420 



Fishery Bulletin 88(3), 1990 



has been related to swimming speed and the abihty to 

 capture prey and avoid preditors (Folkvord and Hunter 

 1986, Miller et al. 1988). Bulk RNA content is primarily 

 a measure of ribosomal RNA content which is an in- 

 dex of an organism's capacity for synthesis of protein 

 and growth (Bulow 1987). DNA content is an index of 

 cell number and developmental state. Protein, the 

 primary organic constituent in fish larvae, is general- 

 ly proportional to dry weight (Buckley 1979). Growth 

 of fish larvae is primarily accomplished through pro- 

 tein synthesis and accumulation. Protein is also an im- 

 portant source of reserve energy during larval develop- 

 ment (Buckley 1979). 



The primary hypothesis tested was that water tem- 

 peratures, both during gamete maturation and during 

 embryonic and early larval development, and their in- 

 teraction had an effect on the size and composition of 

 larvae produced. It was reasoned that eggs produced 

 by adults acclimated to low temperatures would be 

 better adapted to low temperatures than eggs produced 

 by adults acclimated to high temperatures. It was ex- 

 pected that the converse was true for eggs produced 

 by adults acclimated to high temperatures. This study 

 originated in part out of an earlier study indicating that 

 winter flounder embryos produced at low temperature 

 exhausted their yolk reserves prior to feeding initia- 

 tion and appeared poorly suited for growth and sur- 

 vival when incubated and reared at higher tempera- 

 tures (Buckley 1982). It is part of a larger study of the 

 effects of parental and environmental factors on the 

 size and viability of winter flounder eggs and larvae. 

 The rationale for this larger effort is that given the high 

 fecundity of temperate marine fishes and the high mor- 

 tality rates during their early life stages, variability at 

 the individual, brood and stock level in size and com- 

 position of fish eggs and larvae may play a large part 

 in determining survival during the early life stages and 

 consequently in determining recruitment success. 



Methods 



Table I 



Experimental design. Three Pseudopleuronectes americanvs 

 females were spawned at each of two acclimation tempera- 

 tures (2°. 7°C). Subsamples of about 1500 eggs from each 

 female were incubated in separate containers at each of three 

 temperatures (4°, 7°, 10°C). Triplicate samples of 40 larvae 

 each were taken from each tank for biochemical analysis. 



Stage 



Temperature 



Time 



Adults 



Capture 



3.5°C 



/ \ 



Acclimation 



2°C 7°C 48-51 days 



i i 



Incubation 



Embryos-Larvae 4, 7, ICC 4,7,10°C 13-29 days 



Adults-Garnets 



incubated at 4°, 7°, and 10°C in 38-L black glass 

 aquaria. Eggs and larvae were not incubated at 2°C 

 because of the high mortality observed at this temper- 

 ature in earlier studies (Laurence 1975, Buckley 1982). 

 Embryos were gradually acclimated to the incubation 

 temperatures at the rate of 1°C per 6 hours. After 

 hatching, larvae were fed live zooplankton collected in 

 the Narragansett Bay area and sieved to select the ap- 

 propriate size fraction. Plankton densities were main- 

 tained at greater than 2 plankters per mL. 



Groups of 10 larvae were examined daily, between 

 0800 and 1100 hours, under a dissecting microscope 

 to establish the day of completion of yolksac absorp- 

 tion and first feeding. Larvae were judged to have com- 

 pleted yolksac absorption when 5 out of 10 larvae had 

 no visible yolk. Larvae were judged to have initiated 

 feeding when 5 out of 10 larvae examined had food visi- 

 ble in their gut. At hatching and first feeding 10 lar- 

 vae from each group (one unique combination of accli- 

 mation and incubation temperatures for each female) 

 were measured for standard length with a filar microm- 

 eter in a dissecting microscope. Yolk volume was esti- 

 mated using the equation for a prolate spheroid: 



Mature winter flounder were caught with an otter 

 trawl on 23 December 1980 in the West Passage of 

 Narragansett Bay in the vicinity of Fox Island at a 

 water temperature of 3.5°C (Table 1). Fish were ran- 

 domly assigned to two groups (acclimation tempera- 

 tures). One was held at 2°C, the other at 7°C. Spawn- 

 ing was induced by injections of carp pituitary extract 

 administered as described by Smigielski (1975). Eggs 

 were stripped, fertilized with the sperm of three males 

 held at the same temperature as the spawning female, 

 and treated with diatomaceous earth (Smigielski and 

 Arnold 1972). Embryos from each female were ran- 

 domly split into three groups of about 1500 each and 



V = (n/6) LH'^ 



where L is the length and H is the height of the yolksac 

 (Laurence 1973). Triplicate groups of 40 larvae each 

 were sampled at the same times for biochemical anal- 

 ysis. Larvae were homogenized in 2.0 mL of ice-cold 

 distilled water using an all-glass tissue grinder. Sub- 

 samples of 1.4 and 0.1 mL of homogenate were used 

 for analysis of nucleic acids and protein, respectively, 

 as outlined in Buckley (1979). Nucleic acids were deter- 

 mined using a modification of the Schmidt-Thannhau- 

 ser method. A modification of the Lowry method was 

 used for determination of protein. Coefficients of varia- 



