FISHERY BULLETIN: VOL. 72, NO. 4 



fish had a 0.7°C increase in preferred range 

 following exposure. 



Use of tunnel passes as an index of locomotor 

 activity is discussed by Beitinger et al. (in press). 

 The diurnal activity pattern continued after treat- 

 ment in all three groups (Figure 2). Immediately 

 subsequent to treatment, a marked decrease in 

 activity occurred in cold- and heat-treated fish 

 but not in the control group (Figure 2). This 

 decrease might help explain the increased 

 susceptibility of thermally shocked fish to 

 predation reported by Coutant (1972a, b, 1973) 

 and Sylvester (1973). Hocutt (1973) found that 

 exposure to rapid temperature changes, as large 

 as 12°C below and 8°C above ambient tempera- 

 tures, resulted in decreased swimming perfor- 

 mance in juvenile largemouth bass, Micropterus 

 salmoides; spotfin shiner, Notropis spilopterus; 

 and channel catfish, Ictalurus punctatus. 



Due to their mobility and acute temperature 

 sensitivity, fishes are able to avoid environments 

 of unfavorable temperatures. If trapped at these 

 temperatures, fish possess the ability to resist 

 thermal death. Ecologically, resistance ability 

 affords a fish the opportunity to escape potentially 

 lethal conditions at least until they lose 

 equilibrium. Fish are exposed to stressful 

 conditions when existing within their thermal 

 resistance zone or when experiencing large tem- 

 perature changes. The major objective of this 

 research was to examine the thermoregulatory 

 performance of bluegill following "high" and 

 "low" thermal exposure. Nevertheless, the 35% 

 mortality among 36.1°C treated fish and the se- 

 vere depression in immediate posttreatment ac- 

 tivity of both the 21.0° and 36. 1°C treated fish were 

 the two most ecologically important findings. All 

 fish surviving treatment retained the ability to 

 behaviorally thermoregulate, hence, disruption of 

 thermoregulatory behavior is not a likely outcome 

 of thermal shock in fishes. 



ACKNOWLEDGMENTS 



I wish to thank John J. Magnuson, William H. 

 Neill, Charles C. Coutant, and Robert F. Carline 

 for their valuable reviews of the manuscript. 

 Technical assistance was provided by William 

 R. Shaffer, Gerald G. Chipman, and Sharon A. 

 Klinger. This study was jointly supported by the 

 National Oceanic and Atmospheric Adminis- 

 tration's office of Sea Grant through an insti- 



tutional grant to The University of Wisconsin 

 and by the Madison Gas and Electric Company. 



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