals were coll e c t e d by the use of a dip net which had a 9" diameter mouth, was made of cheese c l o t h and was attached to the end of a 6' wooden handle. Collections were made from the banks of the r i v e r s . Most Crustacea were found i n reedy or grassy locations where the bank sloped gradually into the r i v e r . Where the r i v e r bank was v e r t i c a l or overhanging, Neomysis were taken close against the bank, or under the overhang, although i n such locations c o l l e c t i o n s were never large. At the r i v e r mouths where the shore of Mud bay slopes very gradually, Neomysis were collected i n about 18" of water 10* off shore when the tide was low (about 6'). The bottom here i s a mixture of mud, sand and gravel. Reeds and grasses grow farther back on the shore and are under water at high t i d e . 7. As shown i n f i g . 1, Neomysis were taken from the mouth upstream lOf miles i n the Serpentine, and 14 miles i n the Nicomekl. The l a t t e r r i v e r i s more l i k e a creek i n t h i s location, being small and f a i r l y f a s t flowing. The g r e a t e s t abundance of Crustacea occurred i n the f a l l c o l l e c t i o n s of October and November (Table I). At t h i s time the animals taken were n e a r l y , a l l females of which many were carrying eggs or young. Compared with these catches the numbers of animals i n succeeding c o l l e c t i o n s was very much reduced. TABLE I — COLLECTIONS IN NICOMEKL DATE TIME LOCATION — Mi.From Mouth ABUNDANCE & REMARKS TIDE (Approx. Height) SURFACE CHLORINITY . 0 / 0 0 SURFACE TEMP. °C, Oct.9/50 1200 4£ Very Good-Nearly a l l females many with brood pou-ches. 9" 3 . 1 12 .0 Oct.22/50 1400 4*. Good-Nearly a l l females.. Many brood pouches. 1 2 i 9 . 5 Nov.5/50 1200— 1400 1130 3 Drainage d i t c h along H'wy. Good-Nearly a l l female. None. 13* N e g l i g i b l e 9 . 0 11 .0 Dec.12/50 1330 1400 1600 3 4 4 None. Very poor. F a i r — M a l e s and females taken. 12 • 12' 12' . 5 4 N e g l i g i b l e 7 . 0 7 . 0 6 . 5 Dec.17/50 1430 1500 3 9 t None by scoop net. Few by bottom drag net. F a i r 13 • 12' . 5 0 N e g l i g i b l e 6 . 5 5 .9 Dee.19/50 2100 2130 2200 3 2 9 i 1 only seen None None 4« 5« 0 . 4 N e g l i g i b l e 6 . 0 5.8 Jan.12/51 1000 1200 k None F a i r . Very few males. 15* 1 2 ' . 0 7 . 0 7 • 6 . 0 1 TABLE I — CONTINUED. DATE TIME ., LOCATION Ml.Frofii Mouth ABUNDANCE & REMARKS TIDE (Approx. Height) SURFACE CHLORINITY 0/00 SURFACE TEMP. °C. Jan.21/51 1300 1500 1600 2 I i Poor. F a i r . Very few males None. 5 taken. 12' 13' 12« .523 : .523 N e g l i g i b l e N e g l i g i b l e 6.5 6.5 6.5 6.2 Jan.27/51 1430 1600 1630 Mouth k None. None. 1 only. 8» 9' 10 • R 3.66 N e g l i g i b l e N e g l i g i b l e 5.0 4.5 4.5 Feb.3/51 1400 150G 1600 2 3 Poor. None. Very Poor. None. 14' 13' 12» N e g l i g i b l e N e g l i g i b l e .4 N e g l i g i b l e 3.0 3.0 3.0 3.0 Feb.. 17/51 1600 1645 Mouth (Actually Mud B # F a i r -Poor. 8' V 7,. 4-2 N e g l i g i b l e 5.0 4.0 Feb.24/51 1400 1430 1500 14 ( L . P r a i r i e ) River small here. 4 Poor. None. Poor. V 7» 8« N e g l i g i b l e N e g l i g i b l e N e g l i g i b l e 4.0 4.0 4.0 Mar.17/51 1430 1500 1430 1530 1630 Mouth-Mud bay Short D i s t . up r i v e r . H F a i r . F a i r . Poor. Poor. j F a i r . _ g l • 8' 8' 8» 7» 3*63 1.34 N e g l i g i b l e N e g l i g i b l e Negligible 6.0 5.0 4.0 4.0 4.0 TABLE II — COLLECTIONS IN SERPENTINE DATE TIME LOCATION Mi.from Mouth ABUNDANCE & REMARKS TIDE (Approx. Height) SURFACE CHLORINITY 0/00 SURFACE TEMP.°C. Dec.12/50 1500 None 12» Negligible 6.5 Dec.17/50 1400 2£ None 12' .7 5.0 Dec.19/50 | 2145 n None 4J Negligible 6.0 Jan.12/51 | 1300 None 11' .20 6.0 Jan.21/51 1430 Mouth Good 13' 7.57 5.0 Jan.27/51 1600 6J None , 9« Negligible 4.5 Feb.3/51 J 1500 Mouth Good 131 10.33 3.0 Feb.24/51 1330 F a i r . River had been high. 71 Negligible 4.0 Feb.24/51 1445 None 8» Negligible 4.0 f i g . 1. Locations of c o l l e c t i o n s of Neomysis i n Nicomekl and Serpentine r i v e r s . ft 3 MAP SHOWING COLLECTIONS  OF N EOMYSIS IN NJCOMEKL AND SERPENTINE RIVERS ~ NO NFOMYS/S TAKEN  *<** ~ NEOMXS/S TAKEN -SEE TABLES I&H F~OIP r>F~ TA// c _ / 4 M i l NlCOMCKL Scale. 1=1 mile. 12. GROWTH Method of Analysis The growth analysis i s based on measurements f o r females col l e c t e d during the months of October, November, February and March. The c o l l e c t i o n s i n these months were made i n the same general l o c a t i o n i n the r i v e r whereas c o l l e c t i o n s i n December and January were made i n d i f f e r e n t areas. It was considered that the animals obtained up the r i v e r where the s a l i n i t y i s low might possibly grow at a d i f f e r e n t rate from those nearer the mouth, consequently the r e s u l t s of the December and January samplings were omitted from the c a l c u l a -tions. Only females were numerous enough f o r consideration i n the October and November c o l l e c t i o n s . Crustaceans, having exoskeletons, grow only during the moulting period. Growth may be followed by determining the i n t e r v a l s between moults from the modes i n length frequency polygons. Some d i f f i c u l t y was experienced i n determining the modal peak f o r size classes by inspection. Therefore a method described by Harding (194-9) has been used to e s t a b l i s h the modal peaks. His method consists of p l o t t i n g accumulated per-centages on p r o b a b i l i t y paper. In a normal d i s t r i b u t i o n , i f the variates be taken as percentages of the t o t a l number of variates and these percentages then be accumulated and plotted on p r o b a b i l i t y paper the r e s u l t i n g graph i s a straight l i n e . Thus i f , from a sample, two straight l i n e s appear when using 13. t h i s method the inference i s that the sample i s comprised of two populations. The calculations (Table I I I ) , and graph ( f i g . 2.), f o r the c o l l e c t i o n s of February—March follow as an example of the use of the method. TABLE I I I — DATA FROM FEBRUARY.--MARCH COLLECTIONS USED TO PLOT GRAPH IN FIG. 2. Size mm. Eyes-Base Telson Frequency % Frequency % Accumulated 6 9 6.72 6.72 7 16 11.94 18.66 8 17 12.69 31.35 9 15 11.20 42.55 10 23 17.16 59.71 11 33 24.61 84.32 12 15 11.20 95.52 13 5 3.73 99.25 14 1 0.75 100.00 134 100.00 The plots of the accumu£at'edi percentages (dotted l i n e i n f i g . 2. r e s u l t i n two straight l i n e s representing two populations or age classes, the l i m i t s of which are indicated by the point of i n f l e c t i o n i n the curve jo i n i n g the straight l i n e s . The smaller size class i s taken to be 39$ (point of i n f l e c t i o n ) and the larger size class i s taken to be 61$ of the whole sample. Each of these classes i s treated inde-pendently and plotted on the p r o b a b i l i t y paper as though i t 0.61 0.1 Q 2 0 l 5 i "2 5 15 20 3'0 4'0 50 60 70 80 96 95 9'8 99 9 9 . 9 99.99 ACCUMULATED PERCENT FREQUENCY f i g . 2. Length of Neomysis plotted against accumulated M percentage frequency. 15. occupied the whole range of 100$. Using the class of smaller indivi d u a l s (occupying 39$ of the sample) as an example, t h i s i s done by multiplying the accumulated percentages of the group by These values produce a straight l i n e when plotted (lower s o l i d l i n e i n f i g . 2.). The point where i t cuts the 50$ v e r t i c a l i s taken to be the mean size of the class read off on the ordinate. The standard deviation of th i s mean i s determined by projecting v e r t i c a l s 34.13$ each side of the 50$ v e r t i c a l . These v e r t i c a l s intersect the l i n e representing the age c l a s s . The values of the points of int e r s e c t i o n read off on the ordinate give the standard devi-ation each side of the mean. E s s e n t i a l l y the same procedure i s adopted f o r the other age class so that the mean and standard deviation f o r each can be determined. Results Since the October and November c o l l e c t i o n s were but two weeks apart and the February—March c o l l e c t i o n s three weeks apart, the data of the spring samples were combined and so were those of the f a l l samples. Table IV l i s t s the frequency of appearance of the various size classes f o r the combined c o l l e c t i o n s . These data are graphed i n f i g . 3. Treating i t by Harding's method gives averages f o r si z e classes as f o l l o w s : — October—November collections—5.8mm.(S.D.-1.0) and + 9.3 mm. (S.D.-1.2) February—March c o l l e c t i o n s —7.1mm.(S.D.-1.0) and 10.4 mm. (S.D.±1.2) 16. TABLE IV — COMBINED COLLECTIONS OF OCTOBER—NOVEMBER AND FEBRUARY—MARCH. Size mm. Eyes-Base Telson Frequency (No. Individuals Collected) October— November February— March 1 4 1 5 4 • 6 15 9 7 10 16 8 21 17 9 32 15 10 39 23 11 23 33 12 10 15 13 2 5 14 1 157 134 It would seem that there were two periods of r e -production each year. One period i s known to occur i n September and October (observations i n the f i e l d ) . This would produce the 5.8 mm. class of the October—November sample, with 7.2 mm. representing the size of t h i s class i n the spring. Growth would l i k e l y bring t h i s class to about 10 or 11 mm. by August with reproduction occurring i n the f a l l . I t i s suggested that after releasing the young the majority of females perish, while a few survive to reach a 17. o <*1 o w as o-CM A Vs. T o St o 53 o> o ttf CM 04 ^ IF" ' LENGTH MM, 12 o \ 0 ~b" : 10~ LENGTH MM. I T $ i g . 3» Lengths-frequency polygons for Neomysis mercedis; * Upper diagram October—November col l e c t i o n s . Lower diagram February—March c o l l e c t i o n s . 18. size of 12-13 mm. i n the spring when they again reproduce. The presence of the 9.3 mm. group i n the October— November c o l l e c t i o n s can be accounted f o r by supposing a reproductive period i n the spring possibly around May—June. The f a c t that egg bearing females (12—13 mm.) were taken i n the February—Harch c o l l e c t i o n s lends some support to t h i s suggestion. The pattern of growth i s indicated diagrammatically i n f i g . 4. The cross hatched areas represent the suggested growth of the animals throughout the year. YOUNG RELEASED fig . ' 4 . Diagrammatic representation o f suggested growth of N„ mereedis. These conclusions may be presumptuous considering the supporting data. Some reproduction may occur during the whole year. However, f i e l d observations indicate a heavy breeding period i n the f a l l , and c o l l e c t i o n s (small as they are) indicate a period i n the spring as w e l l . It remains f o r 1 2 monthly c o l l e c t i o n s to be taken before d e f i n i t e con-clusions can be reached. 20. FEEDING HABITS Borradaile (1935) describes the feeding mechanism of Mysidaceans. Food p a r t i c l e s are carried to the mouth i n a current of water set up by rapid movements of the maxillae. Large pieces of material are held by the endopodites of the thoracic limbs while being eaten. In order to determine the type of food eaten the stomachs of 33 f r e s h l y caught animals were examined. In most cases much of the material was u n i d e n t i f i a b l e , suggesting d e t r i t u s j however, i t was found that both plant and animal organisms were consumed. Diatoms, d i n o f l a g e l l a t e s , blue green algae, vascular plant and animal material were observed. Copepod and mysidacean remains seemed to comprise the greatest part of the animal matter. Diatoms and animal remains were part of a l l contents examined. Very often the diatoms had been well digested so that only the she l l s were l e f t . Recog-nizable vascular plant material occurred i n 85$, d i n o f l a g e l -lates i n 35$, and blue green algae i n 35$ of the stomachs. The figures f o r d i n o f l a g e l l a t e s and blue green algae may be considered as approximate. While some of the diatoms i n the stomach contents were decomposed suggesting they had been taken up by other-, Crustacea which had f a l l e n prey to the Neomysis. others were i n remarkably good condition. It appears that N. mercedis 21. feeds on such plankters as well as on larger organisms. The animals i n c a p t i v i t y are c a n n a b i l i s t i c but incapacitated i n d i v i d u a l s are most often attacked. They were also observed to feed on dead sticklebacks i n one of the aquaria. In the laboratory they obtained food from detritus material on the bottom of the aquaria. A supplemental food was supplied consisting of a ground-up mixture of dried plankton, dried daphnia eggs, and dried canned salmon. Micro-examination of the stomach contents of animals held i n d e t r i t u s free water f o r 21 days showed that t h i s mixture of food was eaten. 22 TEMPERATURE RELATIONS  INTRODUCTORY REMARKS The e f f e c t s of temperature on animal and plant organisms were studied early i n the annals of physiology. This was perhaps due to the f a c t that temperature experiments were r e l a t i v e l y simple to carry out. Davenport (1908) has tabled the re s u l t s of temperature experiments performed on some 85 types of tissue and animals by early workers. The st r i k i n g thing about t h i s table i s the f a c t that time and again the upper l e t h a l temperature of an organism i s ci t e d with no mention of the method used to determine t h i s temp-erature. Jacobs (1918) states that the e a r l i e r workers were interested c h i e f l y i n the so-called upper thermal death point, and that they overlooked the time factor i n the i r work. The a b i l i t y of animals to acclimatize themselves to temperature changes eauses a d i f f i c u l t y i n the determination of t h e i r thermal tolerance which was overlooked by these workers. It i s now generally r e a l i z e d that the thermal history of most organisms i s of the utmost importance with regard to the i r tolerance to heat and/or cold. This f a c t i s exemplified by Davenport's experiment with Bufo tadpoles (Davenport, 1908X Those tadpoles maintained at 15°C went into heat r i g o r at 40.3°C. If kept at 25°C f o r 28 days heat r i g o r was not produced u n t i l the temperature had been raised to 43 . 5 ° c » Loeb and Wastenays (1912) found that Fundulus maintained at 23. 10°C. were k i l l e d i n a few minutes at 35°C., whereas Fundulus kept at 27°C.for 40 hours were able to endure 35°C. temper-atures i n d e f i n i t e l y . Results of experiments of thi s nature are given by Hathaway (1927) or Behr (1918). To overcome the eff e c t s of time and acclimation a method may be employed wherein the animals being tested are subjected suddenly to higher or lower temperatures and the time to death noted. The method used here i s of t h i s nature, being patterned after that used by Brett (1941) and Fry, Brett and Clawson (1942). EFFECT OF ABRUPT TEMPERATURE CHANGE  Method The Neomysis used i n the temperature experiments were taken from the Nicomekl and Serpentine r i v e r s . Individ-uals of both sexes and of a l l sizes were used. The crustaceans, on being brought to the laboratory, were placed i n constant temperature (±0^5°C.) aquaria. In these aquaria they obtained food from a small amount of r i v e r bottom sediment, by feeding on dead and dying Neomysis or from a mixture of daphnia eggs ground up with dried canned salmon. From the water at constant temperature (acclimation temperature) groups of shrimps were transferred to 3000 ml. beakers containing 1000 ml. water. The water was maintained at various test temperatures by placing the beakers i n constant 24. temperature aquaria. Thermoregulators maintained the water temperatures constant within t 0.5° c» The water i n the beakers and i n the aquaria was agitated by using air-breakers connected to the compressed a i r l i n e . This served to keep the temperature throughout the aquaria and beakers uniform. For temperatures below that of running tap water three r e f r i g -eration units were ava i l a b l e . M o r t a l i t i e s were checked, when possible, every 2 hours during the f i r s t two days of the experiments. Where several m o r t a l i t i e s occurred overnight the times to death were interpolated, consideration being taken of the condition of the animals at the l a s t observation. Results Tables V, VI, and VII present the r e s u l t s f o r the temperature experiments. In the l e f t hand column are l i s t e d the test temperatures to which the organisms were subjected. The v e r t i c a l l i n e s to the right of t h i s column, numbered 0 to 100 from l e f t to r i g h t indicate percent of the individuals dying at the various test temperatures; (reading from right to l e f t indicates percent s u r v i v a l ) . The numbers i n the columns represent the hours elapsed from the start of the experiment to the time of death of that percentage of in d i v i d u a l s as indicated by the column. For example, i n Table V at a test temperature of 1.8°C. the number 21 i s seen i n the f i r s t column with a small v e r t i c a l red mark about 2/3 of the way across the column. This indicates that f o r Neomysis acclimated to 6°C., about 6$ (indicated by small v e r t i c a l red mark) of those subjected to a test temperature of 1.8°C. died or 94$ 25. were surviving i n 21 hours. This type of table records the whole picture r e-garding times to death i n various temperatures. It w i l l be noted that i n the tables the percent of animals dead or sur-viving was not always recorded at 48 hours, t h i s occurred because i t was not always possible to take readings at these times. In such cases the percent s u r v i v a l was interpolated. Figure 5 represents these data graphically f o r the s u r v i v a l at 48 hours. Figure 6 was drawn from the same data as f i g . 5. Fry, Brett and Clawson (1942) used t h i s method i n describing the thermal tolerance of gold f i s h . For trout Brett concluded that i f the f i s h could stand a c e r t a i n temperature f o r 14 hours they could tole r a t e i t " i n d e f i n i t e l y " . Temperatures which he ca l l e d l e t h a l were those which k i l l e d 50$ of the f i s h during a period of 14 hours. This same general procedure was adopted f o r Neomysis although i t was found that there was no time beyond whieh the crustaceans would l i v e " i n d e f i n i t e l y " . I t was d i f f i c u l t to maintain the animals i n the laboratory and even i n the controls there was considerable mortality. (Tables V, VI and VII) In the Neomysis experiments, 48 hours was a r b i t r a r i l y chosen as the time period upon which to base the l e t h a l temp-erature determinations. Thus the temperature at which 50$ of the Neomysis died at 48 hours after being acclimated to a given temperature i s taken to be the " l e t h a l temperature" f o r TABLE V — TIMES OF SURVIVAL OF NEOMYSIS FROM 6°C ACCLIMATION IN VARIOUS TEST TEMPERATURES. (DESCRIPTION E L TEXT.) . . . Test Temp. . ° c : < IOC 1( 9< ) 2 ) 8 3 ? 0 4 0 6 & DEAD y . -5 J ALIVJ 3 ... 6 3 4 3 7 > 3 3 8 3 2 3 9 3 1 3 1( 3 < •0 1.8 21 1 48' 64' ' 87 ' 192 ' 27 48 1 65 ' 1 83 1 8 5 ' 3.0 50 ' 61 ' '95 10.0 4-9 1 59 ' 70' 13.0 4 0 ! 65' 94 1 19.8 1 1 3' 4<!> ' 73 'l92 1 3 22 ' 46* '73 192 21.0 21 1 251 ' 1 45 51 7 J ' 2 192 23.0 21 1 2 5 ' *33 '45 ' 51 1 72 192 ' Controls 45 1 ' 72 100 ' L26 ' f 142 192 / 71 100 I 142 1 192 -• TABLE VI — TIMES OF SURVIVAL OF NEOMYSIS FROM 14°C. ACCLIMATION IN VARIOUS TEST TEMPERATURES. (DESCRIPTION IN TEXT.) Test Temp. ( °C. 1< ) 1 )0 9 3 2 3 c 0 3 0 7 0 A 0 i % DEAD o _5 $ ALIVE o 5 3 6 3 4 3 7 3 3 3 8 3 2 0 9 D 1 0 1 0 30 3 2 s 1 '21 1 30 i 2-1 [ '3. 1 '7J 1 5 51 | 70 ' 105 3.6 45 1 70 ' 1Q.5 18 54' '101 119 ' 61 1 93 ' 22 47 23 4 1 1 31 53 ' 70 9. >' 1171 2 I '20 1 47 J 73' 93 'H! 24 1 ' l 22 LL 5 8 70 l 22* '25 J3 46' 70 ' 6 ' r l 7 '21 '44 '64 fe7 124 ' '5 ' 14* '26 '48 fco j87 '12' 25 20 30 40 1 68' '3 . '16 :'i7 N- !24 _ 20 1 30' 1 ' 40 50 ' 68 26 1 k 1 4 | 1 271 43' 1 16 ' 18 ' ' 20 '24 1 1 1 1 40 TABLE VI — CONTINUED Test Temp. ( OC. 1 ( >o < .0 2 0 i G 3 0 7 0 4 0 6 % DEAD ^ 5 $ ALIVE 0 5 1 0 t 0 A 0 7 0 3 3 8 3 2 3 S 3 1 0 1< 0 < )C ) 27 i ' 2 2 * ' 1 4 44 7 16 Controls 54- 1 74 ' 9 5 / 124 --do '81 ' 103 - • — • 1 61 I 7 6 ' 120 1 131 1 4 1 3EX a l l were extremely inactive x temperature went up to 26°G. f o r several hours. These r e s u l t s Ignored when pl o t t i n g graph. ro 00 TABLE VII ~ TIMES OF SURVIVAL OF NEOMYSIS FROM 2 0 O C . ACCLIMATION IN VARIOUS TEST TEMPERATURES• (DESCRIPTION IN TEXT.) Test Temp, i 1.8 ) 1 )0 s 0 2 0 £ 0 3 0 7 3 1 3 i $ DEAD 0 .5 $ ALIVE 0 5 0 6 0 4 0 7 — 0 £ 0 2 • _______ 0 s 0 3 0 1( 0 ( )C ) ~r 3 . 0 10'j 24 1 4 8 1 7 1 ' 4.7 I 24 1 4 8 1 57 1 * J 9 3 1 1 7 ' 1 6 5 1 n _ i j '24 48» 51 7 1 s 8 0 ( 1 1 2 7.6 53 J 71 1 112 1 14 . 0 531 I 7 4 87 1 21.3 \ 27 M 4 5 t 1  j 1 1 '71 , 24 . 0 j'6 2 1 » 4 7 1 5 1 1 701 144 I 24.8 1 0 h 2 4 T » " l 2 48 1 6 0 Ii 24.8 7' J '9 '24 »3l '48 »6C 1 2 0 * 25.6 H 1 ' 2 1 4 8 1 25.6 l ' 2 1 ' 2 9 1 4 8 ' 5 7 ' 27 .2 '4 181 Controls 63' 791 HO 1 1 2 9 1 1 6 5 1 6 0 ' 701 181 114l 140 1 -ro vo 7£ r— 10 12 14 TEST TEMPERATURES —Q. 6°C. ACCL. * -14°C. ACCL, ACCL. 16 W DEG, CENT, 28 f i g . 5. Percent s u r v i v a l i n various temperatures of Neomysis acclimated to 6 o c., 14-OC., and _ 0 o C . i__2_y_t__ 31 . f i g . 6 . Thermal tolerance of Neomysis. (Description i n t e x t T T < 32. these animals at t h i s p a r t i c u l a r acclimation temperature. The period of 48 hours was considered ample since these animals c h a r a c t e r i s t i c a l l y exhibit d i u rnal migrations and even though they inhabited the upper warmer strata of lakes or r i v e r s p e r i o d i c a l l y , the length of time spent there would be but a f r a c t i o n of 48 hours. In f i g . 6. l e t h a l temperatures are plotted against the acclimation temperatures. According to Fry (1947) the diagonal l i n e represents the point where both the l e t h a l and acclimation temperatures are the same. The place where the upper l e t h a l temperature l i n e crosses t h i s diagonal indicates the l i m i t of acclimation to the higher temperatures. Since acclimation can proceed no further i n t h i s d i r e c t i o n a perpendicular may be dropped from t h i s point to the lower l e t h a l temperature l i n e . Had the lower l e t h a l l i n e run into the diagonal then a perpendicular could be raised from the int e r s e c t i o n to the upper l e t h a l l i n e . However, water becomes ice at a temperature above the t h e o r e t i c a l ultimate lower l e t h a l l e v e l so that the actual lower l e v e l i s at G°C. or just s l i g h t l y above. The resultant area, enclosed by the axes, the upper and lower l e t h a l l i n e s , and the perpendicular on the r i g h t , indicates the range of temperatures that Neomysis can t o l e r a t e . The area may be measured i n Centigrade units of one square degree. Thus the thermal tolerance of these crustaceans can be stated as being 491 Centigrade units ( or square degrees C ) , with the upper l e t h a l temperature l i m i t 23.6°C. and the lower l e t h a l temperature l i m i t of 0°C. Fry, Hart and 33. Walker (194-6) found a value of 625 units f o r yearling speckled trout, Salvellnus f o n t i n a l i s . and Brett (1944) found 1160 units to be the thermal tolerance of the bullhead, Ameirus  nebulosus. It i s r e a l i z e d that the thermal tolerance of Neomysis may vary with sex but i t i s considered that such deviations would not be of s u f f i c i e n t magnitude to affe c t the value of t h i s f i g u r e . EFFECT OF GRADUAL TEMPERATURE CHANGE  Method F i f t e e n to twenty Neomysis were placed i n 1000 cc. water i n 3000 cc. beakers which were kept i n water baths. The low temperatures were maintained by r e f r i g e r a t o r units and the upper temperatures by immersion coils—thermoregulated to *0.5°C. Three tests were carried out. In one the temp-erature was raised 1.0°C. per day, i n another 1.5°C per day, and i n the t h i r d 3.0°C. per day. Figure 7 i l l u s t r a t e s the re s u l t s i n presenting the time and temperature f o r 50$ s u r v i v a l at the various rates of temperature increase. Results The:.graph indicates that indi v i d u a l s subjected to a r i s i n g temperature of 3°C. per day survived a higher temper-ature than those subjected to 1°C. per day increase. This would suggest that the rate of acclimation was greater than 3°C. per day f o r indivi d u a l s maintained at approximately 7.5°C. If acclimation had proceeded at a rate slower than 34. t h i s then animals with environmental temperatures r i s i n g at 1°C. or 1.5°C. per day should have survived higher temper-atures than those whose temperature was raised more quickly. <f\T •*vO :>'H" H i Si as. D .rvCM -i'.CO-or > so, > CO o O t-i I in X I I CM cxr 6H I 1 1 r -RATE OF TEMP. INCREASE (C.0/DA_1. I f i g . 7. Time and temperature f o r 50$ sur v i v a l of Neomysis undergoing various rates of temperature increase. EFFECT OF SIZE ON THERMAL TOLERANCE In order to determine whether age affected the sur v i v a l a b i l i t y i n various temperatures, note was taken during several of the tests of the size of the animals and the order i n which they perished. The data col l e c t e d are 35. represented i n Table VIII. From these data the average sizes of the f i r s t $0% and the l a s t $0% dying were determined.and the standard error of the difference of the means of these tv/o was calculated. Results The r e s u l t s indicate that there i s a s i g n i f i c a n t difference dat the .05 p r o b a b i l i t y level) between the sizes of Neomysis dying f i r s t and l a s t i n high temperatures. The indications are that smaller animals are more r e s i s t a n t j however, significance i s not shown at the .01 p r o b a b i l i t y l e v e l which indicates the necessity of a r e p e t i t i o n of t h i s experiment. 36 . TABLE VIII — DATA AND CALCULATIONS FOR DETERMINING EFFECT OF AGE OF NEOMYSIS ON UPPER THERMAL TOLERANCE. TEMP. °C. SIZE (MM.) IN ORDER OF DEATH LCCL. TEST 1s t DYING LAST DYING AVERAGE AVERAGE 6 21.8 9 . 0 , 1 1 . 0 , 9 . 0 10 .0 9 .75 1 1 . 0 , 9 . 0 , 8 . 0 , 6 . 0 8.50 14 23 9 . 0 , 9 . 0 , 1 0 . 0 9.33 8 . 0 , 6 . 0 , 8 . 0 7.33 23 6 . 0 , 1 0 . 0 8 .00 9 . 0 , 1 1 . 0 10.00 24 1 1 . 5 , 1 1 . 0 , 9 . 5 , 1 0 . 0 10.50 6 . 0 , 9 . 5 , 9 . 5 , 7 . 0 8.00 24 1 0 . 0 , 1 1 . 5 10 .75 1 0 . 0 , 9 . 5 9 .75 24 1 0 . 0 , 7 . 0 , 1 0 . 0 , 1 0 . 0 9 .25 9 . 0 , 9 . 0 , 1 0 . 0 , 6 .0 8 .50 25 1 2 . 0 , 9 . 0 , 1 1 . 0 1 0 . 0 , 11 .0 10.60 8 . 0 , 1 0 . 5 , 9 . 0 , 1 0 . 0 , 10 .0 9.50 25 8 . 0 , 9 . 0 , 1 1 . 0 , 8 .0 9 .0 7 . 5 , 8 . 0 , 1 0 . 0 , 10 .0 8.88 20 24.8 io.5, l i . o 10 .75 8 . 0 , 6 . 5 7 .25 Av. Total x = 87.93 9 .77 y = 77.71 8.63 S.D.x " .9023 S.D.y .8676 Dm. 3 1.14 S.E.x .3007 s.E.y = .2892 S.E.D. e .417 t a 2 .733 3 7 . SALINITY RELATIONS INTRODUCTORY REMARKS In order to e x i s t , aquatic animals must maintain t h e i r body f l u i d s at the same concentration as the external environment or else u t i l i z e some means of osmoregulation. Many forms have very li m i t e d powers of osmotic control. Others, those which move from s a l t to f r e s h or brackish waters, have well developed means f o r maintaining body s a l t balance i n changing environments. For example the cr a y f i s h , which can tolerate a range of s a l i n i t i e s , does so by producing large volumes of hypotonic urine, and by active s a l t absorption through the g i l l s . The marine crab, Eriocheir« which can exist i n f r e s h water produces isotonic or hypertonic urine but has a very low s a l t and water permeability. It can also absorb chloride ions through the g i l l s (Prosser, 1 9 5 0 ) . Between these two methods there i s a range of s p e c i a l i z a t i o n from high to low impermeability, from isoto n i c to hypotonic urine production, and from small to large powers of sa l t and/or ion absorbtion or retention. In conjunction with these diverse methods, various animals employ d i f f e r e n t organs f o r osmoregulation. Marshall and Smith (1930) have shown that the kidney of f r e s h water teleosts i s important i n osmoregulation. The anal g i l l s of the larvae of the mosquito-, Aedes aegypti ? are claimed by Wigglesworth (1933) to function as osmoregulators by absorbing 38. water. Schlieper and Herrmann (1930) and Schlieper (1930) believe that the body surface of the crabs, Potamon fluviatele and Eriocheir sinensis T is an organ of osmoregulation. These workers have also produced evidence of the importance of the excretory organs in this function. Lienemann (1938) credits the green glands (antennal glands) of Cambarus c l a r k i l with playing a part in osmotic regulation. This same organ is claimed by Samuel (194-5) to be the most important structure for osmoregulation in the decapods. This conclusion i s opposed by Pannikkar (194-1) who claims that in the prawns, at least, the g i l l s bear most of the burden for maintaining osmotic balance. Although the present study i s more concerned with salinity tolerance of Neomysis than with the physiology of the osmoregulatory function some familiarity with the organs supposedly concerned may be desirable. In general the organs claimed to be active in osmoregulation are g i l l s , excretory organs and skin (external covering). As far as can be determined Neomysis lack g i l l s , which leaves but the skin (chitinous exoskeleton) and the excretory organ (antennal gland) to be considered. This latter structure could not be seen by dissection methods so long-itudinal and transverse serial sections were made which were sufficient to provide a brief description of the histology of the organ. 39.. HISTOLOGICAL EXAMINATION  Method Because the animals possess a chitinous exoskeleton and since the antennal gland i s located near the•anterior end of the animal only the anterior half of the animal was section-ed. This made f o r easier and better penetration of f i x a t i v e and wax. F i x a t i o n was i n 5$ formaldehyde, embedding was carried out by the dioxan wax process, the sections were stained i n Harris's haematoxylin and eosin, and mounted i n Canada balsam. A rough reconstruction of the gland was obtained i n the following manner. Each of a series of longitudinal sections of the gland was drawn on separate sheets of thi n tracing paper. The outline of the gland i n each drawing was then inked, the sheets were soaked i n x y l o l and p i l e d up over a lighted tracing table. The x y l o l made the paper transparent so that the inked outlines of the gland could be oriented i n the correct p o s i t i o n on top of one another. With the drawings stacked, 3 holes were punched through from top to bottom to serve as points of reference on each sheet of paper. A contour drawing of the gland was then made by tracing the outlines onto a sheet of tracing paper as though the sections of the gland were superimposed on each other. The three holes were used to orient the drawings for t h i s procedure. Reconstructions of the antennal gland by thi s method were made f o r both Neomysis and Mysis r e l i c t a . 40. The reconstruction by the described method of the antennal gland of Mysis r e l i c t a gave res u l t s c l o s e l y comparable to those of Vogt (1933) whose work was not obtained u n t i l after the above reconstruction was f i n i s h e d . It appears that t h i s simple method i s reasonably r e l i a b l e . [Resuits. > > " (> The antennal glands are paired organs l y i n g l a t e r -rally i n the antero-ventral region of the animal. They are ''located ventral and l a t e r a l to the stomach and extend forward ("from a p o s i t i o n half way along t h i s organ into the bases of o cthe antennae. * The gland was found to be composed of three parts, an end sac, a convoluted tubular portion, and a bladder which opens to the exterior through a pore i n the base of the (antenna. The parts of the gland can be distinguished by the -structure of the walls. In the end sac the walls are thick /and infolded, i n the tubule they are t h i n and i n the bladder 4they are thick with no invaginations ( f i g . 8.). In a l l parts Ci vthe n u c l e i are very prominent, being large, oval and stained deep blue. C e l l outlines are not apparent, the walls of the forgan appearing to be formed of a homogeneous red staining tissue with n u c l e i scattered randomly throughout. Some tissue resembling that of the antennal gland was found just under the outer integument i n a region under the carapace ( f i g . 9.). This tissue may be compared with the section of antennal gland seen i n f i g . 10. 41. The antennal glands in M. r e l i c t a and Neomysis are similar in arrangement and form. The gland ia Neomysis how-ever appears to be somewhat larger and the convoluted tubule more coiled than in M. r e l i c t a . STOMACH CAVITY END SAC END SAC LEXDJ*/*-/A/TO CONlC(OLL/T£-Z> TueuLE 3LADD£fZ EXT£Tf2/0/S f i g . 8. Cross section showing 3 regions of l e f t antennal gland of N. mercedis. X 150. 42 f i g . 9. Longitudinal section showing tissue i n dorsal region of | #. f e r c e d i s resembling antennal gland tissue, x ZOO f i g . 10. Longitudinal section through bladder and part of convoluted tubule of antennal gland of N. mercedis. X 2.00 43. EFFECT OF ABRUPT SALINITY CHANGE Method Beakers containing water of c h l o r i n i t i e s 0.29 o/oo, 0.70 o/oo, 1.11 o/oo, 3.15 o/oo, 5.19 o/oo, and 10.33 o/oo (control) were set up i n a constant temperature water bath, at 5°C. Ten to twelve Neomysis from a c h l o r i n i t y of 10.33 o/oo were placed i n each beaker and the times to death noted. When t h i s experiment was repeated the same c h l o r i n i t i e s were not used but a comparable range was established. E s s e n t i a l l y i similar r e s u l t s were obtained. Results F i g . 11 represents graphically the res u l t s of t h i s experiment. The survivals at various times (5» 7, 9,and 15 days) are plotted against the test c h l o r i n i t i e s . Survival was i r r e g u l a r (note curve f o r 5 days) t i l l about 7 days. At t h i s time greatly increased mortality occurred i n the lower s a l i n i t i e s . As time progressed m o r t a l i t i e s i n higher s a l i n i t -i e s occurred (curves moving to l e f t ) . This would seem to indicate that a c h l o r i n i t y of approximately 1 o/oo (bend of curve f o r 7 days) exerts a l e t h a l e f f e c t on Neomysjs from 10.33 o/oo c h l o r i n i t y . Continued exposure to c h l o r i n i t i e s somewhat higher than t h i s w i l l also cause death but because of the time taken f o r death to occur i t i s suggested that factors other than low s a l i n i t y may be contributing to the e f f e c t . 44. f i g . 11. Percent s u r v i v a l of Neomysis (from 10.33 o/oo c h l o r i n i t y ) exposed to a range of c h l o r i n i t i e s . 45. EFFECT OF GRADUAL SALINITY CHANGE  Method Fresh water was siphoned slowly from a 2000 cc. Erlenmyer f l a s k into a beaker containing 10 to 12 crustacea i n environmental water. The flow was regulated by clamping the rubber siphon hose; i t could be cut down to about 15 drops per minute. When the Erlenmyer was emptied ( i t took approximately 12-18 hours) a water sample f o r c h l o r i n i t y test was taken .from the beaker, the Erlenmyer was r e f i l l e d and the experiment continued. Results -Figures 12 and 13 depict the r e s u l t s of the gradual s a l i n i t y change experiment. Here the rate of decreasing c h l o r i n i t y and the rate of m o r t a l i t i e s of Neomysis are shown together. In one case ( f i g . 13) the i n i t i a l drop of chlor-i n i t y was greater but i n both instances greatly increased mortality occurred after the c h l o r i n i t y had dropped to about 1 o/oo. F i g . 12 indicates some mortality (up to 40%) even i n the higher s a l i n i t i e s . A suggested explanation of t h i s i s that the animals used had been kept i n the laboratory about f i v e weeks. The condition of some of them may thus have been affected causing a greater s u s c e p t i b i l i t y to en-vironmental change. Notwithstanding t h i s e f f e c t i t i s noted that a greatly increased rate of mortality occurred after the c h l o r i n i t y had dropped to about 1 o/oo. 46, o r-S U N * -o o o >-» SHI M O SS • • H l r \ X, o x; o U N cu i x e n PC o 55 O a. 8-T o U N H uv| C M / / I * CHLORINITY —e — T 1 — I — 10 fig..12. 4 TIME DAYS Curves showing rate of mortality increase with rate of c h l o r i n i t y decrease. o U N o «-| O IN-in M O <x O U N _) ad o U N | « CM >« H t-f i-3 rH at o E-« O s-1 U N - | CN. 0 4 U N U N - | CM X CHLORINITY 1 : i 6 5 10 TIME — DAYS f i g . 13. Curves showing rate of mortality increase ;with rate of c h l o r i n i t y decrease. 47. EFFECT OF CHANGE FROM VARIOUS SALINITIES INTO FRESH WATER  Method, Col l e c t i o n s on March 17 were made at the mouth of the r i v e r ( i n Mud bay —3.63 0 / 0 0 fcl.), a short distance upstream (I.69 0 / 0 0 <cl.), 3 to 3^ - miles upstream (^chlorinity n e g l i g i b l e ) , 4^ miles upstream ('chlorinity n e g l i g i b l e ) , and 9§ miles upstream ('chlorinity n e g l i g i b l e ) . Individuals from each of these locations were placed i n beakers of fre s h water and the times to death noted. Results The bargraph i n f i g . 14 indicates the r e s u l t s of the t e s t . Repetition produced similar r e s u l t s . It i s shown that the animals c o l l e c t e d farther up the r i v e r survived longer i n f r e s h water. This indicates the p o s s i b i l i t y that these animals may be conditioned to lower s a l i n i t i e s . Such conditioning presumably occurs over a f a i r l y long period of time i f the r e s u l t s of the other s a l i n i t y t o l -erance experiments are accepted. It w i l l be remembered that the crustaceans showed no tolerance to c h l o r i n i t i e s lower than 1 0 / 0 0 even when the s a l i n i t y was decreased gradually. SALINITY PREFERANCE The experiment i s designed to show whether or not the crustaceans show a t t r a c t i o n to or avoidance of f r e s h water. 4 8 . 4- MI. UP - i $ MI*:JP 43 MI. UP 94 MI* UP MOUTH <..6 O/OOCL, 1,'? O/OO NUG'-dLE NEG'BLE N3G»3LB CL. CI,^ C L . C L . f i g . 14. Time to $0% mortality' of^Neomy^is^j^r^edis. from various locations when put In fresh water, Apparatus The apparatus was similar to that used by Erickson Jones (1949) in, his experiments on the reaction of f i s h to toxic substances. It consists of a glass tube (24" long x 1" dia.) with an i n l e t i n each end and 2 outlets about 2" apart i n the middle. Two large j a r s are used as resevoirs from 4 9 . which the solutions to be used are siphoned. One jar con-tained environmental s a l t water and the other f r e s h water. The s a l t water ran into one end of the tube, and out one of the outlets i n the middle. A similar course was followed by-f r e s h water entering from the other end of the tube. This arrangement served to provide 2 separate types of water with mixing occurring only i n the middle of the tube. Method Neomysis were introduced into the apparatus and s a l t water was run i n from both ends. Half an hour l a t e r observations of the positions of the animals were begun and carr i e d out. every 2 minutes f o r 20 to 30 minutes. The s a l t water was then shut off from one end and f r e s h water run i n instead. After half an hour observations were again carried out. F i n a l l y t h i s arrangement was reversed so that the s a l t and f r e s h waters were made to flow i n from the other ends. Observations were again made after a period of 30 minutes. The period of half an hour was allowed before taking observations i n order to l e t the animals s e t t l e down. Note was taken of the number of Neomysis i n each end and i n the middle of the tube. The "middle" comprised that region between the outlets where mixing occurred. By Injecting a small amount of methylene blue into the i n l e t s a comparison of the rate of flow from each end was obtained. The dye also served to indicate whether or not layering of f r e s h on s a l t water occurred. Since no s t r a t i f i c a t i o n was observed when 50. the tube was less than half f u l l , a l l tests were made under t h i s condition. Results The r e s u l t s of t h i s experiment indicated that M. mercedis from the mouth of the Nicomekl r i v e r ( c h l o r i n i t y 10.33 o/oo) showed no preference f o r f r e s h or s a l t water. At least there was no tendency to move toward or away from f r e s h water. The experiment did demonstrate that the Crustacea are p o s i t i v e l y rheotaxic. It was noted that when the animals were i n a current of water they moved against i t , consequently the greatest concentrations of animals were found most often at the extreme ends of the apparatus (the i n l e t s were i n the ends). If the flow was cut o f f , the animals at that end of the tube would gradually spread out so that there would be more or les s even d i s t r i b u t i o n throughout a length of the apparatus. Starting the flow from one end caused an eventual concentration of animals at that end. F i g . 15 indicates the altered d i s t r i b u t i o n i n the apparatus caused by switching the inflow from one end to the other. This diagram represents the re s u l t s of one of the t r i a l s . The experiment was repeated four times with comparable r e s u l t s . In the test described animals happened to be almost evenly d i s t r i b u t e d at the sta r t of the experiment. (In some t r i a l s an uneven d i s t r i b u t i o n occurred at the s t a r t , i t then remained t h i s way u n t i l the flow was altered.) The even d i s -t r i b u t i o n remained u n t i l the 8-minute mark when the flow was stopped at the r i g h t end. By 16 minutes the animals were d i s t r i b u t e d i n the middle and l e f t end of the tube. At 18 minutes the flow was started i n the ri g h t end and stopped i n the l e f t . By 26 minutes some of the animals had moved back across the tube to the right end. The trial.'-was d i s -continued after 26 minutes but the trend towards the right end i s evident at t h i s time. 52. TIME STAH1 xt. 5 ; 0 WATER FLOW WATtiK FLOW 1 0 - ^ 0 VT^TTTr^ r^777/ 1 0 0 1 0 r-* 0 Q 1 0 5-0 10 '" - 5 0 9 10 5-0 a— iO -5 0 1 2 , i t CO ^ o 1 < CO -5 S >-> o s 16 :3 10 ^7777777777^Z^>x 10 >3 ST. -5 0 Q x § i o • 0 ^ 10 B 0 7 2 1 0 «J -0 777T7 / 7 T T T T T 7 / / / / / / T T T T ^ ^ 1 0 • 5 0 2 6 10 5-0 -«f 1 0 _ c 0 / / / / / / / / / / / / / / / ' • / , / / / // / / // // / FHESH WATiiR MIXTURE SALT WATER f i g . 15. Chart Indicating distribution of N^_mercedis (cross hatched areas) in apparatus with change of water flow. Additional description in text, 53. D i s c u s s i o n The d i s t r i b u t i o n s of N. mercedis on the P a c i f i c coast of North America indicates the extent of euryhalinity exhibited by t h i s species. It might be compared with Neomysis  vulgaris which i s also a brackish water mysidacean widely di s t r i b u t e d i n European waters. This species has been taken i n the open sear and Elton (1936) found the species i n loch Barvas More, a shallow, f r e s h water lake close to the seat i n -the I s l e of Lewis, Outer Hebrides. He reports that the Crustacea are well established and i n s u f f i c i e n t numbers to be an important trout food. The f a c t that N. mercedis i s found i n the Nicomekl and Serpentine r i v e r s from the mouths upstream to regions of f r e s h water r a i s e s the question of how and why such a d i s -t r i b u t i o n occurs. To adequately answer the question of "how" w i l l require an extensive study of the physiology of the animal's osmoregulatory and locomotory mechanisms. Some contribution to the problem of "why" has been brought out by t h i s study. S a l i n i t y experiments and the d i s t r i b u t i o n of the species show i t to be capable of a high degree of osmoregulation, other s a l i n i t y experiments demonstrate the rheotaxic tendency of the crustaceans, and t h e i r i n a b i l i t y to d i s t i n g u i s h f r e s h from s a l t water. 54. The a b i l i t y to osmoregulate allows the animals to penetrate waters of low s a l i n i t y and rheotaxis causes them to move upstream, which movement i s not impeded by the presence of f r e s h water since i n experiments they have shown no a b i l i t y to d i s t i n g u i s h i t from s a l t water. The combination of these c h a r a c t e r i s t i c s probably accounts f o r the d i s t r i b u t i o n of Neomysis^rom the s a l t water of Mud bay to the fresh waters of the Nicomekl and Serpentine r i v e r s . It was remarked that Neomysis were noticeably more abundant i n October and November than i n any of the following months i n which c o l l e c t i o n s were made. Several explanations may be offered. The c o l l e c t i o n s of October and November were pre-dominantly of females carrying developing young i n th e i r brood pouches. These c o l l e c t i o n s were made i n locations sheltered from the d i r e c t force of the r i v e r current. It i s suggested that females congregated i n these sheltered areas temporarily to release the young. T a t t e r s a l (1938) suggested that i n some species of marine Mysidacea, breeding females rose to the surface when young were ready to be l i b e r a t e d . Another explanation i s based on the fa c t that p r e c i p i t a t i o n and runoff i s much greater i n the f a l l and winter. This e f f e c t combined with that of high tides during these seasons r a i s e s the r i v e r l e v e l greatly so that collections were hampered. Since c o l l e c t i o n s were made by using a dip net on the end of a six foot pole, high water prevented the c o l l e c t o r from reaching areas which had hitherto proven 55. well populated. Although t h i s f a c t o r may have contributed somewhat i t i s concluded that there was an actual decrease i n the population either through death or translocation. In support of t h i s view i s the f a c t that a bottom drag net, operated i n a l o c a t i o n which had previously shown abundance of mysids with the dip net, yielded only a few i n d i v i d u a l s . Further, the increased runoff greatly increases the amount of f r e s h water on top of the underlying layer of sea water above the flood gates. With t h i s increased volume of f r e s h water there i s a greater chance that Neomysis w i l l move into i t (experiment has shown they are not repelled by f r e s h water) where death w i l l occur i f they remain long enough. Even i f they remain only t i l l l osing powers of m o t i l i t y they would then sink and be carried downstream on the ebbing t i d e . While summer c o l l e c t i o n s may throw more l i g h t on the problem of apparent decrease i n abundance, the r a i s i n g of the r i v e r l e v e l i n the winter undoubtedly has an important e f f e c t . According to the growth analysis the animals mature and breed i n a year, some however probably l i v e 1^ years to breed a second time. Indications are that two reproductive periods occur, one i n the f a l l the other i n the spring, so that two populations, half a year out of phase, exist together. Since each female c a r r i e s only 2 0 to 3 0 young and breeds but once a year the reproductive p o t e n t i a l of Neomysis i s low compared with other crustaceans. (The c r a y f i s h , 56. Cambarus a f f i n i s . bears 200—400 eggs, Storer, 1943.) Even with t h i s low p o t e n t i a l the animals were very abundant i n the Nicomekl during the early f a l l i n d i c a t i n g they are par-t i c u l a r l y suited to th e i r environment i n the estuary of t h i s r i v e r . So f a r as can be discovered, no work has been done on the range of temperature tolerance of invertebrates which would be comparable with the re s u l t s of t h i s study. There are many records of the l e t h a l temperatures of invertebrates but evaluations of o v e r a l l thermal tolerance have been evaded. The method of treatment i n t h i s study was patterned after that used by Fry and his associates who worked mainly with f i s h . Comparisons can accordingly be made with t h e i r r e s u l t s . The thermal tolerance of Heomysis mercedis was found to be 491 units, and t h i s may be compared with that of the speckled trout, Salvelinus f o n t i n a l i s ? — 6 2 5 units (Fry, Hart, and Walker, 1946); the bullhead, Amelrus nebulosis.—1160 units (Brett, 1944)} the goldfish , Carassius auratus.—1220 units (Fry, Brett and Clawson, 1942). In a l l cases the lower l e t h a l temperature was 0°C. By using t h i s method a f a i r l y clear picture of the temperature r e l a t i o n s of animals may be presented. For the greatest c l a r i t y the upper and lower l e t h a l temperatures should be stated along with the units of thermal tolerance, so that some idea of the animal's a b i l i t y to acclimate as well as i t s resistance to temperature change may be obtained. 57. There was an i n d i c a t i o n that smaller i n d i v i d u a l s survived high temperatures better than larger ones* Fry (1946) found no s i g n i f i c a n t difference i n the a b i l i t i e s of small and large speckled trout, S a l v e l i n i s f o n t i n a l i s T to withstand high temperatures. He suggests however that the f i s h he used were nearly of the same age. Gunter (1947) found that small anchovys, Anchoa m i t c h e l l i diaphana T and s i l v e r s i d e s , Minidia berylinna peninsulae. survived cold better than larger animals. Huntsman and Sparks (1924) report that the resistance of f i s h to temperature extremes diminishes as the size increases. The reasons f o r t h i s difference between large and small animals i n surviving temperature extremes are as yet unknown, however, i t i s suggested that i n the case of Neomysis the larger individuals are approaching the l i m i t s of t h e i r l i f e span which may i n some way account f o r their reduced resistance. There has been a suggestion that Mysis r e l i c t a T the f r e s h water Mysidacean, w i l l breed only at temperatures below 7°C. (Samter and Weltner, 1904). It i s possible that a temp-erature l i m i t a t i o n may s i m i l a r l y a f f e c t N. mercedis. The h i s t o l o g i c a l examination showed a s i m i l a r i t y between some subexoskeletal tissue l y i n g under the carapace and that of the antennal gland. It i s considered that the tissue under the carapace may be involved i n r e s p i r a t i o n . Lang (1891) mentions that i n some Crustacea, including 58. members of the Malacostraca. the inner wall of the carapace, remains soft and i s used i n the resp i r a t o r y function. Since g i l l s are reported to be active i n osmoregulation, and since t h i s tissue resembles tissue of the antennal gland which also i s claimed to have an osmoregulatory function i t i s possible that both the gland and t h i s suggested respiratory tissue are concerned i n the osmotic mechanism of Neomysis. Although no d e f i n i t e measurements were made, re-construction of sectioned material and microscopic examination of the s l i d e s seemed to indicate the convoluted tubular portion °£ Neomysis antennal gland to be longer and more c o i l e d than that of Mysis r e l i c t a . According to Krogh (1939) the opposite of t h i s might have been expected. He reports, " i t seems to be a general rule that the n e p h r i d i a l organs are better developed and have a longer n e p h r i d i a l canal i n f r e s h water Crustacea than i n related marine forms". (The terms 'nephrid-i a l canal' and 'convoluted tubule' both refer to the same part of the gland.) Perhaps the f a c t that N. mercedis i s a brackish water species and capable of existence i n f r e s h water accounts f o r i t s well developed nephridial.canal. It i s reasonable that i n a form inhabiting an environment of wide s a l i n i t y range the organ of osmoregulation should be f a i r l y complex. The s a l i n i t y experiments indicated that Neomysis from a c h l o r i n i t y of 10.33 o/oo could tolerate c h l o r i n i t i e s down to about 1 o/oo while f i e l d observations have shown the animals to be present i n f r e s h water. Other s a l i n i t y exper-iments show that acclimatization to low s a l i n i t i e s and therefore 59. to f r e s h water must take some time to occur. This i s perhaps not surprising considering the f a c t that the organs concerned i n osmoregulation are suggested to be the antennal glands and the body surface, thus an increasing a b i l i t y to regulate osmotically would l i k e l y be dependent on a gradual change i n these structures. This type of acclimatization where an i n d i v i d u a l can, over a period of time, adjust to environmental changes may be referred to as phy s i o l o g i c a l acclimatization. It would seem that Neomysis can to some extent adjust osmotically i n th i s fashion. However there i s also genetic acclimatization which operates by selection and i t i s l i k e l y that t h i s i s the mechanism which allows those animals i n the upper, f r e s h water regions of the Nicomekl and Serpentine r i v e r s to survive. This would be associated with the rheotaxie tendencies of the crustaceans which cause them to move up into the regions of fresher water. The contention i s that the rheotaxis causes the animals to move into regions of low s a l i n i t y or fresh water where selection operates, producing a variety capable of existence i n t h i s environment. Transferring Neomysis from various s a l i n i t i e s to fr e s h water showed that even though taken from regions of ne g l i g i b l e c h l o r i n i t y those animals from such regions i n the lower reaches were unable to survive i n f r e s h water. Apparently Neomysis are sensitive to s a l i n i t i e s lower than can be determined by chemical t i t r a t i o n . (Beadle and Cragg, 194-0, found that Gammarus duebeni t a brackish water species can 60. survive so long as there i s a trace of s a l t i n the water.) This f a c t i s important from a p r a c t i c a l point of view. It indicates that Neomysis. although e x i s t i n g i n water of s a l i n -i t y too low to be determined chemically, s t i l l may be k i l l e d i n what i s known as f r e s h water. Apparently the only way to determine whether c e r t a i n water i s l e t h a l to the animals i s by subjecting them to i t ; a c t u a l l y t h i s was done with Neomysis from the loc a t i o n 94 miles upstream. They were put i n a beaker of water from the f i s h pond on the west side of the University campus. In t h i s environment 71% survived f o r 4 weeks, a t which time the experiment was discontinued. It was considered that mortality after t h i s time would not be due to the i n a b i l i t y to adjust osmotically. The following i s a short discussion on the p r a c t i c a l application of the findings i n this study. The f a c t that the Crustacea feed on plant and animal material of a type which i s available i n f r e s h water indicates that food should be l i t t l e or no problem to them i n th i s type of environment. There i s some i n d i c a t i o n that they are d e t r i t u s feeders. If t h i s i s so then, could they be established i n a lake, they would l i k e l y contribute much to the feed available f o r f i s h . It has been suggested that i f the animals feed l a r g e l y on secondary feed (e.g. copepods, cladocerans) then introducing them would serve no useful purpose as f a r as increasing the food supply i n a lake f o r f i s h . The argument 61. i s that such organisms add but another l i n k to the food, chain and a c t u a l l y reduce the weight of food material because of the energy expended i n extablishing t h i s extra l i n k . However, from the f i s h e s * viewpoint i t would seem that much less energy i s expended i n obtaining s u f f i c i e n t food of t h i s larger size than i n acquiring the smaller organisms. Con-sequently more energy i s available f o r growth. Col l e c t i o n s from the Nicomekl indicated that, compared with winter and spring, greatest abundance of Neomysis occurred i n the early f a l l . Also noted was the f a c t that females were bearing young at t h i s time of the year. These findings indicate that i f c o l l e c t i o n s are to be made for transplanting purposes then September and October l i k e l y constitute the best times f o r the c o l l e c t i o n s . It was suggested that the majority of animals l i v e f o r a year and reproduce once during that time. Apparently some ind i v i d u a l s survive the following winter ( l i v i n g 1^ -years) and reproduce a second time i n the spring. The largest number of eggs observed on a female was twenty-six. Indications are that females bear between twenty and t h i r t y young. This appears to be a f a i r l y low reproductive poten-t i a l , consequently a lake stocking program would necessitate the introduction of large numbers of animals i n order that the population may become established. Temperature experiments indicate the upper l e t h a l temperature of Neomysis to be 23°C. This may be compared with that of Kamloops trout f i n g e r l i n g s , (Sal mo gairdneri 62. kamloops Jordan, which Black (195D found to be 24°C. fox" animals acclimated to 11°C. Fry, Hart and Walker (1946) found 25.3°C. to be the ultimate upper l i m i t f o r Speckled trout, Salvelinus f o n t i n a l i s . A comparison with temperatures i n two oligotrophic lakes may also be made. Paul lake, a boarderline oligotrophy showed i n August a surface temperature of 20°C. with a bottom temperature of 4.4°C., Larkin et a l (1951). Kootenay lake, an oligotrophic type had a surface temperature of 19GG. and a bottom temperature of 4°C. i n June. It would appear that although the thermal tolerance of Neomysis i s somewhat lower than that of trout i t s upper l e t h a l l i m i t i s s t i l l above the temperatures of lakes i n which i t may be introduced. The suggestion that temperature acclimation i s f a i r l y rapid should be considered i f transplanting i s under-taken. If there i s a large difference of temperature (10°C. or more) between the place of introduction and location of c o l l e c t i o n , holding the crustaceans f o r a time at an i n t e r -mediate temperature i s advocated. The work on s a l i n i t y tolerance showed that Neomysis taken i n the lower reaches of either the Nicomekl or Serpentine r i v e r s are unsuitable f o r lake introduction. It was also indicated that conditioning these animals to fr e s h water would be a lengthy process and not p r a c t i c a l l y f e a s i b l e . However, i t was demonstrated that animals from the upper reaches (8 or 9 miles upstream) could survive i n fresh water thus in d i c a t i n g 63. the obvious l o c a t i o n f o r c o l l e c t i o n s . The foregoing indicates that Neomysis mercedis taken from the upper reaches of the Nicomekl or Serpentine r i v e r s would be able to adapt themselves to conditions and survive i n some types of f r e s h water lakes, and that once established they would add to the type of food sought by f i s h (mainly t r o u t ) . It i s r e a l i z e d , however, that l i v i n g organ-isms do not always react according to the predictions made fo r them, and that man when tampering with the natural d i s -t r i b u t i o n of animals can too e a s i l y overlook f a c t s which may prove v i t a l . I t i s suggested, therefore, that before large numbers of Neomysis are "dumped" i n a lake there be a prelim-inary introduction i n an enclosed area so that an estimation of the success or f a i l u r e of the proposed operation can be made. 64. SUMMARY 1. Neomysis mercedis was found to be d i s t r i b u t e d from s a l t to f r e s h water i n two r i v e r s . 2. It feeds on plant, animal and possibly d e t r i t u s material. 3. Growth to maturity i s suggested to take one year with some ind i v i d u a l s l i v i n g one and a half years. Breeding occurs i n the f a l l and possibly the spring. 4. The thermal tolerance of Meomysis was found to be 491 units ( i n square degrees centigrade) with lower and upper l e t h a l temperatures of 0°C. and 23GC. respectively. Temperature acclimatization was found to occur f a i r l y r a p i d l y . 5. C h l o r i n i t y of 1 o/oo was observed to be the lower l e t h a l s a l i n i t y l e v e l f o r Neomysis from water of 10.33 chlorinity. Acclimatization to s a l i n i t y change was suggested to be a slow process. 6. Neomysis exhibited no preference f o r s a l t or f r e s h water, ?• Neomysis did exhibit a rheotaxic tendency. ACKNOWLEDGEMENTS It i s a pleasure to g r a t e f u l l y acknowledge the assistance received i n carrying out t h i s work. Dr. W. S. Hoar, under whose d i r e c t i o n the study was made aided me with the photomicrography and was available at a l l times to give advice, c r i t i c i s m and assistance. To him i s due my special a p p r e c i a t i o n Thanks are also to be given to Dr. W. A. Clemens f o r his c r i t i c i s m s and assistance i n arranging the material; to Dr. A. H. Hutchinson f o r his help i n the ident-i f i c a t i o n of stomach contents; to Dr. P. Ford f o r his suggest-ions and help i n the h i s t o l o g i c a l reconstruction work; and to Dr. P. A. Larkin v/ho was primarily responsible f o r the under-taking of the study and who has shown a stimulating i n t e r e s t at a l l times. My personal f r i e n d , Ross Johnson, assisted me i n f i e l d c o l l e c t i o n s , i n taking experimental readings, i n measur-ing the animals, i n c r i t i c i z i n g various phases of the invest-igation and i n extending encouragement at a l l times. To him I express gratitude. To Mrs. Merva Cottle who allowed me the use of her h i s t o l o g i c a l stains and to my fellow students f o r t h e i r c r i t i c i s m s and advice, I am greatly indebted. F i n a l l y , to my wife, I wish to express appreciation f o r assistance i n making drawings f o r the h i s t o l o g i c a l recon-struction and f o r typing the several drafts of t h i s work. LITERATURE CITED BANNER, A. H., 1951. Letter to author dated A p r i l 2, 1951. BEADLE, L. C , and J . B. CRAGG, 1940. Studies on adaptation to s a l i n i t y i n Gammarus spp. I Regulation of blood and tissue and the problem of adaptation to f r e s h water. J . Exp. B i o l . , 1Z: 153—163. BEHR, E. H., 1918. An experimental study of acclim-ation to temperature i n Planaria  dorotocephala. B i o l . B u l l . , 3£: 277—317. BLACK, E. C , and V. S. Black, 1951. Upper l e t h a l temperatures f o r f i v e species of B r i t i s h Columbia f r e s h -water f i s h e s acclimated at 11°C. Manuscript copy. BORRADAILE, L. A., and F. A. POTTS, 1935. The Invertebrata. MacMillan Co., New York. BRETT, J . R., 1941. Tempering versus acclimation i n the planting of speckled trout. Trans. Am. F i s h . Soc,20: 397—403. 1 9 4 4 . Some l e t h a l temperature r e l a t i o n s of Algonquin park f i s h e s . Pub. Ont. F i s h . Res. Lab., 63. 1—49. CHACE, F. A., Jr.,1949. Letter of June 3, 1949, to Dr. P. A. Larkin. DAVENPORT, C. B., 1908. Experimental morphology. 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D i f f e r e n t i a l rate of death f o r large and small f i s h e s caused by hard cold waves. Science, 106: 472. 1949. The use of p r o b a b i l i t y paper f o r the graphical analysis of polymodal frequency d i s t r i b u t i o n s . Journ. Mar. B i o l . Assoc., 28: 141—153. 1927. Quantitative study of the changes produced by acclimatization i n the tolerance of high temperatures by f i s h e s and amphibians. B u l l . U. S. B. P., 4J:Part 2: 169—192. and MI I. Sparks, 1924. Limiting factors f o r marine animals. 3. Relative resistance to high temperatures. Contr. Can. B i o l . N. S. 2: 95—114. 1918. Acclimatization as a factor a f f e c t i n g the upper thermal death points of organisms. J . Exp. Zool., 22: 427—442. 1939. Osmotic regulation i n aquatic animals. Cambridge Univ. Press. 1891. Text book of comparative anatomy. Part 1. MacMillan & Co. London and New York. LARK IN, P. A., 194-8. Pontop'oreia and Mysls i n Athabaska, Great Bear and Great Slave lake s Fish.*Res. Bd. Can., B u l l . 78. LARKIN, P. A., G. C. ANDERSON, W. A. CLEMENS, and D. C. G. MACKAY, 1950. The production of Kamloops trout (Salmo g a i r d n e r i i kamloops,J ord an)in Paul lake, B r i t i s h Columbia. S c i e n t i f i c Publications of B. C. Game Dept. No. 1. LIENEMANN, L. J.,1938. The green glands as a mechanism fo r osmotic and ioni c regulation i n the cr a y f i s h (Cambarus c l a r k i i , Girard) J . C e l l , and Comp. Physiol., 27: 149— 161. LOEB, J . and H.WASIENEYS, 1912. On the adaptation of f i s h (Fundulus) to higher temperatures. J . Exp. Zool., 12: 543—557. MARSHALL, E. K., J r . and H. W. SMITH, 1930. The glomerular development of the vertebrate kidney i n r e l a t i o n to habitat. B i o l . B u l l . , 58—59: 135—153. PANNIKAR, N. K., 1941. Osmoregulation i n some Palaemonid prawns. Journ. Mar. B i o l . Assoc., 25: 317—359. PROSSER, C. L., D. W. BISHOP, F. A. BROWN J r . , T. L. JAHN, and V. J . WULFF, 1950. Comparative animal physiology. W. B. 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B i o l , and F i s h . 8: l 8 l — 205. 1938. The seasonal occurrence of Mysids off Plymouth. J . Mar. B i o l . Ass., Plymouth.,23: 43— 56. VOGT, W., 1933. Uber die Antennendruse, von Mysis r e l i c t a . Zool. Jahr. Abt. fur Anatomie. 56: 373—386. WIGGLESWORTH, V. B., 1933. The function of the anal g i l l s of the mosquito l a r v a . J . Exp. B i o l . , 10: 16—17. 

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