ROGERS: EFFECTS OF TEMPERATURE AND SALINITY ON WINTER FLOUNDER 



was checked with a refractometer to within 

 ±0.15% of the test salinity. The test salinities 

 were cooled to the ambient seawater temperature 

 (3°C) at which the eggs were incubated for the 

 first 24 h. 



Eggs in lots of 50 were counted into 100-ml 

 polyethylene beakers filled with the test 

 salinities. The beakers were covered with fitted 

 50-mm plastic disposable culture dish bottoms to 

 eliminate evaporation and placed in thermostati- 

 cally controlled water baths at the experimental 

 temperatures. Dead eggs or larvae were removed 

 daily and examined for stage of development. 



Daily observations were made on the develop- 

 ment of embryos. The time of hatching and the 

 duration of the hatching interval were noted so 

 that mean hatching time (time from fertilization 

 to 50% hatch) could be calculated. Abnormal lar- 

 vae (those with curvature of the spine, abnormal 

 yolk sacs, or enlarged fin folds) were noted and 

 counted as nonviable since their chance of con- 

 tinued survival was considered to be small. Pre- 

 maturely hatched or aborted larvae were also 

 considered nonviable in calculations. Such larvae 

 were easily recognized since they were short, 

 thickened, often curled, and in no way resembled 

 a normal healthy larva. 



Each experiment was terminated when all eggs 

 had either hatched or died, and when the larvae 

 could be judged normal or abnormal. From this 

 information, total percentage hatch (percentages 

 of eggs producing live larvae) as well as percen- 

 tage viable hatch (percentage producing viable or 

 normal larvae) was calculated. Salinities were 

 checked at the end of each experiment. 



The experiment was set up as a factorial de- 

 sign. However, replications at different factor 

 combinations were unequal and there were mis- 

 sing data at 3°C due to equipment malfunction. 

 In view of this, a mean value of the replicates was 

 computed for each factor combination and values 

 for the missing data at 3°C were predicted from 

 the hyperbolic equation describing the actual 

 data at 3°C. The resultant design was a 2 factor, 6 

 X 12 (6 levels of temperature and 12 levels of 

 salinity) factorial design with no replicates. Dun- 

 can's multiple range test (Steel and Torrie 1960) 

 was used to compare the mean survivals for each 

 temperature and salinity condition. 



RESULTS 



The results of these experiments indicate that 



winter flounder embryos are euryhaline, with 

 best survival occurring between 10 and 30% but 

 with some survival from 5 to 40%. Hatching oc- 

 curred at all temperatures tested, but the lower 

 temperatures produced the highest survival. In- 

 cubation time and hatching interval were de- 

 creased by increased temperatures and higher 

 salinities. Abnormal development occurred par- 

 ticularly at extremes of salinity but was also 

 influenced by temperature. 



Effects of Salinity and Temperature 

 on Viable Hatch 



Results of the temperature-salinity experi- 

 ments (Table 1) indicated an optimal salinity 

 range between 15 and 25% for temperatures 

 above 3°C and between 15 and 35% for 3°C (Fig- 

 ure 1, Table 2). Viable hatch was highest at 3°C 

 and lowest at 14°C with similar survival rates at 

 5, 7, and 12°C for all salinities. Percentage survi- 

 val at 10°C follows a similar curve at salinities of 

 25% and above, but was between 15 and 30% 

 lower than that of other temperatures at 20% and 

 below. At 3°C, high survival (>78%) occurred 

 from 15 to 35%>, but survival decreased sharply at 

 all other temperatures for salinities above 25%. 



Table l. — Number of winter flounder eggs at each of 67 

 temperature-salinity combinations. Number of replicates 

 shown in parentheses 



Influence of Temperature and Salinity 

 on Total and Viable Hatch 



The influence of temperature and salinity is 

 shown in the percentages of mean total hatch and 

 mean viable hatch (Table 3). There is a sharp de- 

 crease in mean total hatch and mean viable hatch 

 at temperatures over 3°C, while these means ap- 

 proximate a normal distribution at the salinities 

 tested. The mean percentage of abnormal larvae 

 calculated from total and viable hatch data shows 



53 



