Gadomski and Caddell: Temperature effects on Paralichthys califomicus 



569 



their similarity, survival curves of 12°C starved and 

 12°C fed trials were additionally compared. 



For the fed trials, analysis of variance (ANO VA) was 

 used to test for significant differences in final survival 

 [ln(number alive+1)] and also differences in mean 

 larval length between temperatures; if significant 

 differences were found, Duncan's multiple range test 

 was applied. 



Juvenile growth and survival 



Twenty-five 30-day-old pelagic larvae, which had been 

 held at a mean ambient temperature of 16.7°C (SE 0.1), 

 were stocked in each of twelve indoor 15 L black fiber- 

 glass tanks (40cm diam., 12cm depth) at 16°C. Water 

 quality was maintained using a slow-drip flow-through 

 system and tank aeration; ammonia and salinity levels 

 were monitored weekly. A natural cycle of light and 

 dark (12L:12D) was provided. Temperatures were 

 raised using aquarium heaters in nine tanks 0.5°C per 

 day from 16°C to 20, 24, and 28°C, resulting in three 

 replicates per temperature. Fish were fed rotifers and 

 newly-hatched brine shrimp nauplii (Artemia sp.) to 

 excess. Dead fish were removed and counted daily 

 and, in the last 15 days of the experiment, measured 

 if not badly decomposed. The experiment was term- 

 inated when fish were 97 days old; survivors were 

 counted and standard lengths determined. ANOVA 

 and Duncan's multiple range test were utilized to test 

 for significant differences in final survival and size 

 between temperatures. Student's i-test was used to 

 test for significant differences in mean standard 

 lengths between 16°C and 20°C mortality and survivor 

 groups. 



three tanks at 16°C. Light cycles simulated natural 

 conditions (12L:12D). Tanks were aerated to maintain 

 water quality and avoid the formation of temperature 

 gradients. Three times a week, 20% of the volume of 

 water in each tank was replaced with fresh seawater; 

 at this time, salinity and ammonia levels were moni- 

 tored. Larvae were fed rotifers and newly-hatched 

 brine shrimp to excess. Dead larvae were removed and 

 counted daily. Each tank was observed for 10 minutes 

 twice daily (morning and afternoon) and the numbers 

 of settled and pelagic larvae counted; the mean values 

 of these two daily observations were used to calculate 

 percent settled larvae per tank per day. We defined 

 "settled" larvae to be individuals that remained on the 

 tank bottom (on their side) for at least 5 seconds dur- 

 ing an observation period. This behavior occurs before 

 metamorphosis is complete (Gadomski et al. 1990). 

 When 100% settlement was observed in all tanks, fish 

 were removed and standard lengths determined. 

 Student's (-test was utilized to test for a significant 

 difference in mean fish lengths between temperature 

 treatments. 



Results 



Egg development 



Halibut eggs are buoyant and about 0.8 mm in diameter 

 with a single 0.14 mm oil globule. Eggs developed to 

 hatching at 12, 16, and 20°C (Table 1). At 8°C, eggs 

 did not develop beyond the 32-cell stage, and at 24°C 

 cell divisions were abnormal and ceased during early 

 development. Time to hatching was inversely propor- 



Larval settlement 



The settlement rate of a group of lar- 

 vae held constantly at 16°C was com- 

 pared with that of a group of larvae 

 from the same cohort exposed to 20°C 

 when a month old. These two temper- 

 ature regimes were designed to simu- 

 late temperatures halibut larvae would 

 encounter in the field if they (1) re- 

 mained in colder offshore waters, or 

 (2) were transported to warmer in- 

 shore areas when a month old. 



Fifteen 30-day-old pelagic larvae 

 that had been held at a mean temper- 

 ature of 15.9°C (SE 0.1) were trans- 

 ferred to each of six indoor 15 L black 

 fiberglass tanks at 16 °C. Tempera- 

 tures were raised 2°C a day to 20 °C 

 in three of the tanks while keeping 



Table 1 



Egg development rates of California halibut Paralichthys califomicus at five 

 temperatures. Times (hours) after fertilization at which developmental events 

 (I-VII) were first observed are presented. Two replicate jars were maintained 

 at each temperature, with initially 300 recently-fertilized eggs per replicate; every 

 2 hours until hatching, at least five live eggs were sampled from each jar and egg 

 development noted. 



Hours post-fertilization 



Mean temp. (°C): 

 SE (°C): 



8.4 

 (0.2) 



12.4 

 (0.1) 



16.0 

 (0.1) 



20.8 

 (0.1) 



23.9 

 (0.6) 



I 2-128 cells 



II Multicelled blastodermal cap 



III Germ ring >l/2 down yolk mass 



IV Embryo visible 



V Blastopore closed 



VI Tail separated from yolk mass 



VII Eggs hatched 



4 

 Dead 



4 

 10 

 26 

 32 

 34 

 52 

 74 



18 

 22 

 24 

 38 

 50 



2 

 6 

 14 

 16 

 18 

 26 

 34 



2 



6 



Dead 



