15 



10' 



\\ 



Cithorichthys stiqmaeus 



1 1 " ■' I M I H i f * * M *  M H H I 



5*11 



20i 



I I I — I I I I I I • — r- 



3 



• ihl. 



O 10 I 



• •  4 • 



f  



I I I I I I I I I I 



Oxyjulis colifornica 



T 



T 



T 



tt: 15 



UJ 35 



a. 



2 30 



UJ 



t-25 



20 



15 



HI 



W 



lii^ 



Porolabrox maculatofasciotus 



I I I I I I I I 



T 



T 



T 



Scorpoena guttata 



l|tiMlf|||) 



10 ' I I I I I I I I I I I I I I I I 1 I I — I I • « I I • • I 



60 120 180 240 300 360 420 



TIME (minutes) 



Figure 5. — Fast response to temperature change. These species 

 changed their selected temperatures over the first 2 h of the 

 experiment only- Symbols as in Figure 4. 



lichthys californicus; and C-0 turhot, Pleuronich- 

 thys coenosus (Figure 6). Members of this group 

 required more time to stabilize their response 

 than either the immediate or fast responders. The 

 temperature selection acuity and aggregating 

 tendencies of these fishes were similar to those of 

 the second group (Table 1). 



Juvenile topsmelt were the only species ob- 

 served that showed a positioned response (Figure 

 3). Ehrlich et al. (in press) discussed this behavior 

 in detail. California grunion are closely related to 

 topsmelt, and we have observed them together, in 

 the field, throughout larval, juvenile, and adult 

 stages. Possibly juvenile California grunion, 

 which were not tested, may show similar re- 

 sponses. 



Preexperimental acclimation temperatures 

 showed the greatest effect on thermal selection of 

 the fishes during the first 2 h after establishment 

 of the gradient ( Figures 4-6). The short duration of 

 the influence of thermal history on temperature 

 selection has also been reported by Doudoroff 

 (1938). Clearly, trying to determine a preferred 

 temperature for these species or others with simi- 

 lar responses, during the transition period, would 

 make data interpretation difficult. After this ini- 

 tial period, the fishes, in most cases, chose a final 

 selected temperature, which may be synonymous 

 with what Fry (1947) termed the "final preferen- 

 dum." He defined this as the temperature range 



30 



25- 



20 • 

 35 1 



30 



25 



20 



FISHERY BULLETIN: VOL. 76, NO. 4 

 Atherinops offinis larvae 



.. 1^ M p* t f I M JM* *H 



15 

 25' 



20 



O 30' 

 o 



""' 25 



LU 



(T 20 



Z) 



I 



Hilt 



(■■It'ltMil 



Leurestl\as tenuis larvae 



' ' ' I 



.,|nHtt).|||t-*t*'t't' 



Hypsoblennius gilbert i larvae 



T 



T 



T 



.1 



tllH 



ttt)tHtlM(tt*l 



Oxylebius pictus larvae 



< 20-j 

 UJ 15- 



a. 



Ill iiiiiii| 



I • ' ' I 



M|,j|MtH|llt(.Mli.n*' 



Poralabrax ctothrotus 



20' 



15  



10' 

 35' 



30' 



25' 



20' 



15' 



I I I i I I I I I I I I I I I I I I I — I I I I 



 . • 



  ^ M •  



Sebastes serranoides 



-r-^ 



\.^ 



Paralichttiys californicus 



n ,1 4 t " 



10* I I I I I I I I I I I I I I I I — I I I I  — I — I I I I I 



10 



Pleuronictithys coenosus 



*''l]IlT'*»»**+***»»***»* 



1 I I I I I I I I I I I I I I I — I I I I I — I I I I I I I 



60 120 180 240 300 360 4 20 



TIME (minutes) 



Figure 6. — Slow response to temperature change. These fishes 

 changed their selected temperature over more than 2 h in the 

 experiments. Symbols as in Figure 4. 



that the fish would eventually select, independent 

 of their acclimation temperatures. Topsmelt, 

 however, did not show this pattern, for their initial 

 selected temperature gave a good indication of 

 their preference and was independent of their ac- 

 climation temperature (Ehrlich et al. in press). 

 Doudoroff (1938) also found that fishes did not 

 select the temperatures to which they had been 

 acclimated but rather selected a common range of 

 temperatures, which he suggested must have 

 some physiological significance. 



Figures 4-6 show that the final preferendum 

 was reached within several hours after the estab- 

 lishment of the gradient. This is considerably less 

 time than the approximately 24 h reported by 



844 



