EHRLICH ET AL: THERMAL BEHAVIORAL RESPONSES OF FISHES 



fish with wide temperature tolerances from a par- 

 ticular area until stress-inducing conditions are 

 reached. 



Temperatures Selected and 

 Their Relationship to Thermal History 



We classified the behavioral responses of the 16 

 species surveyed into four groups based on 

 changes in temperatures selected throughout an 

 experiment: 1) immediate response — no general 

 shift in selected temperature over time, 2) fast 

 response — a shift in selected temperature not ex- 

 ceeding the first 2 h of the run, 3 ) slow response — a 

 shift in selected temperature over more than 2 h, 

 and 4) positioned response — a broad preference 

 and a tendency to remain in a given position in the 

 gradient until conditions become extreme. 



Shiner surfperch, Cymatogaster aggregata; pile 

 surfperch, Damalichthys vacca; black surfperch, 

 Embiotoca jacksoni; and black croaker, Cheilo- 

 trema saturnum, showed the first behavioral pat- 

 tern of immediate response (Figure 4). These 

 fishes moved most quickly from their preexperi- 

 mental acclimation temperature to their final 

 selected one or range, remaining there for the du- 

 ration of the experiment. These fishes generally 

 had the narrowest selected temperature ranges 

 and also aggregated tightly (Table 1). 



Fishes with a fast response to the temperature 

 gi'adients included speckled sanddab, Citharich- 

 thys stigmaeus; seiiorita, Oxyjulis californica; 

 spotted sand bass, Paralabrax maculatofasciatus; 



25 

 20 



— 15 



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 o 



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Cymatogaster aggregota 



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Damalichthys vocco 



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Embiotoca jacksoni 



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Cheilotrema saturnum 



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Figure 4. — Immediate response to temperature change. These 

 species showed no trend in selected temperature with time. Dots 

 are mean selected temperatures and vertical lines are 1 SD about 

 the means. Results are for duration of one experiment. 



and sculpin Scorpaena guttata (Figure 5). These 

 species required up to 2 h to home in on a selected 

 temperature and also generally did not aggregate 

 as tightly, nor select as narrow a temperature 

 range as those fishes that showed an immediate 

 response to the temperature gradients (Table 1). 

 All larvae studied responded slowly under ex- 

 perimental conditions. These included topsmelt, 

 Atherinops affinis; California grunion, Leuresthes 

 tenuis; rockpool blenny, Hypsoblennius gilberti; 

 and painted greenling, Oxylebius pictus (Figure 

 6). Four older fishes also showed this behavior: 

 kelp bass, Paralabrax clathratus; olive rockfish, 

 Sebastes serranoides; California halibut. Para- 



TABLE 1. — Behavioral responses of larval and juvenile fishes in temperature selection experiments. Initial and final selected 



temperatures are taken from Figures 4-6 and other similar experimental data. 



•P<0.05. 



843 



