28 



Fishery Bulletin 91(1), 1993 



wa 



2PC -> 26°C 





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26°C -> 21"C 



-100 P 



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Time Since Transfer (h) 



Figure 2 



Time-course for the effect of an acute temperature change of 5°C on activity of young red drum Sciaenops ocellatus. 

 Points represent differences between means for transferred fish and control fish at the acclimation temperature. 

 Filled symbols denote periods in which activity of transferred fish differed significantly (a=0.05) from that of 

 control fish (corrected activity*!)). Left panels show upward transfers, right panels show downward transfers. 

 Small, medium, and large fish are presented from top to bottom. 



downward transfers and high controls, centered near 

 zero, that could not be detected by an overall test for a 

 temperature effect. Corrected pause frequency of both 

 small and large fish in downward transfers declined 

 throughout the experiments, relative to high controls 

 (Fig. 4). Time had a significant effect for these sizes 

 but not for medium fish. 



Pause duration 



This variable showed the greatest range of variation, 

 spanning more than two orders of magnitude (note 

 varying scales in Figs. 5&6). Small fish showed little 

 effect of time or temperature treatment on pause du- 



ration, relative to effects on larger fish. At the two 

 larger sizes, pauses were longest at the start of the 

 experiments, stabilizing after about 2.5 h. As with the 

 other behavioral measures, all main effects were sig- 

 nificant (Table 3). 



There were significant differences in pause duration 

 among time-periods for low controls and downward 

 transfers (Table 3). Linear, quadratic, and cubic trends 

 described temporal changes for small and medium fish, 

 but no trends were found for large fish. 



Controls Pause duration was generally greater for 

 fish maintained at 21° C than for those held at 26° C 

 (Fig. 5). Largest differences occurred early in the ex- 



