Gadomski and Caddell: Temperature effects on Parahchthys californicus 



57! 



Table 3 



Mean standard lengths of 97-day-old juvenile California hali- 

 but Paralichthys californicus at four temperature treatments 

 (acclimated when 1 month old from 16.7°C). Three replicates 

 were maintained at each temperature, with initially 25 larvae 

 per replicate. N = combined number of surviving juveniles 

 in the three replicates. 



Standard length (mm) 



Mean 



SE 



18.48 (0.93) 



18.10 (0.39) 



24.24 (0.57) 



26.92 (0.71) 



icantly from 20°C (P<0.05), but final mean length was 

 significantly larger at 24°C, and larger at 28°C than 

 24°C (Table 3). These results were unexpected, since 

 all previous experiments have demonstrated greater 

 growth at 20°C than 16°C (Gadomski et al. 1990). 

 Measurements of dead fish removed during the last 15 

 days of the experiment, however, indicated that smaller 

 individuals were dying at 16°C than at 20°C, which 

 biased the final growth data. Mean standard lengths 

 at 16°C of fish that died during two time periods— the 

 five (days 63-67) and fifteen (days 53-67) day inter- 

 vals before the end of the experiment— were similar, 

 12.68 mm (SE 0.77, n 8) and 12.57 mm (SE 0.49, n 14), 

 respectively, and were significantly smaller (P<0.01) 

 than mean mortality lengths at 20 °C for these same 

 two time periods, 17.46mm (SE 2.02, n 3) and 16.21 

 mm (SE 1.12, n 8). The mean standard length (12.68 

 mm, SE 0.77, n 8) of fish that died near the end of the 

 experiment (days 63-67) at 16°C was also significant- 

 ly smaller (P<0.05) than the final mean standard length 

 of surviving individuals at 16°C, 18.48mm (SE 0.93, 

 n 23), indicating that size-selective mortality had 

 occurred. 



Larval settlement 



There were no significant differences in survival be- 

 tween temperatures (P<0.01), with individual tank sur- 

 vival ranging from 80% to 93%. Larvae settled sooner 

 at 20°C (actual mean temperature 20.0 C C, SE 0.0) than 

 16°C (15.8°C, SE 0.1) (Fig. 3). At 20°C, 50% had 

 settled by 6-8 days after transfer from 16°C, and all 

 were settled by 10 days after transfer (when 40 days 

 old). In contrast, at 16°C, 50% settlement did not occur 

 until 12-15 days after transfer, and the last few larvae 

 did not settle until 21-22 days (when 51-52 days old). 

 At the end of the experiment, larvae held at 20 C C 

 were significantly larger (P<0.01) than those at 16°C. 



< 



> 60 

 > 



cc 



=> 

 CO 1° 



20° C 

 ~28°C 



• 24° C 



16°C 



DAY (initial age = 30 d) 



Figure 2 



Survival (%) over a 67-day period of California halibut Para- 

 lichthys californicus larvae and juveniles at four temperatures. 

 Larvae held at 16.7°C were transferred into experimental 

 containers when 30 days old. Points are replicates (n 3) 

 combined. Each replicate initially consisted of 25 larvae. 



D 



w 60 



t= 



LU 



CO jo 



• — » B iL 



DAY (initial age = 30 d) 



Figure 3 



Percent of California halibut Paralichthys californicus settled 

 per day at 16°C and 20°C. Larvae held at 16°C were trans- 

 ferred into experimental containers when 30 days old. Three 

 replicate trials were conducted at each temperature. Each 

 replicate initially consisted of 15 larvae. 



At the beginning of the experiment (when transferred 

 from 16°C), 30-day-old larvae had a mean length of 

 6.74mm (SE 0.10, n 15) with 80% still exhibiting in- 

 complete notochord flexion [the remaining 20% had 

 achieved full flexion (standard length)]. All exhibited 

 full elongation of the second to sixth dorsal rays 



