Buckley et al Effects of water temperature on Pseudopleuronectes amencanus 



425 



content was lowest at the intermediate incubation tem- 

 perature (7°C). DNA content at first feeding showed 

 no significant temperature interaction and was unaf- 

 fected by either spawning or incubation temperature. 

 Protein content at first feeding showed a significant 

 temperature interaction. At both spawning tempera- 

 tures, protein content decreased with increasing in- 

 cubation temperature. 



Discussion 



Winter flounder spawn and embryos survive over a 

 wide range of temperatures. In the laboratory, Wil- 

 liams (1975) observed survival of embryos between 

 - 1.8° and 15°C. Rogers (1976) reported survival be- 

 tween 3° and 14°C. While 2°C is close to the temper- 

 ature of maximum egg production, winter flounder 

 larvae require water temperatures above 2°C for sur- 

 vival to metamorphosis (Laurence 1975, Buckley et al. 

 1982). Spawned through the late winter and early 

 spring, winter flounder embryos and larvae generally 

 experience gradually increasing water temperatures. 

 In shallow estuaries and bays, however, embryos and 

 larvae may be subjected to large fluctuations in salin- 

 ity and water temperature over relatively short periods 

 of time, or to prolonged periods of abnormal warming 

 or cooling. The effects of such changes in water tem- 

 perature on survival and growth of the early-life stages 

 of winter flounder are largely unknown. 



Inverse relations between water temperature (dur- 

 ing late winter and early spring) and indices of recruit- 

 ment have been reported for winter flounder (Jeffries 

 and Johnson 1974, Jeffries and Terceiro 1985, North- 

 east Utilities 1988). The shape of larval abundance 

 curves, a parameter affected by water temperature, 

 has also been related to recruitment; cold years with 

 broad shallow abundance curves produce good year- 

 classes (Northeast Utilities 1988). 



The size and chemical composition of larvae at initia- 

 tion of feeding provide useful criteria for evaluation 

 of these temperature effects, and may provide insight 

 into causal mechanisms. Feeding initiation is the end 

 point of the period of reliance on endogenous energy 

 reserves that commences at ovulation. Increased lar- 

 val size confers increased potential for survival, since 

 larger larvae are better able to avoid size-dependent 

 predation, capture food, and survive periods of star- 

 vation (Blaxter and Hempel 1966, Rosenberg and 

 Haugen 1982, Bailey and Battey 1984, Knutsen and 

 Tilseth 1985). DNA content is an index of cell number 

 and RNA content an index of the capacity for protein 

 synthesis and hence growth (Bulow 1987). Buckley 

 et al. (In prep.) demonstrated direct relations between 

 size and RNA content of yolksac winter flounder larvae 



and survival for the first month of life in the laboratory. 

 Size of larvae at first feeding is dependent upon egg 

 size at spawning and the efficiency of production of lar- 

 val tissue (yolk-conversion efficiency). 



Based on observations of the timing of yolk absorb- 

 tion and first feeding, and the size and composition of 

 winter larvae produced by a single female spawned at 

 2°C, Buckley (1982) speculated that eggs spawned at 

 low temperatures (2°) may be poorly suited for growth 

 and survival at high temperatures (10°C) within the 

 range of tolerance of winter flounder. The present fac- 

 torial study of six females spawned at low (2°C) and 

 high (7°C) temperatures confirmed and extended these 

 earlier findings. However, unlike the earlier study, first 

 feeding occurred within one day of completion of yolk 

 absorbtion at all combinations of adult acclimation 

 (prespawning) and incubation temperature (Table 2). 

 The present study, with the spawn from six winter 

 flounders, demonstrated the importance of variability 

 at the level of individual females in determining size 

 and composition of winter flounder larvae (Tables 3 and 

 4). Adult acclimation (prespawning) temperature was 

 important alone or in combination with embryo incuba- 

 tion temperature in determining length and RNA and 

 DNA content at hatch, and in determining length and 

 RNA and protein content at first feeding (Table 5). Em- 

 bryo incubation temperature was important alone or 

 in combination with adult acclimation temperature in 

 determining larval size, yolksac volume, RNA and DNA 

 content at hatch, and in determining length and RNA 

 and protein content at first feeding. At first feeding, 

 size and chemical content of eggs spawned by adults 

 acclimated to 2°C were maximized at the lowest in- 

 cubation temperature (4°C). Eggs spawned at 7°C pro- 

 duced the longest first-feeding larvae at 4°C, while 

 DNA and protein content were highest at the inter- 

 mediate incubation temperature (7°C) and RNA con- 

 tent was highest at the warmest incubation tempera- 

 ture (10°C). The largest larvae, whether measured by 

 length or chemical content, were produced at the low- 

 est combination of acclimation and rearing tempera- 

 tures. RNA content, which is critical to protein syn- 

 thesis and growth, was highest at fn-st feeding in larvae 

 incubated at 4°C for eggs produced at 2°C, and at 10°C 

 for eggs produced at 7°C. RNA content was lowest in 

 first-feeding larvae produced from eggs spawned at 

 2°C and incubated at 10°C. This group represented the 

 largest difference between spawning and incubation 

 temperature. 



Hempel and Blaxter (1967) reported differences in 

 fecundity and egg size between Atlantic herring stocks 

 spawning at different temperatures. Stocks spawning 

 at colder temperatures produced fewer but larger eggs. 

 Tanasichuk and Ware (1987) working with Pacific her- 

 ring found that both size-specific fecundity and egg 



