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Effect of egg size on size and viability of newly hatched medaka (oryzias latipes) and surf smelt (Hypomesus… Stanley, Richard David 1977

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THE EFFECT OF EGG SIZE ON SIZE AND VIABILITY OF NEWLY HATCHED MEDAKA {Orj^ias l a t i n e s ) AND SURE SWELT (Hypomesus £ret io s u s pret iosus) , By RICHARD DAVID STANLEY B.Sc,, U n i v e r s i t y o f B r i t i s h Columbia, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF THE FACULTY OF GRADUATE STUDIES (Dept. of Zoology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY CF BRITISH COLUMBIA A p r i l , 1977 MASTER OF SCIENCE i n Richard David Stanley, 1977 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced d e g r e e at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f ~^To /o The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date AfuJl /r/7 7 i i ABSTRACT The relationship between egg size and l a r v a l v i a b i l i t y , as inf e r r e d from size at hatching, resistance to starvation, and growth, was studied i n the Medaka, Orj^zias l a t i o e s (Temminck and Schlegel) , and the Surf Smelt, Hffpomesus ^ r e t i c s us pretiosus {Girard). Medaka larvae which hatched from heavier eggs were larger at hatching, but did not survive longer during starvation. When the larvae were fed a small and varied food, neither r e l a t i v e growth rate nor r e l a t i v e body depth was correlated with o r i g i n a l egg weight. However, when larvae were fed a large mobile prey, Paramecia multimicronucleatum, the larger the egg they came from the faster they grew. Thus, the advantage of large size at hatching i s p a r t i a l l y a function of the feeding conditions at hatching. In Surf Smelt, egg weight was correlated with maternal age. Two-year-old females produced eggs that were 50% heavier than those of one-year-old females, and hatchlings that were heavier and almost 1 mm longer. Smelt larvae with the most yolk reserve (yolk vol/length^) at hatching survived longer, and the amount of reserve was correlated with egg dry weight. The larvae f a i l e d to feed i n the laboratory. The e f f e c t of egg size on l a r v a l growth suggests that uncontrolled v a r i a t i o n in egg s i z e would affect experimental r e s u l t s , and may be important i n commercial fishery management. i i i TAEIE OF CONTENTS Abstract i i Table Of Contents i i i L i s t of Tables i v L i s t of Figures v Acknowledgements v i i I. Introduction 1 II. Methods ......10 A. The Medaka ... 10 B. The Surf Smelt .....15 I I I . Results 19 A. The Msdaka 19 B. The Surf Smalt ., 31 IV. Discussion 43 A. Discussion of Medaka Results 44 B. Discussion of Smelt Results .. 51 C. The Interaction Between Egg Size and Egg Number 54 D. Implications for Fishery Management 57 E. Future Studies 60 V. Conclusions 62 Literature Cited 64 i v LIST OF TABLES Table 1. Medaka. Larval Measurements ............... . 12 Table 2. Paramecia Density |/ml) 14 Table 3, Smelt. Larval Measurements ................. 17 Table 4. Medaka. Ccmpariscn of size at hatching and size after 4 days of feeding {20/inl) *•*#•••** »#•* ##»• •##» *« • 27 Table 5. Medaka. ccmpariscn of size after 4 days (starvation and 2/ml) .................. 28 Table 6. Medaka. Comparison of size at hatching and size after 4 days of feeding (infusoria) 29 Table 7, Smelt. Newly Hatched larvae. Correlation c o e f f i c i e n t s between l a r v a l size and egg size ........................... 38 Table 8. Smelt. 11 to 12-day-old larvae. Correlation c o e f f i c i e n t s between l a r v a l size and egg size ........................... 39 V LIST OF FIGURES Figure 1. Medaka. Mean length at hatching ............ 21 Figure 2. Medaka, Dry weight at hatching ............. 21 Figure 3, Medaka. i l l larvae, survival after hatching ................ ^  .......... 22 Figure 4, Medaka. Mean su r v i v a l time vs. dry egg weight 22 Figure 5, Medaka. Log length vs. log egg dry weight (hatch vs. 20/ml) 23 Figure 6. Medaka. Larval dry weight at hatching and after 4 days (20/ml) .................... 23 Figure 7. Medaka. Larval dry weight after 4 days (starving and 2/ml) .............. .... . . ... , . 24 Figure 8, Medaka. Larval dry weight at hatching and after 4 days (infusoria) ................ 24 Figure 9. Medaka. Relative body depth at hatching 25 Figure 10. Medaka. Relative body depth (20/nl) ........ 25 Figure 11, Medaka, Relative body depth (starvation and 2/ml) ........................ 26 Figure 12, Smelt, Cry egg weight vs. female length , 32 Figure 13. Smelt. Length at hatching .................. 33 Figure 14. Smelt. Larval dry weight at hatching 33 v i Figure 15, Smelt. Y c l k - o i l globule volume at hctlzclvxncf *#• ••**#*••**«*«••***•***••*••••••« • 3U Figure 16. Smelt. Length, 11 to 12 days old 36 Figure 17, Smelt, Dry weight, 11 to 12 days old ....... 36 Figure 18. Smelt. Gape vs. length, 11 to 12 days old ..................... , . . . 37 Figure 19, Smalt. Survival after hatching ( a l l X ct X V 510 } • • * * * * • * ' • » •* * « •* •* * * • * * • • * * • • * • •*•*# * ^ 1 Figure 20. Smelt, Survival vs. yolk reserve at hatching 42 Figure 21. Medaka, Mouth size and P. mi] 1t i m i c r c n uc le at urn size ................. 49 ACKNOWLEDGEMENTS I would l i k e to thank Dr. Norman J, Wilimovsky for the funding and supervision of t h i s project. I would also l i k e to thank my committee f c r the i r help, p a r t i c u l a r l y Dr, Chitty, who, with my family, attempted tc incorporate the rudiments cf English grammar into t h i s thesis. f i n a l l y , and es p e c i a l l y , to Vicky Eutler and Bruce leaman, thank ycu for the encouragement and assistance during the ccurse of t h i s project. 1 I. INTRODUCTION F i s h eggs vary i n s i z e w i t h i n a p o p u l a t i o n and produce c o r r e s p o n d i n g l y v a r i a b l e l a r v a e (reviewed by N i k c l s k y , 1965; B l a x t e r , 196S; and Bagenal, 1973). S i z e at hatching may a f f e c t growth r a t e s and s u r v i v a l r a t e s , and, s i n c e l a r g e r f i s h produce l a r g e r eggs than do younger f i s h , the s t r u c t u r e c f the stock may a f f e c t egg s i z e , s i z e at hatching and a l l t h a t goes with i t , i n c l u d i n g v a r i a t i o n s i n abundance of the s t o c k . T h i s paper l o o k s at some c f these i n t e r r e l a t i o n s . I f l a r v a l v i a b i l i t y changes with egg s i z e w i t h i n s t o c k s , then egg s i z e i s o b v i c u s l y r e l e v a n t to f i s h e r y management, s i n c e recruitment i s thought to be l a r g e l y determined during e a r l y l a r v a l l i f e {Hjort, 1914; Bevertcn, 1962; G u l l a n d , 1965; Hempel, 1965; K i k c l s k y , 1965; Cushing, 1S69). Eresumably t h i s i s the stage most a f f e c t e d by egg s i z e v a r i a t i o n . However, f i s h e r y managers normally pay l i t t l e a t t e n t i o n to the e f f e c t s of q u a l i t a t i v e v a r i a t i o n i n the spawn of marine f i s h . Most models and s t o c k - r e c r u i t s t u d i e s i n c o r p o r a t e a d u l t stock s i z e s o l e l y as adult or egg abundance. Can v a r i a t i o n i n egg s i z e e x p l a i n some of the v a r i a t i o n i n r e c r u i t m e n t ? Schopka and Hempel (1S73) proposed that t o t a l egg mass be used as an index c f stock abundance. T h i s has the advantage of i n c o r p o r a t i n g the i n f l u e n c e of both egg s i z e and egg number. They assume t h a t egg weight and l a r v a l v i a b i l i t y are l i n e a r l y r e l a t e d . T h i s i s an important assumption and i t i s u s e f u l to examine what evidence supports t h i s assumption, and what i s the 2 h i s t o r y c f i t s d i s c u s s i o n . In 1887, F r a n c e s Day o b s e r v e d t h a t t h e l a r g e r e g g s o f " E u r o p e a n t r o u t " p r o d u c e l a r g e r f r y , and s u g g e s t e d t h a t s u r v i v a l i s c o r r e l a t e d w i t h s i z e a t h a t c h i n g . He d i d n o t t h i n k o f egg s i z e as an a d a p t a t i o n t o the i n c u b a t i o n and l a r v a l e n v i r o n m e n t , u u t as a d i r e c t f u n c t i o n o f m a t e r n a l growth r a t e c r s i z e . H i s o p i n i o n was l a t e r s u p p o r t e d by D a h l (1918) and Gray (1S26). S v a r d s o n (1949) combined Brown's wcrk (19 4 6 ) , which showed t h a t g r e a t e r s i z e i n a c o m p e t i t i v e f e e d i n g s i t u a t i o n c o u l d l e a d t o a g r e a t e r growth r a t e , w i t h examples o f d e n s i t y - d e p e n d e n t l a r v a l g r owth and s u g g e s t e d t h a t i n c r e a s e d s i z e a t h a t c h i n g c r e a t e s a c o m p e t i t i v e a d v a n t a g e . S v a r d s o n t h e n added t h i s s u g g e s t i o n t o L a c k ' s (1947) a d a p t i v e i n t e r p r e t a t i o n o f c l u t c h s i z e i n b i r d s , and s u g g e s t e d t h a t t h e d i v i s i o n o f r e p r o d u c t i v e mass i n f i s h e s i s a t r a d e - o f f between q u a n t i t y and q u a l i t y . S v a r d s o n t h e r e f o r e d i s c u s s e d t h e a d v a n t a g e o f r e l a t i v e s i z e d i f f e r e n c e s , but he i g n o r e d t h e p o s s i b i l i t y t h a t s i z e d i f f e r e n c e s a t h a t c h i n g can be r e l a t e d t o a b s o l u t e d i f f e r e n c e s i n v i a b i l i t y . E x c e p t i n t h e c a s e o f i n t e r s p e c i f i c c o m p e t i t i o n , a c o r r e l a t i o n between r e c r u i t m e n t and egg s i z e depends on t h i s a b s o l u t e r e l a t i o n s h i p . M a r s h a l l (1953) n o t e d t h a t f i s h s p e c i e s t e n d t o have b i g g e r eggs a t h i g h e r l a t i t u d e s , and s u g g e s t e d t h a t l a r g e l a r v a e have an a d v a n t a g e o v e r s m a l l l a r v a e i n : (1) h a v i n g s m a l l e r f o o d r e q u i r e m e n t s per gram body w e i g h t ; (2) swimming f a s t e r ; (3) h a v i n g l e s s i n t r a s p e c i f i c c o m p e t i t i o n ( b e c a u s e f e w e r l a r v a e a r e h a t c h e d f r o m a g i v e n biomass) 3 (4) being better competitors; (5) hatching in a more advanced state, Marshall's f i r s t statement i s based on Zeuthen's (1949) observations cf invertebrate oxygen consumption over size variations of 2 to 3 orders of magnitude, More recently Minberg (1960), in a review which included l a r v a l f i s h , suggested that respiration in f i s h e s could be represented as: Q = 0.3 Eeighto-*. fin exponent of less than 1,0 agrees with Marshall's statement. 1 However, Ciechomski (1966), working with anchovy, Enqraulis anchoita Hubbs and Marini, and Blaxter and Hempel (1963), working with d i f f e r e n t herring stocks, Clujaea harengus Linnaeus, found that, within stocks, larger larvae were not appreciably more e f f i c i e n t . Marshall's second statement assumes that l a r v a l swimming speed i s proportional to length. although this has been shown to be the general case, the experiments have confounded size and age (Eyland, 1962; Hunter, 1972). The importance of small differences in age i s shewn in Hunter's work, in which a dramatic difference in feeding occurred with 1 or 2 days difference in age. S i m i l a r l y , Theilacker and Lasker (1974) have shown that predation on anchovy larvae by a euphausiid shrimp (Euphcusia pacifica) decreases rapidly with an increasing l a r v a l age. These e f f e c t s may be the r e s u l t of experience, but they 1 Bicker (1973) has suggested on the basis of "functional regression" analysis that 0.85 i s a better estimate of the exponent. a may also be caused by added physiological or morphological maturity, which would aff e c t swimming speed. Marshall's t h i r d statement seems in c o r r e c t . There would be fewer larvae, but the biomass would be the same. Without s i g n i f i c a n t differences in digestive e f f i c i e n c y or feeding a b i l i t y , the demand for food would be v i r t u a l l y equal, and the demand might be directed to a point higher in the trophic web, where food would be scarcer or more d i f f i c u l t to catch. Marshall's fourth statement e x p l i c i t l y extends Svardson's discussion to i n t e r s p e c i f i c competition. I t s t i l l leaves unanswered the question whether larger larvae might be f i t t e r on an absolute basis Marshall's f i n a l point i s that a large egg might f a c i l i t a t e further development (as occurs i n higher l a t i t u d e s , where the period of incubation i s long and the l a r v a l phase short). However, t h i s i s a separate response, and t h i s theory does not explain the s i t u a t i o n where egg size variation simply changes the scale of size at hatching. Marshall's f i r s t and second statements seem to be the only ones applicable to variation within marine pelagic stocks. Although no rel a t i o n s h i p has yet been established, large size may provide a feeding advantage through a c o l l e c t i v e e f f e c t of greater swimming speed (cruising or striking) and a larger irouth or digestive t r a c t . If feeding increases d i r e c t l y with body weight, and metabolism increases as postulated by Winberg, then r e l a t i v e growth would be correlated with body size at hatching. In addition to giving feeding advantages, greater size at hatching may decrease predation because the larvae are too fa s t 5 or, are too big to be eaten by s p e c i f i c predators, Kerfoct (1974) examined a cladoceran, Bosmina I c n g i r c s t r i s , and suggested that seasonal egg size variation i n t h i s invertebrate species was caused by s i z e - s p e c i f i c predation upon the instars. S i m i l a r l y , Lenarz and Hunter (BS) , and Ware (1975) , suggest that predation may partly account for the tendency of egg size to vary inversely with temperature (Bagsnal, 1971). At a lower temperature, and the resultant slower development, a change i n size at hatching w i l l result i n a large absolute difference i n the time required for the larvae to reach a s p e c i f i c length - a delay which increases the chance of predation. At higher temperatures, development i s so rapid that small size at hatching becomes les s detrimental, as the larvae reach the s p e c i f i c length so quickly. The authors, however, assume that predation i s constant with temperature, and furthermore Ware assumes that larvae of equal size have the same mortality rates regardless of age, A t h i r d p o s s i b i l i t y i s that the proportion of yolk may change with egg size. Marshall reported that egg siz e increases with increasing la t i t u d e and that the eggs become "yol k i e r " . The added yolk may allow a longer development period and thus greater maturity at hatching, or, i f incubation time remains constant, i t may allow the larvae to hatch with more yolk reserve and thus be able to survive periods cf low food abundance. Blaxter and Hempel (1963) have shown the l a t t e r to be the case in a comparison of herring stocks. In summary, i t has been suggested that the importance of 6 increased size at hatching i s related to predation, feeding, and resistance to starvation. Given the d i f f i c u l t y i n experimenting with these phenomena, i t i s readily apparent why experimentation has been r e s t r i c t e d to starvation and growth. To my knowledge, no studies other than those in model form have examined whether the size variation at hatching within a f i s h stock can a l t e r predation rates upon the larvae. Resistance to starvation at hatching has received the most attention (Bagenal, 1969a; Blaxter and Hempel, 1963; Ciechcmski, 1966). These studies have shown that, within a stock, larvae from larger eggs may survive s i g n i f i c a n t l y longer, but the absolute differences, i f present, are very small. This led the authors to conclude that egg size variation within t h e i r stocks would not affect abundance. The a b i l i t y of larvae to withstand starvation i s a limited i f not irisleading c r i t e r i o n of v i a b i l i t y . If the most common feeding s i t u a t i o n i s low food abundance and not t o t a l absence, s u r v i v a l time under starvation would be enhanced by any combination of added yelk reserves and reduced a c t i v i t y or metabolism. But, i n the presence of abundant food the l a t t e r two features may be disadvantageous. If reduced energy consumption were a viable s u r v i v a l t a c t i c the larvae should reduce a c t i v i t y as prey density decreases, yet the opposite i s true (Wyatt, 1972). Therefore, feeding should be examined to assess the effect of size at hatching on s u r v i v a l . That the feeding a b i l i t y may be the c r i t i c a l aspect of s u r v i v a l i s supported by the r e s u l t s of l a r v a l rearing experiments, Many attempts to raise marine larvae have f a i l e d , 7 with t o t a l mortality occurring whan the larvae make the t r a n s i t i o n to external feeding (reviewed by May, 1970). The explanation for this phenomenon has often been that the food conditions were i n s u f f i c i e n t q u a l i t a t i v e l y or guantitatively. Subtle changes i n feeding a b i l i t y might s i g n i f i c a n t l y a f f e c t t h i s d i f f i c u l t period i n l a r v a l l i f e . S i m i l a r l y , the tendency for egg size to be greater in l a t e spring or summer stocks has been explained i n terms of l a r v a l feeding. Hempel (1965) claims that there i s selection against the production of small larvae during late f a l l and winter, when food conditions are poor. A few people have studied the r e l a t i o n between size at hatching and growth. The usual experimental design has involved r a i s i n g salmonid fry in hatchery conditions with prepared food (Dahl, 1918; Bagenal, 1S69b; E i l t o n , 1970) or carp fry i n aguaculture ponds (Kirpichnikov, 1966; Hulata, Moav, and Wohlforth, 1S16) . Over the short term, the r e l a t i v e size differences at hatching remain and over the long term, the absolute differences tend to disappear except under competition. Increased size at hatching seems to provide only a "head-start," Although t h i s e f f e c t i s of interest t c fishery models, because early l a r v a l mortality i s assumed to be inversely related to p a r t i c l e size (Jones and H a l l , 1974; Ware, 1 9 7 5 ) , i t seems an excessive jump to suggest that t h i s e f f e c t on s u r v i v a l would be noticeable i n comparison with those of other variables such as temperature, predation, or food abundance and d i s t r i b u t i o n . A more profound influence could be expected i f r e l a t i v e growth rate or feeding a b i l i t y were a function of size at 8 hatching. From a modelling standpoint, the more rapid growth rate would further reduce the time spent as a small p a r t i c l e . A s l i g h t increase in searching capacity or feeding a b i l i t y would reduce a larva's probability of starvation (Ivlev, 1965). The conditions of the e a r l i e r experiments minimized the t h e o r e t i c a l advantages of large size at hatching. The prey was presumably i n excess, and in the salmonid experiments, non-mobile and of a size that even the smallest f r y could eat without d i f f i c u l t y . I nterestingly, Dahl reports the use of l i v e food, "freshwater-crustaceans," and his data show that the f r y from larger eggs grow faster. Unfortunately, he includes the means without the variance, and he obtains the two egg sizes by using two genetic stocks. Variation in s i z e at hatching presumably af f e c t s l a r v a l v i a b i l i t y . However, i t i s not known whether the r e l a t i v e l y small variations observed within populations are of valid concern to a fishery manager. If s i z e at hatching a f f e c t s early su r v i v a l and f i n a l abundance, then the impact of added size might be mediated through d i f f e r e n t i a l feeding in the early l a r v a l stage. This e f f e c t would have l i t t l e c orrelation with how long a newly hatched larva can r e s i s t s tarvation, nor with how well a larva can feed on prepared food* This paper therefore examines whether small variations in size at hatching which occur naturally in a f i s h population could a f f e c t feeding on an active, mobile prey during the t r a n s i t i o n to external feeding. 9 Questions: 1. How are small differences i n size at hatching correlated with l a r v a l growth or condition when the larvae are fed an active, mobile prey? 2. Is the impact cf size at hatching on feeding p a r t i a l l y a function of prey density? 3. How i s a b i l i t y to withstand starvation cn the part of newly hatched larvae correlated with a b i l i t y to feed? 10 II. METHODS I examined the eggs and newly hatched larvae of two f i s h species: the Medaka, Oryzias l a t i p e s (Temminck and Schlegel); and the Surf Smelt, Hypomesus jgretiosus _p_retiosus (Girard). A. The Medaka The medaka were obtained in May 1974, from the Nagoya Aguarium Company, Nagoya, Japan. Unless s p e c i f i e d otherwise, the experiments i n t h i s study were conducted on adults obtained i n the o r i g i n a l shipment. Non-breeding adults were maintained at a low temperature (16°C±2°C) and a short phctoperiod (8 hours l i g h t , 16 hours dark). They were fed once daily with a dry flake preparation ("Tetramin"), To stimulate and maintain breeding, the f i s h were subjected to a higher temperature (25°C±1°C) and a longer photopericd (16 hours l i g h t , 8 hours dark). They were fed four times a day: twice with dry food, and twice with frozen brine shrimp. During peak breeding, the females daily produced broods of 5-50 eggs within an hour of the onset of l i g h t . The f e r t i l i z e d eggs, attached to the female by numerous filaments, were removed with a curved glass rod and placed in a p e t r i dish f i l l e d with water. I found that extensive handling of the eggs in the f i r s t hours aft e r f e r t i l i z a t i o n led to increased egg mortality. 11 Therefore, I l e f t the eggs for 6-8 hours, divided the broods in half, and discarded the u n f e r t i l i z e d or abnormal eggs. I estimated brood egg size by calculating the dry weight of half the eggs in a brood. The eggs were dried in a desiccator for 3 days at room temperature, and then weighed to 0,01 mg (s.d. = 0,005 mg) on an electrobalance. The remaining half of each brood was incubated i n a p l a s t i c weighing boat in a solution of 99.89% d i s t i l l e d water, 0,1$ rock s a l t , and 0.01$ methylene blue. Each "incubation boat" was floated in a water bath of 25.5°C±.5°C. The eggs received 16 hours a day of fluorescent l i g h t (1000-5000 lux) and 8 hours of darkness. Most eggs hatched on the ninth day a f t e r f e r t i l i z a t i o n . The remaining eggs were temperature-shocked by f l o a t i n g the incubator boats i n a 28°C water bath for 30 minutes, Only those eggs that hatched on the ninth day were used. Newly-hatched, 2-day- and 4-day-old larvae were fixed i n 10% formalin for 2 days and then measured with an ocular micrometer (Table 1). I measured gape width in anaesthetized larvae. The bones were transparent, but the movement of the lower jaw allowed me to c l e a r l y i d e n t i f y the hinges. After measurement, the larvae were dried in a desiccator and weighed to the nearest 0,001 mg. A medaka larva at hatching weighed approximately 0.140 mg (s.d. cf measurement = 0,002 mg). Larvae which were kept a l i v e for feeding and starvation experiments, were placed in 500 ml of well-water i n 1400-ml jars. The j a r s , blackened to water-level, were set in a 25°C 12 TABLE 1 Medaka. Larval Measurements Feature | _ j. Magnif,| (x) | i,. Units | (n) | Description | Length | T 1 and 2 | 20 | 0.050 | Anterior t i p of jaw to | days old j 1 i posterior t i p of notochord | 4 days | 15 | 0.067 ] (as above) ^ | Body | 30 j 0,034 | Dorsal-ventral musculature j depth | depth, above the anus | Mouth | 400 | 0.0034| Inside width of mouth | gape | between hinges of upper | and lower jaws | (anaesthetized specimens) | L._ i _ 13 water bath under a daily 16-hcur photoperiod of fluorescent l i g h t (12000-14000 lux). I fed a large species of Paramecium, Paramecia mul t i micro nu cleat turn, (180u x 60u) to newly hatched medaka, and I attempted to maintain one of three feeding regimes in each j a r : 2, 20, or 200 paramecia per ml. Fifteen larvae were placed i n each feeding jar. whenever possible, a l l were taken from one brood. To increase the sample number in some cases I had to use mere than one brood. Eroods were combined only when the mean brood egg weights differed by less than 0.006 mg. The weighted mean was used as the representative egg weight for those samples. I maintained a culture of P, multimicronucleatum•and used i t to stcck i n i t i a l densities in the jars. To control densities of food after i n i t i a t i o n , I drew 450 ml twice da i l y from each j a r , and replaced i t with paramecia and well-water to make up the correct density and volume. Samples from the jars indicated that actual feeding densities varied considerably from the expected levels (Table 2), In view of t h i s variation i t i s obviously incorrect to consider feeding densities in absolute terms. However, frequent changes of medium would prevent any sustained bias, and the r e l a t i v e differences would remain, A commercially prepared l a r v a l f i s h food ("Liguifry") was intended as a second food source. Instead of the i n i t i a l inoculum cf paramecia, 3 drops cf the preparation were added to the jars. One drop was added to each j a r , three times daily for the following four days. I observed larvae feeding upon the preparation at f i r s t , T A B L E 2 Parametria Density {/ml) I T— T ' 1 — T j Expected j Observed | Samples | Standard D e v i a t i o n | | Density | Mean I I I I I Density J | | | 2 j 1.3 | 28 | 1.8 j | 20 | 30.7 J 16 | 20.7 I l 200 J 284.6 I 44 j 1 5 5 . C l L 1 'X L , 1 1 5 but shortly after being put i n the chamber, the preparation disappeared to a point undetectable under lew power (40x). This process was assisted by swirling the jars each time food was added. The suspended nutrients led to a culture of protozoans smaller than 50 mu. B. The Surf Smelt Adult smelt were obtained from a commercial fisherman i n Puget Sound in October 1915. They were seined on the north shore of Liberty Bay, 100 meters southeast of the North Kitsap Marine Science Center, Paulsbo, Washington. l i v e females were taken from the net and sampled immediately. A sample of u n f e r t i l i z e d eggs from each female was placed in 5% formalin. The remaining eggs were removed from each female and placed on submerged glass plates (20x17cm), The eggs attached themselves to the plates by a chorionic adhesive cup. Each plate cf eggs (corresponding to an i n d i v i d u a l female) was immediately f e r t i l i z e d with the milt from two males. The glass plates were placed upright and p a r a l l e l i n a wooden rack, and submerged in sea water (11-15°C). Air stones were placed in a row perpendicular to the plane of the plates, which caused the water to c i r c u l a t e vigorously between the plates. The eggs were l e f t i n darkness, except when I was examining them or changing the water. After 18 days of incubation, the plates were exposed tc a i r daily for 35 minutes in order to stimulate hatching. Larvae 16 kept for determination of hatched size were preserved within 24 hours cf hatching. Larvae kept for rearing experiments were allowed to accumulate over a 48-hour period, in order to produce s u f f i c i e n t sample sizes. Newly hatched and 11- to 12-day-old larvae were fixed in 10% buffered formalin for one month, and then measured and weighed (Table 3), The yolk volume was calculated from horizontal and v e r t i c a l measurements of the yolk and o i l globule. The o i l globule occupied a small proportion of the yolk volume, fitter measurement, the larvae were dried and weighed (as was dene with the medaka). The larvae kept a l i v e for feeding experiments were maintained in 9 - l i t r e , black, p l a s t i c buckets. These were set in a water bath of 9-12°C, and covered with black p l a s t i c , except for a c i r c u l a r hole, 15 cm i n diameter, cut from the center of the cover, The cover around the l i p prevented illumination of the wall of the bucket. The larvae tended to remain in the center of the bucket, a habit that reduced the incidence of abrasions on the bucket wall (J. Marliave, pers. comm.). Each bucket was gently aerated, The larvae were illuminated 16 hours daily with fluorescent l i g h t i n g (12,000 lu x ) . One 10-watt incandescent bulb shone above a l l tanks (1-4 lux) during the dark period. There were three feeding regimes: starvation, "lew," and "high". The l a t t e r two groups were fed daily with marine plankton, which had been caught in a 54-mu net tewed 1-3 metres below the surface. The plankton was strained through a 4G0-mu sieve, and then divided volumetrically among the "high" and 17 TABLE 3 Smelt. Larval Measurements Feature | Magnif. ! (x) | On i t s j I (mm) | Details Length I 1 day I 14 | 0.050 | anterior t i p of lower jaw to posterior t i p cf 11-12 I 13 | 0.0667 | notcchord Body J 100 | 0.0136 | dorsal-vantral musculature depth j j | depth midway between the yolk-sac and anus Yolk | 40 I 0.034 | Length and height axes ! i i Mouth | 400 I 0.0034 | Maximum outside width of gape ] ] | lower jaw 18 "low" buckets, at a r a t i o of 10:1. Diameter, wet weight, and dry weight measurements for each brood were taken from u n f e r t i l i z e d eggs. Individual egg diameter was calculated as the mean of two perpendicular diameter measurements (50x magnification), Brood egg diameter was calculated as the mean diameter of 40 eggs, Wet egg weight was calculated from eggs that had been covered with a fine nylon mesh, blotted to remove surface moisture, and then weighed i n groups of 200 to the nearest 0.01 mg. The eggs were then dried for 24 hours at 60°C, allowed to cool i n a desiccator, and weighed, I calculated the error i n the egg weights, wet and dry, from 3 sequential samples from 6 females. Each cf the 18 samples was then sub-divided to make three samples of 200 eggs. After the eggs had been removed, each female was preserved in 105? formalin and la t e r examined for length, weight, and age. I used scales, o t o l i t h s , and length freguency to determine age. 19 III, BESUITS A. The Medaka The dry weight of medaka eggs varied between 0.17 and 0.31 mg/egg. This range in size i s similar to that in the examples given by Nikolsky (1965) i n which variation was associated with d i f f e r e n t female age groups. The medaka egg range i s equal to, or less than, the variation observed by Bagenal (1973) i n 32 freshwater and marine species. The range i s si m i l a r to that given by Shirota (1970) for 40 species. Egg weight was not related to female s i z e , although larger females produced more eggs. Egg mortality was low for most egg sizes i<5%), although the heaviest eggs had a s l i g h t l y higher mortality. The proportion of eggs that hatched on the ninth day of incubation tended to decrease with increased egg weight, To prove that egg dry weight of half a brood was representative of brood egg dry weight, I f i r s t examined the variation among brood portions. The c o r r e l a t i o n c o e f f i c i e n t among groups of f i v e eggs from one brood was 0,92 (n=32), Among groups of 8 eggs i t was 0,93 (n=28). The high correlations suggested to me that the variation within broods was net so great as to negate the i n f e r e n t i a l estimate of the egg dry weight of those larvae to be raised. The small difference i n co r r e l a t i o n c o e f f i c i e n t s between groups of 5 and 8 eggs indicates that using half the eggs from broods of d i f f e r e n t numbers would not res u l t in s i g n i f i c a n t error. 20 The r e l a t i o n s h i p between egg d r y w e i g h t and l a r v a l s i z e a t h a t c h i n g i s shown i n F i g u r e s 1 and 2. The l e n g t h - e g g w e i g h t r e l a t i o n s h i p b e s t f i t s an e x p o n e n t i a l f u n c t i o n i n which t h e e x p o n e n t i s s i g n i f i c a n t l y l e s s t h a n 1,0 ( l o g L e n g t h = l o g a + b l o g H e i g h t ) ( T a b l e 4 ) . L e n g t h , a o n e - d i m e n s i o n a l measurement, would p r e s u m a b l y v a r y w i t h e i t h e r t h e s g u a r e r o o t (egg c i r c u m f e r e n c e , b=0,5) o r t h e cube r o o t (egg d i a m e t e r , b=0.33) c f egg d r y w e i g h t . The e s t i m a t e o f b i s l o w e r t h a n b o t h t h e s e v a l u e s , p o s s i b l y b e c a u s e s m a l l e r eggs t e n d t o h a t c h s c c n e r , o r , i f a r t i f i c i a l l y s t i m u l a t e d , t e n d t o h a t c h l a r v a e i n a more mature s t a t e , and t h e r e f o r e p r o p o r t i o n a t e l y l o n g e r . L a r v a l d r y w e i g h t a t h a t c h i n g was l i n e a r l y r e l a t e d t o b r o o d egg dry w e i g h t , which g i v e s t h e i m p r e s s i o n o f g r e a t e r s i z e v a r i a t i o n t h a n does t h e g r a p h o f l e n g t h . The a b i l i t y o f newly h a t c h e d medaka l a r v a e t o w i t h s t a n d s t a r v a t i o n i s shown i n F i g u r e 3. F i g u r e 4 shows t h e i n f l u e n c e o f egg s i z e on b r o o d s u r v i v a l . An a n a l y s i s o f v a r i a n c e i n d i c a t e s s i g n i f i c a n t v a r i a t i o n among b r o o d s , b u t none o f t h i s v a r i a n c e i s e x p l a i n e d by v a r i a t i o n i n egg s i z e . The f e e d i n g r e s u l t s a r e shown i n F i g u r e s 5 t o 11. The inedaka s t o p p e d b r e e d i n g b e f o r e s u f f i c i e n t s a m p l e s c o u l d be c o l l e c t e d f o r t h e 200/ml t r e a t m e n t . The l o g - l o g r e g r e s s i o n s o f l e n g t h on egg w e i g h t were not s i g n i f i c a n t l y d i f f e r e n t among f e e d i n g t r e a t m e n t s . F i g u r e 5 i s i n c l u d e d t o show t h e c hange from h a t c h i n g , and to show t h a t , a f t e r f o u r d a y s o f f e e d i n g , l e n g t h r e m a i n s c o r r e l a t e d w i t h o r i g i n a l egg w e i g h t . F i g u r e s 6, 7, and 8 a r e g r a p h s o f mean l a r v a l d r y w e i g h t a g a i n s t egg d r y w e i g h t . I have p l o t t e d t o g e t h e r : ( 1 ) the 20/ml t r e a t m e n t and F i g u r e 1 kEDAKA * KGAN LENGTH AT HATCHING G.Q, S.&L 4.01 + 4*1- * + + ++ + t++ • + 4.oi + + + + H 1 1 1 r -o - i a o.ao o-ea o-E4 O-ES CSQ ERLXD EGG DRY WT« (MG/EGG) MEDAKA Y = 0 . 0-171 Figure 2 / DRY WEIGHT AT HATCHING 3 E - 0 1 + 0 - 4 0 0 5 k X N = 0.151 o-iaL + + o-oaL + + + O-IB —I o.ao 0-E2 0-24 C25 0.23 B R U D EGG DRY WEIGHT (MG/EGG) MEAN SURVIVAL IN DAYS NUMBER o. o.. o.. o.. 01 ui cn co ca H ( - H 1 I H I 1 — I t to I H 1 I—i 15 H M 3i M 4 OP Si o 6 B - 8 - 6 8 8 S 8 8 l i ii ^ n .• .• .« .• ro ui cn m to 6" < 1 1 1 1 1 1 — H h 1 P. 3 TO n F i g u r e 5 KCDAKA LOG LENGTH V S - LOG EGG DRY WEIGHT (HATCH V S . ECU ML) 1.35. 2 0 / m l Hatch LOG EGG DRY WEIGHT F i g u r e 6 k - E D M A DRY WEIGHT At HATCHING AND AFTER 4 DAYS (2CVVL) 0.171 0.151 o . i a i O'lli 0.091 0-07. CIS 0.20 C22 0-24 0-2S 0-23 2 0 / m l Hatch 0-30 ERDJD EGG DRY WEIGHT (MG/EGG) F i g u r e 7 F/EDAKA LARVAL. DRY WEIGHT AFTER 4 DAYS (STARVING AND H/MJ 24 o.ia. 0.171 CIS! o-iaL O-lil cosl C07. 2/ml S t a r v e d 0-18 0-20 0-22 0*24' CcS 0-28 0-30 BR0QL3 EGG DRY WEIGHT CMG/EGG) F i g u r e 8 N^HAKA LARVAL DRY WEIGHT AT HATCHING AND AFTER 4 DAYS (INFUSORIA) 0.19 0.17. 0.07. 0-25 BRDDO EGG DRY WEIGHT (MG/EGG) Hatch Infusoria F i g u r e 9 MEDAKA RELATIVE BODY DEPTH AT HATCHING 25 0-105^  o.ceo. 0.C75I 0.0951 + 0-065. 4f + + + + + + - + — 1 1 — ) 1 1 0-1B 0-30 0-22 0-24 O-EE 0.2B C30 BRCTO EGG CRY WEIGHT CMG/EGG) F i g u r e 1 0 MEDAKA RELATIVE BCDY DEPTH (3J/MJ 0-10S. O'lOQ. 0.075J. 0.1B 0-20 0-22 0-C4 0-2S 0-23 0-30 BRCCD DRY EGG WEIGHT (M3/EGG, 26 F i g u r e 11 MEOAKA RELATIVE BODY DEPTH CSTARV- ATO 2/MJ Q.1C5_ 0-070. 0-1B C E O 0-32 C « E 4 2 / m l O-EB o-sa C30 BROOD EGG DRY WEIGHT CMS/EGG) 27 TABIE 4 Medaka. Comparison of size at hatching with size after 4 days of feeding { 20/ml ) 1. Log length vs. Log egg dry weight T -Treatments Hatching 4 days eld ( 20/ml ) samples 42 14 slope prob. 0. 178 0.354 n, s, Intercept ( x=.21 ) prcb, 1. 44 •1. 57 < 0.001 — 4 2. Larval weight vs. Egg dry weight T — l Treatments j samples | slope prob, J Intercept ( x=.21 ) prob. | Hatching J 4 days eld J ( 20/ml ) | 42 | 14 | 0,483 1,265 < 0.01 | 0. 121 0. 110 n. s. j _ J . . _ L . . . J. 3. Relative body depth (arcsin d/1) vs. Egg dry weight Treatments Hatching 4 days eld ( 20/ml ) samples 40 13 slope prob. +— 0,033 0. 169 < 0.1 90% confidence l i m i t s of slope -0.029 to 0,095 0.087 to 0.254 28 TABLE 5 Medaka. Comparison of size after 4 days ( starvation and 2/ml ) 1. Log length vs. Log egg dry weight Treatments h 4 4 days old ( 2/ml ) < starv, ) samples 12 15 slope prob. Intercept ( x=.21 ) 0. 154 0. 150 n. s. prob. 1. 54 1, 52 n. s. -I 2. Larval weight vs. Egg dry weight Treatments | samples j slope prob, Intercept prob. ( x=,21 ) 4 days eld { 2/ml ) I 13 ( starv, )| 15 0.75 4 C.479 < 0,1 0. 084 0. 078 n. s. 3. Relative body depth (arcsin d/1) vs.„ Egg dry weight Treatments 4 days eld ( 2/ml ) ( starv, ) samples 13 16 slope prob. 0.176 0,045 < 0, 1 90$ confidence l i m i t s of slope 0.101 to 0.250 -0.029 to 0,119 L. J TABLE 6 Medaka. Comparison of size at hatching with size after 4 days of feeding ( in f u s o r i a ). 1 . Log length vs. Log egg dry weight Treatments h J | Hatching I J 4 days eld j ( infus. ) samples 32 10 slope prob. 0.091 0.417 n. s. Intercept prob, { x=,21 ) 1 . 44 1. 53 < 0.00 1 2, Larval weight vs. Egg dry weight | Treatments f J Hatching j 4 days old | { infus, ) samples 13 10 slope prob. C. 506 0. 53 8 n.s. Intercept prob. ( x=.21 ) 0. 118 0. 112 n.s. J. X - L J. | 3. Relative body depth (arcsin d/1) vs. Egg dry weight i ! j Treatments | samples i ! f _i J 4 days eld | 12 j ( infus. ) | slope | 90% confidence I l i m i t s of slope 0,101 | -0,070 to 0.270 t. 30 data of newly hatched larvae (Figure 6); (2) the 2/ml and starvation treatments (Figure 7); and, (3) the i n f u s o r i a treatment with a second independent set of data for newly hatched larvae (Figure 8). Although only the means are plotted, the predictive regressions for a l l except the 2/ml treatment and the second set of hatch data are calculated from i n d i v i d u a l l a r v a l observations (multiple Y's for each X, Sckal and Echlf, 1969), In every case, the F s t a t i s t i c for deviations from l i n e a r i t y was s i g n i f i c a n t (deviations about the regression/within group v a r i a t i o n ) . This could result from curvature, or, more simply, from scatter of the means about the regression. The degree of curvature was not s i g n i f i c a n t f c r any of the l a r v a l dry weight calculations. The added variance can be explained in that the members of one or a pair of broods had more in common than egg size (for example genetic or chamber-induced variation) , A l l regression l i n e s are calculated from weighted means; because the sample sizes were egual, the l i n e s f i t the plotted means. The exception i s the infusoria treatment. The lim i t e d production of eggs, and my assumption that food would be well dispersed, and supplied i n excess, (thereby reducing the competition), led me to relax the condition of egual densities i n the jars. Thus, the l i n e based on weighted means appears to deviate from the plotted means. Figures 9, 10, and 11 are plots of r e l a t i v e body depth (arcsin depth/length) against egg dry weight. The regressions of the 2/ml and 20/ml treatments both exhibited s i g n i f i c a n t and positive slopes, The slopes of the newly-hatched, starved, and 31 i n f u s o r i a treatments did not d i f f e r s i g n i f i c a n t l y from zero. Tables 4, 5, and 6 show the regression and probability s t a t i s t i c s for the pairs of treatments. The probability calculations refer to the li k e l i h o o d that each pair of treatments has a common slope or intercept (one-tailed t e s t ) . The intercept i n each case i s calculated from an egg dry weight measurement cf 0.21 mg, which approximates the "small" egg size i n each sample. B. The Surf Smelt Egg dry weight i s plotted against maternal length in Figure 12, The two length modes correspond to 1-year- and 2-year-old females. Measurements from each brood of egg dry weight, egg wet weight, and egg volume were highly correlated: Dry weight - wet weight (n=22) r = 0.93 Dry weight - volume (n=22) r = 0.89 Wet weight - volume (n=22) r = 0.92 Egg diameter varied among broods from 0.98 to 1,22 mm. The brood standard deviations ranged from 0,021 to 0.043 mm. The r a t i o of dry weight to wet weight in the preserved eggs varied from 19$ to 24%, and was not correlated with egg size. Samples cf larvae less than 24 hours old were obtained from 21 broods. Figures 13, 14, and 15 i l l u s t r a t e the rela t i o n s h i p between egg dry weight and, l a r v a l length, dry weight, and yolk 32 7 , a r 7.0.. 6.7. G. G« s-a. s.s. F i g u r e 13 SMELT LENGTH AT HATCHING Q4B 12? -+- -t - -+- -+- -+- -+-20. 22. 24« ES« 28- 30« 32. 34« 3S» EGG DRY WEIGHT CMG/3D0 EGGS) 3 F i g u r e 14 o.is_ 0-14. c i a . 0-12 . c n . cio. coa. coa. C07. cos. cos. 0.04l_ 20. SMELT LARVAL DRY WEIGHT AT HATCHING 34 Vises p I 33 Tr-39 4 3 24 39 T T I 2H« 5 4 . ES. 28- 30- 3S« 34- 35. 3 B EGG DRY WEIGHT (MG/EOO EGGS) 34 0.12. F i g u r e 1 5 SMBJT YOLK-OIL GLCQJLE VOLUME AT HATCHING 3 0 o-cei H o . o s i d 0.041 Q i 0.021 33 3 P 37 H-G2 1 2 35 i4i 33 J 4 C B S O-OOi 20. 22. 24- 2S. 28- 30- 32. 34- 39. EGG DRY WEIGHT CMG/200 EGGS) 35 volume at hatching. Included are the mean ±1 standard deviation for each brood. The standard deviation was used to exhibit the natural variation, rather than the confidence l i m i t s of the means, which are p a r t i a l l y a function of sample s i z e . Egg dry weight was the best correlate of each body measurement (Table 7), and was used as the independent variable in the figures; but i n no case were the three correlates s t a t i s t i c a l l y d i fferent, I found no differences in l a r v a l size among the three feeding treatments, and therefore assumed that a l l larvae were starved, i n spite of the fact that larvae kept i n the high food treatment had exhibited feeding behaviour and had small amounts of food in t h e i r intestines on day four. I could obviously not f i n d out how feeding was affected by l a r v a l size at hatching, but I could examine the relationship between egg size and size at hatching at the time of yolk resorption. At the termination of the feeding experiment, 11 to 12 days after hatching, only 75% of the larvae had any y o l k - o i l globule remaining, and the reserve appeared to be predominantly o i l globule. These larvae are thus at the point in development when they must switch to external feeding; and, i f herring re s u l t s apply, i t i s the time when, in the absence of food, body si z e reaches a maximum (Elaxter and Hempel, 1963). Figures 16 and 17 show the relationships between o r i g i n a l egg size and l a r v a l length and dry weight after 11 to 12 days of starvation. The c o r r e l a t i o n c o e f f i c i e n t s are shown in Table 8. Figure 18 i s a plot of the mouth gape of 11- to 12-day-old larvae against length. The time t i l l death during starvation of larvae from a l l 7'3_ 7.0.. 6>7.. B-4.. G-i. s-e. S.H. s.si F i g u r e 16 SMELT LENGTH 11-12 DAYS OLD ^74 35 T 40 40 35 3^ IB EO. EE« •4 1 1 ! 1 1 E4« E6« 28" 30. 3S. 34. EGG DRY WEIGHT (MG/ECO EGGS) CiS^ o-ia. cie. 0«11. 0.10. o-oa. coa. C 0 7 . COG. COS.. 0-04. _ F i g u r e 17 SMELT LARVAL DRY WEIGHT 11-12 DAYS OLD 35 I 39 E5 IP I 30 EC EE. E4- ES- E8- 30- 3 H - 3 4 T EGG DRY WEIGHT (MG/200 EGGS) 37 Figure 18 SMELT GAPE V S » LEN3TH 1 1 - i E DAYS OLD Y = O 4 S 3 5 E - 0 1 + O4B20E-01*X N = 38 0.40_ o-sal 0-341 0-3=1 LENGTH 38 TABLE 7 Smelt, Newly hatched larvae. Correlation c o e f f i c i e n t s between l a r v a l size and egg s i z e . Feature Number of Broods 4 -f Log length Larval dry wt. Yolk Vol, Yolk/L^ 21 19 21 Egg size Dry wt. | Bet wt. | Diameter| Volume ,85 (log egg weight) .94 . 75 .46 . 80 (log egg weight) . 86 . 63 .35n,s. .84 . 80 . 46 14n.s. 39 TABLE 8 Smelt, 11- to 12-day-old larvae. Correlation c o e f f i c i e n t s between l a r v a l size and egg s i z e . Feature ] Number ! of | Broods r I I Log | 9 length J Larval j dry wt,j < Egg size Dry wt. . 79 (log egg weight) . 90 Set wt. , 88 (log egg weight) . 84 Diameter ,95 Volume .73 x 40 broods i s shown in Figure 19. The mean i s 18 days (9-13°C). I assumed that the mortality during the f i r s t few days was due either to handling or to congenital defects, and was not relevant to a study of starvation resistance. In the regression c a l c u l a t i o n s , I therefore excluded mortality observations prior to 7 days after hatching. This would be before yolk resorption and coincides with the 99% confidence l i m i t s of the o v e r a l l mean. Figure 20 shows the mean su r v i v a l of each brood (with standard deviation and sample s i z e ) , regressed against r e l a t i v e yolk reserve at hatching (yolk volume/length' 3). Length, raised to the power of 3.0, 3,5, or 4.0, was assumed to r e f l e c t weight (metabolic demand). The regression eguations were calculated as multiple y-valuss for each x. The regression of su r v i v a l against egg weight was not s i g n i f i c a n t . The regression of su r v i v a l against yolk reserve at hatching (with any cf the exponents) suggested s i g n i f i c a n t l y increased s u r v i v a l with increased yolk reserve. 41 F i g u r e 19 SMELT SURVIVAL AFTER HATCHING (ALL LARVAE) 3S-30 .1 ES-! 20.1 15. lO-I S.I -+- 4=L !• 2. 3. A. 5- G« 7. 8' 940.ili2 .13^4^4£.17.1B-iae0eL^a54^ese7^53l30 •AYS 24. F i g u r e 20 SMELT SURVIVAL V5- RESERVE AT HATCHING 22-1 20-1 lB-l 1S-1 14.1 12-i 30 51 4 3 I 10.1 -+- -+- •+- -+- -+-0-09 0'12 0-15 0-1B 0-21 0>24 YOLK-OIL GLDSLLE VOLUVE / LENGTH 0 . 2 7 43 IV. DISCUSSION In f i s h e s , egg size and subseguent size at hatching tends to increase with female age or s i z e . The average egg size produced by a stock might therefore be manipulated by a fishery manager as stock age and size d i s t r i b u t i o n i s affected by exploitation, It has also been shown that size at hatching i s proportional to egg s i z e . If one assumes that v i a b i l i t y varies with size at hatching, there are obvious conseguences for fishery management. Does egg size variation affect l a r v a l s u r v i v a l and ultimately abundance? 1 Large size at hatching could a f f e c t : (1) resistance to starvation; (2) feeding e f f i c i e n c y or a b i l i t y ; (3) v u l n e r a b i l i t y to predation. The previous experimental evidence is limited to stating that: (1) large eggs produce larger f r y or larvae; (2) the large f r y or larvae do not survive longer during t o t a l starvation; and (3) when fry are raised on high levels of prepared food, the difference i n size i s maintained only into early juvenile l i f e unless i n the presence of i n t r a - s p e c i f i c competition. The f a i l u r e to f i n d s i g n i f i c a n t stock-recruit relationships (Gulland, 1973) and the many unsuccessful attempts to raise marine larvae past the point of yolk resorption, have led researchers to f e e l that recruitment i n many fishes i s determined by food density and composition at the time of the t r a n s i t i o n to external feeding (Hjort, 1914; Cushing, 1974). The importance of size at hatching to v i a b i l i t y might be 44 assessed by examining i t s impact on l a r v a l feeding. Is the e f f e c t cf size at hatching more profound than i s implied by the ••head" s t a r t " suggestion? Is i t related to an improvement i n predatory a b i l i t y , i n which larger larvae could grow much fa s t e r , cr avoid starvation? Previous experiments tended to minimize the advantages of added size at hatching. If a larva were fed a large mobile prey, would increased size at hatching have a greater impact cn growth during the t r a n s i t i o n to external food? How w i l l prey density a f f e c t this r esult? A. Discussion of Medaka Results There was no c o r r e l a t i o n between egg dry weight and the duration of l a r v a l s u r v i v a l during t o t a l starvation, although the analysis of variance showed s i g n i f i c a n t variation among broods. As in other studies, i t appears that starvation resistance does not vary s i g n i f i c a n t l y with the egg size variation observed within populations. The range i n mean length (predicted by a log-log regression on egg weight) was approximately, 4.2 to 4.4 mm. Studies of marine f i s h larvae have shown s i g n i f i c a n t variation i n food items among size classes of 2 mm, and one study of mackerel and anchovies, has shown differences among 1.5 mm s i z e classes (Arthur, 1976), These studies, however, confounded size with age, as did the studies of swimming speed. I could f i n d nothing i n the l i t e r a t u r e to suggest that the length differences observed in the medaka would measurably a f f e c t feeding. 4 5 Egg size and v i a b i l i t y did not seem to be related. Length differences at hatching were very small, and while t h i s cculd be compensated for by greater yelk reserves, larvae from the larger eggs did not survive any longer. The next stage was to examine growth. As I was only interested in the t r a n s i t i o n to exogenous feeding, I examined the f i r s t four days after hatching. The high temperature and early mortality during starvation suggested a rapid t r a n s i t i o n to external feeding. Furthermore, the medaka larvae i n i t i a t e d feeding behaviour in the f i r s t day a f t e r hatching. The 2/ml density was shown to be a low food density, as dry weight decreased from that of hatching. However, the slope of the 2/ml treatment was s i g n i f i c a n t l y greater than that of the starved treatment (p < 0. 1 ) , although the intercepts were not d i f f e r e n t at the lower end of the egg weight range (Fig. 8). The larger larvae, therefore, appeared to have fed successfully. The 20/ml treatment was assumed, a p r i o r i , to be the intermediate food density, and to be the treatment in which si z e at hatching would have the greatest impact on growth. If added size tends to increase feeding a b i l i t y , the impact of added size may become less important as food conditions approach either extreme. Larvae from th i s treatment were heavier than the starved or 2/ml treatment larvae (Fig. 6), They were compared, therefore> with size at hatching. The slopes of the 20/ml and hatch regressions for l a r v a l weight were s i g n i f i c a n t l y d i f f e r e n t , but the intercepts at the lower end of the range were not. The larvae from smaller eggs incorporated enough food to 46 compensate for the consumption of yolk, The large larvae not only compensated for their yolk consumption, but increased approximately 259! i n dry weight, A dry weight difference at hatching cf 25% increased to a difference of 50Ss after only 4 days of feeding. The r e l a t i v e growth rate of larvae was therefore p o s i t i v e l y correlated with brood egg dry weight and size at hatching. The analysis of body depth supports the evidence for a relationship between size at hatching and feeding. This measure cf "robustness", suggested to be a va l i d index of condition (Wyatt, 1972), was p o s i t i v e l y correlated with egg size in the two paramecia feeding treatments, but i t showed no co r r e l a t i o n i n newly hatched or starved f i s h . I t i s possible that t h i s index i s not s p e c i f i c a l l y a measure of condition but of morphological maturity: the conclusions remain the same. After these experiments the adult medaka began to shew the e f f e c t s cf prolonged forced spawning. Egg production decreased and mortality increased, while examining a second species, I maintained the o r i g i n a l adults at a lower temperature and shorter photopericd, and raised some larvae to maturity. From t h i s combination of spawners, I obtained a limited egg production which allowed me to examine some aspects of my paramecia r e s u l t s . The basic guestion a r i s i n g from the previous experiments was: Why did larger larvae grow more rapidly? Presumably the answer to t h i s guestion would determine the generality of the r e s u l t s . The added egg size might be associated with some gu a l i t a t i v e difference not s p e c i f i c a l l y related to s i z e , i n which case one would expect greater growth by the larger larvae. 47 regardless of the food source. Or perhaps the advantage was a function of size , and would disappear i f the larvae were fed a small, inanimate food source at high densities as i n the salmonid experiments. I attempted to test these ideas by duplicating the o r i g i n a l design, except that I used a commercial food preparation ("Liguifry"), In t h i s treatment, the regression of l a r v a l dry weight was not s i g n i f i c a n t l y d i f f e r e n t in slope or intercept from that at hatching, and the regression of r e l a t i v e body depth was net s i g n i f i c a n t . The i n f u s o r i a data are highly ambiguous in that the actual food item i s unknown. Furthermore, the variance i s large, larger than i n the other treatments; presumably the cultures in each chamber did not develop at a uniform rate. The dry weight data suggest that the larvae did indeed feed, because their dry weight was greater than those of the starved and 2/ml treatments, But, since the regression was not diff e r e n t from that at hatching, and the regression of r e l a t i v e body depth on egg size was not s i g n i f i c a n t , the larvae from the larger eggs did not exhibit the same advantage as i n the paramecia experiments. This result agrees with those of Hulata, Moav, and Hohlfarth (1S76), who raised carp fry from d i f f e r e n t sized eggs i n aguaculture ponds. Presumably, the paramecia results were not due to some qu a l i t a t i v e variance merely associated with added s i z e . Furthermore, i f smaller eggs produced less viable larvae q u a l i t a t i v e l y , one might expect to see an eff e c t of added mortality in both the egg stage and the starvation experiment. I f feeding was primarily done on the infusorians, the reduced 48 growth (relative to the 20/ml treatment) would be due to the lag in the development time in the cultures. Infusoria density was very low in the cultures for the f i r s t two days, The infusoria experiment suggested that the advantage of the large larvae i n the paramecia treatments might be s p e c i f i c a l l y related to their larger size and the prey size, I therefore measured the gape of 4-day-old larvae. The range of gape width predicted from a regression of gape on standard length i s shown in Figure 21. Also shown i s the size range of P. -multimicronucleatum in length and diameter. As no simple technigue for measuring the v e r t i c a l gape during feeding was apparent, I plotted an underestimate- The v e r t i c a l gape in the diagram i s the extent of the opening during the weak respiratory movements under anaesthesia. Shirota (197 0) calculated the v e r t i c a l gape by assuming a mouth feeding angle of 50°. , This would result i n at least a doubling of the v e r t i c a l gape shown i n the diagram. Of the 34 species examined by Shirota, many of which were smaller i n length than the medaka, none had v e r t i c a l gapes less than 225 mu, which would be approximately the length of the largest paramecia, and 3-4 times the diameter. Mendiola (1974), working with very young anchovy larvae, found that p a r t i c l e size in the gut was well within the r a t i o of gape to prey width seen i n t h i s example (3:1), I do not think that the gape d i f f e r e n t i a l alone could account for the difference in growth. Perhaps the advantage i n growth i s the res u l t of the additive effect of added length at hatching on c r u i s i n g speed, attack speed, and gape. Or, i t might be a function of one character which changes d i r e c t l y with dry weight, for example 49 Larval medaka gape maximum and minimum width, predicted from a regression of width on body length (4 days old). 50 mouth volume. The suction power of the buccal-pharyngeal pump would presumably vary with dry weight, 2' 5u11imicrcnuc1eatum seems to be a reasonable food source for l a r v a l medakas, i n that a l l sizes of larvae fed successfully. However, small differences i n l i n e a r dimension at hatching were associated with a greater growth rate, and a more robust body shape, This difference appeared at both food densities. These observations support the theory that increased f i s h egg size and size at hatching i s p o s i t i v e l y correlated with v i a b i l i t y . I f added size leads to a f a s t e r growth during the t r a n s i t i o n to external feeding, and i f predation i s inversely related to body s i z e , then v i a b i l i t y i s p o s i t i v e l y correlated with egg size to a greater extent than i s predicted by assuming a growth model which i s d i r e c t l y a function of weight (Hare, 1 975) . An cider, simpler explanation states that l a r v a l survival depends e n t i r e l y on the food conditions at the time of yolk resorption. when food was e n t i r e l y absent, added l a r v a l size conferred no advantage. But at low food d e n s i t i e s , the larger larvae showed a d e f i n i t e advantage. Size at hatching could a f f e c t survival without incorporation of s i z e - s p e c i f i c predation upon the larvae. The medaka results suggest that small variations i n size at hatching can a l t e r early growth rate. Sp e c i f i c growth rate, and presumably s u r v i v a l on a single food item can be affected by small size variations at hatching. This suggests that the impact of added s i z e at hatching i s more profound than i s 51 represented by the simple head-start concept. The s e n s i t i v i t y between prey and predator size undermines confidence i n the extrapolation of l a r v a l rearing experiments. Growth and s u r v i v a l rates on e a s i l y cultured laboratory foods way not re l a t e to natural feeding conditions. Experiments which involve the rearing of marine larvae should consider the standardization of egg s i z e . Conversely, any attempt to assess the importance of size at hatching must pay p a r t i c u l a r attention to the food item. The present observations support a long-established theory (Hjort, 1914) that l a r v a l survival depends not only on the timing and abundance, but also on the d e f i n i t i o n cf the plankton. S i m i l a r l y , by indicating a s e n s i t i v i t y between l a r v a l s i z e and prey s i z e , they i n d i r e c t l y support the theory cf Jones and Hall (1974). Size at hatching within a stock may determine the number of previous-days production of those copepcdids accessible to the f i s h larvae. Starvation resistance i s seen as a limited c r i t e r i o n of v i a b i l i t y . B, Discussion of Smelt Results I attempted to examine similar guestions with a second species, the Surf Smelt. The use of smelt allowed a number of i n t e r e s t i n g changes to be made in the o r i g i n a l design. F i r s t l y smelt larvae would presumably feed i n a manner similar to that of herring and plaice. Both use a s p e c i f i c , methodical s t r i k i n g 5 2 behaviour, unlike the medaka larvae, which, for the f i r s t few days, appear to feed by a continuous, rapid series of snaps. The importance cf size at hatching might be influenced by the s p e c i f i c feeding behaviour cf the larvae. Secondly, I obtained eggs from females of d i f f e r e n t ages, Soviet work has shown that although young females can produce smaller eggs, the smaller eggs can exhibit a higher proportion of l i p i d s and proteins (Anokhina, 1968). Also, as I would have much larger samples from which to obtain egg size c a l c u l a t i o n s , I could examine which measurement of egg size was the best predictor cf l a r v a l size at hatching and growth. Bagenal (1969a) suggested that, owing to possible variation in water content, dry weight i s best representative of maternal input, Thirdly, and most important, I used wild plankton as the food, I assumed i t would be a more natural food source. It would have a broader size spectrum, which might change the impact of size at hatching. Although smaller medaka could not feed as well on one species of paramecia, there was no reason to assume that they would be less able to feed cn smaller food items. The female smelt I collected were one or two years old and produced two d i s t i n c t size groups of eggs, (Cn an e a r l i e r attempt- at smelt-rearing I observed a s i m i l a r egg size d i s t r i b u t i o n in females from a d i f f e r e n t stock; Khidbey Island, Puget Sound) Schaefer (1934) reported that in Surf Smelt, egg si z e increased d i r e c t l y with length of the female. The data in t h i s sample were too limited to show whether female age or s i z e was the best predictor of egg size. 53 The three measures of egg size were well correlated with one another: a l l the smelt females were presumably ready to spawn. As suggested by Bagenal (1969a) , water content variation may be a problem only in samples from a population of females of varying maturity. Dry egg weight was i n every case better correlated with l a r v a l • measurements at hatching; but the c o r r e l a t i o n c o e f f i c i e n t s corresponding to di f f e r e n t measures of egg size were not s i g n i f i c a n t l y d i f f e r e n t . Size at hatching varied as expected with egg size, Egg weight was correlated with a range i n mean length at hatching of almost 1 mm. The variation i n hatched size suggests that we could see i f the medaka results apply more generally. Unfortunately, there were no differences* s i g n i f i c a n t or otherwise, in l a r v a l size or shape among the starvation, "low," or "high" food treatments. I therefore assumed a l l animals were starved. There should have been enough time for growth differences • to appear, as indivi d u a l s had food items in their i n t e s t i n e s at 4 days of age. Perhaps the explanation for the lack of feeding l i e s i n an inadeguate feed supply. Plankton was collected in late October, at least one month after l o c a l smelt spawning had ceased. No f i s h larvae of any species were observed i n over 40 plankton tows, Many l a r v a l studies have shown that high densities of food are e s s e n t i a l . Others suggest that the actual food item, or the size spectrum may be c r i t i c a l , Although fresh plankton was introduced d a i l y , i t l i v e s a short time only. F i n a l l y , the physical conditions of the rearing chambers may not have been 54 conducive to l a r v a l feeding. length and dry weight of f i s h from the starved chambers were s t i l l well correlated, 11 to 12 days aft e r hatching, with siz e at hatching and egg size. Mouth-width was correlated with length, and varied more dramatically than i n the medaka. when i t appeared that the larvae were not feeding, I used the data to measure survival under starvation. The smelt survived for a longer period than i n two previous attempts (Schaefer, 1934; Yapchionges, 1949). This was probably the r e s u l t of lower temperature, but i t does suggest that the physical conditions were s a t i s f a c t o r y . fi measure of yolk reserve at hatching, calculated as yolk volume over length (yolk/length , where b = 3,0, 3,5, or 4.0), was s i g n i f i c a n t l y and p o s i t i v e l y correlated with the duration of s u r v i v a l (Elaxter and Hempel, 1 963). The correlation between egg dry weight and yolk reserve at hatching might lead one to expect a similar c o r r e l a t i o n of egg dry weight and s u r v i v a l . However, the data were too poor to show any c o r r e l a t i o n , Thus starvation resistance was not correlated with egg size. C. The Interaction Between Egg Size and Egg Number Pianka (1972) suggested that egg number and egg size are two interacting components of an organism's l i f e history strategy. But among f i s h which are broadcast-spawners there seems to be no necessary connection between the amount of energy 5 5 that i s to be devoted to reproduction and the manner i n which that energy i s divided per offspring. As stated by Svardson (1949), offspring size represents a trade-off between the ef f e c t s on i n d i v i d u a l v i a b i l i t y of increased egg s i z e , and the numerical advantage of decreased egg size. Except for the physiological r e s t r a i n t s on increased egg s i z e , v i a b i l i t y must i n -general be p o s i t i v e l y related to size at hatching; otherwise there would be continued selection for those females which produce the most eggs from a given reproductive e f f o r t . Reproductive e f f o r t i s assumed to be a function of adult food conditions and "expectation" of future s u r v i v a l , while e f f o r t per offspring i s assumed to be a function of the incubation and l a r v a l environments. Given t h i s approach, egg s i z e among brcadcast-spawners cannot be expected to be necessarily correlated with other components of a species' l i f e history. The data presented i n t h i s paper i l l u s t r a t e the dynamic nature of the "value" of added size at hatching. The change in v i a b i l i t y with egg s i z e , or size at hatching, w i l l i t s e l f be determined by an environment which changes in time and space. For example, the e f f e c t cn feeding of an absolute difference i n size at hatching w i l l vary with type, abundance, and d i s t r i b u t i o n of the food. The trade-off of guantity versus guality depends on the r e l a t i v e and variable importance of s i z e -s e l e c t i v e mortality and the precision of that s e l e c t i o n . although there i s assumed to be an optimal egg size for a given environment there w i l l s t i l l be v a r i a b i l i t y about that size. Selection w i l l always lag in time, and r e f l e c t genctype 56 selection of the previous year under a variety of conditions. Egg size v a r i a b i l i t y may enhance population s u r v i v a l , i n that a hierarchy of v i a b i l i t y would be created. In the presence of competition, larvae of lower v i a b i l i t y would more rapidly succumb and not reduce the v i a b i l i t y cf a l l larvae. It i s net suggested, however, that this e f f e c t has been a c t i v e l y selected, It remains to be explained why egg size varies systematically with female size or age. Why do small females tend to produce smaller eggs i f selection for egg size i s wholly defined by the incubation and l a r v a l environments? One explanation i s that there may be physiological costs associated with producing eggs of a s p e c i f i c size as ovaries change in s i z e . For example, ovarian vascularization may have to increase at a greater rate than ovarian volume in order to produce more eggs of egual s i z e . Possibly, yolk deposition occurs at a fixed rate and younger or smaller females have less time in which to mature (Hulata, Mcav, and Wohlfarth, 1974), The above explanations suggest that egg size i s selected not only by the incubation and rearing environments after spawning, but by the ovarian conditions during egg maturation, which i n turn must be affected by the maternal environment prior to spawning. Perhaps i t i s incorrect to assume that reproductive e f f o r t and i t s pa r t i t i o n i n g do not i n t e r a c t among those species which are are broadcast-spawners, ft t h i r d explanation i s that since smaller spawners may spawn at s l i g h t l y d i f f e r e n t times (possibly i n response to d i f f e r e n t rates of maturation, Schaefer, 1934; Nikclsky, 1965; Ciechomski, 1966) , egg size may be adapted to s l i g h t differences 57 i n spawning environment, D, Implications for Fishery Management While the medaka results have interesting ramifications, there remains the o r i g i n a l guestion of whether egg size v a r i a t i o n within a stock i s of v a l i d concern to a fishery manager. Would egg size variation explain some of the variance i n stock-recruit studies, as suggested by Schopka and Hempel (1973)? The Surf Smelt presents an i n t e r e s t i n g context for discussion. It has discrete ages of spawners, which produce d i f f e r e n t sized eggs. If a stock i s managed comprehensively, i t s size or age d i s t r i b u t i o n could be manipulated. Would i t be worth a possible reduction i n exploitation to guarantee a spawning nucleus of 2-year-olds? Two-year-old females not only produce three times as many eggs, but have larger eggs. Even i f there i s no stock-recruit relationship ( n u l l i f y i n g the e f f e c t of the increase in fecundity), recruitment may be determined by l a r v a l survival, A spawning nucleus of 2-year-olds would guarantee the production of large larvae, and the recruitment would then be p a r t i a l l y buffered against these years when plankton productivity i s low, The larvae from the one-year-old females might be e s p e c i a l l y vulnerable to poor feeding conditions, It might be assumed, i n marine pelagic stocks, that non-s e l e c t i v e mortality overwhelms the e f f e c t s of g u a l i t a t i v e 58 variations among the larvae. Bat Bridger (Bridger, 1959; and Cushing and Bridger, 1965) has found, in Downs herring, that the younger 3- and 4-year-cld r e c r u i t spawners (which produce smaller eggs) contributed l i t t l e to recruitment, and that larvae produced by these females shewed lower s u r v i v a l . Unfortunately, he rejected his explanation of the variation cf l a r v a l s u r v i v a l i n response to the starvation-resistance experiments of Blaxter and Hempel (1963), Here recently Ponoraarenko (1973) has observed a positive c o r r e l a t i o n between l a r v a l s u r v i v a l and the average age cf the spawners in the Barents Sea cod, whether or net stock abundance i s affected by changes i n egg size depends on the r e l a t i v e importance of the variance i n v i a b i l i t y associated with egg s i z e , versus the variance due to environmental e f f e c t s . If small increases in length at hatching lead inevitably to a greater growth rate, and the larger larvae have access to more food types, then the influence of s i z e at hatching would have profound effects on abundance. Those segments of the population which produce smaller eggs could be visualized as "fringe" producers. During years of high indiscriminate mortality, small egg producers would produce more successful offspring for a given reproductive e f f o r t . Cn the other hand, Hunter (1976) has shown that r a i s i n g anchovy larvae successfully in the laboratory reguires an overlapping sequence cf four food types, P, mu1timicrenucleatum may be best thought of as a second food source for medakas, If the larvae had been fed smaller infuscrians from hatching, then the s p e c i f i c growth rates cf a l l larvae might have been equal to 59 that of the large larvae feeding upon paramecia. I f the impact of size at hatching i s reduced to t h i s l e v e l , the impact on recruitment might be swamped by environmental variation in the physical conditions, absolute food abundance, and, most importantly, patchiness of prey. If larvae reguira large densities of prey, then survival may well depend on whether the larvae find a patch of food. The r e l a t i v e size at which they enter ' the patch would have a more subtle e f f e c t , and not measurably affect abundance. If small-scale patchiness i s c r i t i c a l to survival,and larvae show aggressive behaviour, then i n t r a s p e c i f i c competition may provide the density-dependent factor for which fishery people have been searching (Jones and H a l l , 1974; Cushing, 1974). The observations of Eridger and Ponomarenkc suggest that a reduction in average adult age can ultimately reduce recruitment. But whether t h i s inference i s merely another example cf the danger of time-series correlations (Gulland, 1965), or whether they r e f l e c t a real and widespread phenomenon, i s unknown. Data presented in t h i s paper and others have shewn that decreased egg s i z e , associated with decreased average spawning s i z e , could possibly account for t h i s phenomenon. 60 E. Future Studies 1, Fishery data could be examined for the e f f e c t s cf age d i s t r i b u t i o n on recruitment and l a r v a l s u r v i v a l . While increased reliance on young spawners may not be s i g n i f i c a n t l y correlated with recruitment or even l a r v a l s u r vival (especially i f examined with a univariate design), age d i s t r i b u t i o n may be associated with increased v a r i a b i l i t y of l a r v a l abundance. Studies should examine a number of species to see i f there are patterns among ecological or systematic groupings. 2, Larvae could be studied in the laboratory tc determine the persistence of the advantages of larger size at hatching. The food parameters of type, abundance, and d i s t r i b u t i o n , could be manipulated to see what determines the optimum size at hatching. This would test the hypothesis that larger larvae are better able to exploit poor food conditions. The t r o p i c a l fish-paramecia system would provide an elegant experimental s i t u a t i o n in which to conduct these experiments. Different-sized s t r a i n s of paramecia could be used singly, in combination, and in di f f e r e n t densities - or di s t r i b u t i o n s , within these same experiments, the r e l a t i v e importance of size versus age could also be examined. Age and maturity e f f e c t s have been neglected i n l a r v a l f i s h models. 3, Larvae i n the natural environment could be examined tc see 61 how food composition and feeding success change with different plankton production periods, p a r t i c u l a r l y when the dif f e r e n t periods are associated with d i f f e r e n t spawning groups, and offspring of d i f f e r e n t sizes or species, 4, An examination of the influence of external variables (rate of growth and maturation) may explain why smaller females produce smaller eggs, Bagenal (1969a) and H o r r e l l (1973) claim that offspring size i s inversely correlated with the amount of food given to a maturing female. 62 V, CONCLUSIONS •1. In the medaka, egg size was correlated with length and dry weight at hatching, hut not with the a b i l i t y to withstand starvation, 2. When fed l i v e paramecia for four days, medaka larvae grew faster and were in better condition i n proportion to o r i g i n a l egg s i z e . (This r e l a t i o n was the same at two leve l s of feeding.) 3. when fed a combination of "prepared" food and a protozoan culture of organisms smaller than paramecia, growth and condition were the same regardless of o r i g i n a l egg s i z e . 4. Two-year-old Surf Smelt produced eggs approximately 50$ heavier than those of one-year-olds. There was a corresponding variation in weight, and a range in brood mean length cf almost 1 mm at hatching. 5. Smelt l a r v a l survival during starvation was not correlated with o r i g i n a l egg s i z e , but i t was correlated with the ra t i o of yolk volume to body size at hatching. 6. It has been assumed that large size at hatching increases an i n d i v i d u a l offpsring's chance of s u r v i v a l . Therefore, selection for egg s i z e , within physiological r e s t r a i n t s , must represent a tradeoff of quality versus quantity. Data 6 3 p r e s e n t e d i n t h i s p a p e r show t h a t t h e " q u a l i t y " a s p e c t o f s i z e a t h a t c h i n g i s a dynamic v a r i a b l e , and c h a n g e s w i t h s p e c i f i c f e e d i n g c o n d i t i o n s a t t h e t i m e o f y o l k r e s o r p t i o n . 7. l a r g e r f i s h t e n d t o p r o d u c e l a r g e r e g g s . w h i l e i t i s e x p e c t e d t h a t l a r g e r f e m a l e s have more t o i n v e s t i n r e p r o d u c t i o n , i t i s u n c l e a r why t h e d i v i s i o n o f r e p r o d u c t i v e e f f o r t s h o u l d be s i z e - d e p e n d e n t . I f egg s i z e v a r i e s s y s t e m a t i c a l l y a c r o s s age o r s i z e g r o u p s t h e n e i t h e r t h e g r o u p s a r e r e s p o n d i n g t o s l i g h t l y d i f f e r e n t spawning e n v i r o n m e n t s o r t h e p h y s i o l o g i c a l c o s t o f p r o d u c i n g eggs o f a g i v e n s i z e v a r i e s w i t h body s i z e . 8. I f t o o s m a l l f o r t h e k i n d s c f f o o d a v a i l a b l e , h a t c h l i n g s w i l l grow p o o r l y and p r o b a b l y s u r v i v e p o o r l y t o o . E x p e r i m e n t s t h a t t a k e no a c c o u n t o f t h i s s i z e r e l a t i o n a r e s u s p e c t . A l s o , v a r i a t i o n i n s i z e o f egg (and t h u s i n s i z e o f h a t c h i n g ) may be one more v a r i a b l e a f f e c t i n g abundance c f f i s h e r y s t o c k s . 64 LITERATURE CITED Anokhina, A. .H* 1S68. On the quality of eggs of the Shite Sea navaga i n r e l a t i o n to the abundance cf offspring* Vop. I k h t i o l , , 8: 1004-1008, Arthur, David K, ' 1976. Food and feeding of larvae of three fishes occurring i n the C a l i f o r n i a Current, Sardiriops s ag a x, Enqraulis mordax and Trachurus symmetricus, Fish. B u l l . 74: 517-530, Bagenal, T. B. 1969a, The r e l a t i o n s h i p between food supply and fecundity in brown trout Salmo t r u t t a I. J, Fish. B i o l , 1: 167-182. 1969b, Relationship between egg s i z e and fry survival i n brown trout Saline trutta 1. J. Fish E i o l , 1: 349-355. 1971. The i n t e r r e l a t i o n of the size of f i s h eggs, the date of spawning and the production cycle, J. Fish E i o l . 3: 207-219. 1973. Fish fecundity and i t s r e l a t i o n with stock and recruitment, Rapp. P.-v. Cons. Reun, Explor, Her. 164: 186-198. Beverton, R. J, H, 1962, Long-term dynamics of certain North Sea f i s h populations. Pages 242-264 in E. D. LeCren and M. W. Holdgate (eds,). The exploitation of natural animal populations, Blackwell, London, B i l t o n , H. T, 1970, The maternal influence on the age at maturity of Sk'eena River Sockeye Salmon (Oncorhinchus nerka). Fish, Res. Board Can. Tech, Rept. 167. 20p, 65 B l a x t e r , J, H. S. 1969, Development: Eggs and Larvae. Pages 178-252. i n «. S, Hoar and D. J. B a n d a l l (eds,). F i s h Physiology, V ol. 3. Academic Press, New York, B l a x t e r , J, H. 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Havunders, 15: 368-37S. 1974, The p o s s i b l e density-dependence of l a r v a l m o r t a l i t y and a d u l t m o r t a l i t y i n f i s h e s . Pages 103-112. i n J. H, S, B l a x t e r (ed,). E a r l y L i f e H i s t o r y of F i s h . S p r i n g e r - V e r l a g , Heidelberg. Cushing, D, H, and J , P. B r i d g e r . 1966, The stock of h e r r i n g i n the North Sea and changes due to f i s h i n g . 0, K. Min, A g r i c , F i s h . I n v e s t . , Ser. 2, v o l . 25. no. 1. 123p, 66 Dahl, K. 1918, Studies of trout and trout waters, in Norway. Salm, Trout. Mag, 17: 58-79. Day, Frances, 1687. B r i t i s h and I r i s h Salmonidae. Williams and Norgate, London, p. 298. Gray, J, 1926. The growth of f i s h : I. The r e l a t i o n s h i p between embryo and yolk in Salmo f a r i o . B r i t . J. Exp. B i c l - 4: 215-225, . Gulland, J. 1965, Survival of the youngest stages of f i s h , and i t s r e l a t i o n to year class strength. Int. Comm, N. W. A t l a n t i c . Fishery Environmental Symposium, Spec. Pub, 6: 363-371. 1973, Can a study cf stock and recruitment aid management decisions? Rapp. P.-v, Cons. Reun. Explcr. Her. 164: 368-372, Hempel, G 1965, On the importance of l a r v a l s u r v i v a l for the population dynamics of marine food f i s h , C a l i f . Coop, Oceanic Fish, Invest. Rept, 10: 13-23. Hjort, J. 1914. Fluctuations in the great f i s h e r i e s of northern Europe viewed in the l i g h t of b i o l o g i c a l research. Rapp, P,-v» Cons, Reun. Explcr. Her. 20: 1-228, Hulata, G,,R, Moav, and G. Wohlfarth, 1974. The relationship of gonad size and egg size tc weight and age in the European . and Chinese races of the commom carp C^jprinus carjgio L. J. Fish, B i o l , 6: 745-758, 1976, The e f f e c t s of maternal s i z e , r e l a t i v e hatching time and density of stock on growth rate of fry in the European and Chinese races of the common carp. J. 67 Fish Bic-l. 9: 499-513. Hunter, John R. 1972. Swimming and feeding behaviour of l a r v a l anchovy Engraulis mordax. Fish. B u l l . 70: 821-838. 1976. Culture and grosth of northern anchovy, Engraulis mordax, larvae. Fish. B u l l . 74: 81-88. ~~ ~ ' ~* Ivlev, 1965, On the guantitative relationship between survival rate of larvae and the i r food supply. B u l l , Math. Biophys, 27: 2 15-222. and i . B. Hall , Some observations on the population dynamics cf the l a r v a l stage in the common gadoids. Pages 87-102 i n J. H» S. Blaxter (ed.). Early l i f e History of Fish. Springer-Verlag, Heidelberg, Kerfoot, W. Charles. 1974. Egg cycle of a cladoceran. Ecology 55: 1259-1270. Kirpichnikov,V. S. 1966. Methods of progeny testing spawners on carp f i s h farms. Pages 36-55. i n , V, S. Kirpichnikov (ed.). Selective breeding of carp and i n t e n s i f i c a t i o n of f i s h breeding in ponds. E u l l . State Sci, Res, Inst. Lake and River Fishes. Vol. 61, (Transl, from Russian) I s r a e l Program for S c i e n t i f i c Translations. Jerusalem,1970. Jones, R. 1974, Lack, D. 1947, The sign i f i c a n c e of clutch size. Ibis 89: 302-352. Lenarz, William H, and John Hunter. A discussion on the adaptive values cf variation of f i s h egg size. (manuscript, Southwest Fisheries Center, La J o l l a , 0. S. A. ,CA 92038). 68 M a r s h a l l , N. E. 1953, Egg s i z e i n a r c t i c , a n t a r c t i c and d e e p - s e a f i s h e s , E v o l u t i o n 7: 328-341, May, R o b e r t C, 1970. F e e d i n g l a r v a l m a r ine f i s h i n t h e l a b o r a t o r y : a r e v i e w . C a l i f . Coop. O c e a n i c F i s h . I n v e s t . Rept. 14: 76-83, M e n d i o l a , E. R. de, 1974. Food o f t h e l a r v a l a n c h o v e t a E n g r a y l i s r i n g e n s . Pages 277-286 i n J. H. S, B l a x t e r ( e d . ) . E a r l y L i f e H i s t o r y o f F i s h . S p r i n g e r - V e r l a g , H e i d e l b e r g . 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