ACCLIMATION STATES OF JUVENILE 

 STRIPED BASS HELD IN CONSTANT 

 AND FLUCTUATING TEMPERATURE 

 REGIMES 



D. K. COX 



Environmental Sciences Division, Oak Ridge National Laboratory, 

 Oak Ridge, Tennessee 



ABSTRACT 



Sinusoidal temperature fluctuations of varying periodicities caused juvenile 

 striped bass, Morone saxatilis, to have acclimation states higher than the 

 constant average temperatures but lower than the maximum temperatures of the 

 cycles, on the basis of determinations of critical thermal maximums. More rapid 

 cycling caused higher acclimation states. There were no effects of time of day or 

 illumination. Heat tolerance of fish from thermally fluctuating environments will 

 likely be underestimated if average environmental temperatures are assumed to 

 I'epresent the acclimation state. Also, tolerance data developed at constant 

 acclimation temperatures will underestimate survival in fluctuating temperature 

 regimes. 



Prediction of power plant impacts and establishment of regulatory 

 standards frequently rely on laboratory data. Thermal responses in 

 the laboratory have traditionally been estimated from constant 

 temperature regimes, but temperatures in a natural aquatic system 

 are characteristically subject to diurnal and seasonal fluctuations. 

 Therefore it is necessary to determine whether reasonable predictions 

 of responses of fish to fluctuating temperature regimes can be made 

 from data developed at constant acclimation temperatures. This 

 investigation compared temperature acclimation patterns developed 

 in fish in fluctuating temperatures with those developed in constant 

 temperatures. Equilibrium loss at high temperatures was the measure 

 of acclimation state, and young-of-the-year striped bass was the test 

 species. Possible differences in thermal tolerance caused by the time 

 of day testing occurred were also investigated. Information on the 



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