ACCLIMATION STATES OF JUVENILE STRIPED BASS 711 



clear than those for fishes (see Costlow and Bookhout, 1971; Thorp 

 and Boss, 1975). 



I suspected a synergistic effect between temperature change and 

 illumination since goldfish (Carassius auratus) maintained under 

 constant temperature conditions in the laboratory show relatively 

 greater resistance to heat during the summer and to cold during the 

 winter (Hoar, 1955). Temperature compensation is not responsible 

 for these seasonal alterations of temperature resistance. Alterations 

 of photoperiod can produce some change in thermal resistance 

 similar to the seasonal variations; the neuroendocrine system is 

 assumed to be responsible for this compensation (Hoar, 1959). 

 Therefore it would not have been surprising to find some interaction 

 between temperature change and illumination. I did not observe a 

 synergistic relationship between temperature change and illumination 

 in my study since a rise or fall in temperature during the period of 

 illumination had no apparent effect on either the rate or the extent 

 of temperature acclimation over a 17-day period. 



The results of my study make it apparent that predictions for 

 normally fluctuating situations based on static temperatures may be 

 underestimating the acclimation states of striped bass stocks. Such an 

 error would cause an underestimation of either the temperature 

 required to kill a given percentage of fish within a fixed time period 

 or the time required to kill a given percentage at a fixed temperature. 

 Prediction of such power-plant impacts as entrainment of small fish 

 in a power-plant cooling system or cold stress of fishes induced by 

 interrupting the flow of heated condenser cooling water during the 

 cool months of the year rely on thermal tolerance data for which the 

 acclimation state of the fish are known. In most cases the previous 

 thermal histories of the fishes used to develop these data have been a 

 series of constant temperatures. The use of resistance-time-to-death 

 data based on constant accHmation temperatures wUl, of course, 

 provide a more protective estimate of power-plant effects, but this 

 level of protection may be greater than is justifiable by the biological 

 data. 



The effect of artificial temperature fluctuations on the acclima- 

 tion state of fishes should be applied to the field situation with 

 caution. Temperatures in a natural system are subject to diurnal and 

 seasonal fluctuations, but mobile fish populations exhibit degrees of 

 thermoregulation that may influence the variations of temperature to 

 which they are exposed. Occasionally test fishes can tolerate brief 

 exposures to temperatures approximating or exceeding the upper 

 lethal limit (Lowe and Heath, 1969; Otto, 1974), and fish may 

 actually cycle themselves behaviorally so that near-lethal tempera- 

 tures are preferred for limited periods of the day (Lowe and Heath, 



