ACCLIMATION STATES OF JUVENILE STRIPED BASS 705 



photoswitch to reproduce the seasonal photoperiod. The remaining 

 three tanks of fish were maintained at constant temperatures of 15, 

 20, and 25° C. The fish were acchmated for 17 days in the 

 fluctuating and constant temperature regimes from Nov. 18 to 

 Dec. 4, 1975. During this period the bass were fed freeze-dried brine 

 shrimp three times a day. Fish were not fed 6 hr before or during the 

 day of testing. On Dec. 5, 1975, critical thermal maximum (CTMax) 

 values were determined for a pair of fish from each tank at 0000, 

 0600, 1200, 1800, and 2400 hr. This block design provides ten 

 observations for analysis at each temperature and time-of-day 

 treatment. The CTMax values were determined by heating 4 liters of 

 water at a rate of 1.5°C/min until the bass therein permanently lost 

 equilibrium. 



In the second phase of the experiment, the fluctuating regimes 

 were modified to provide one, two, and six cycles in each 24-hr 

 period, having the same degree (±5°C) of fluctuation around the 

 same 20°C base temperature. The constant-temperature (15, 20, and 

 25° C) tanks were retained. The average weight of striped bass used in 

 this phase was 10.8 g, and the average total length was 8.7 cm. After 

 15 days of acclimation (on Jan. 16, 1976), the test procedure 

 described previously was repeated. 



When the small fishes used in the second phase of experimenta- 

 tion were subjected to the most rapid temperature changes used in 

 the study (6 cycles/24 hr), the estimated difference between their 

 internal (gut) and external water temperature was small (Fig. 2). The 

 smaller fish (6 to 7 g) tested in the initial phase are estimated to 

 exhibit even smaller degrees of temperature lag since they were 

 acclimated at 1 cycle/24 hr. These slower rates of change, combined 

 with the smallness of the fishes, could only produce insignificant 

 differences between body and cycling water temperatures. 



The test fish were obtained as fry from the Tennessee Wildlife 

 Resource Agency's fish hatchery in Morristown, Tenn., and were 

 raised to experimental size in our laboratory. They were the progeny 

 of spawning stock collected from a landlocked, freshwater popula- 

 tion in Cherokee Reservoir, Tennessee. 



RESULTS 



The mean CTMax values for the initial constant and fluctuating 

 acclimation regimes increased in the order 15, 20, and 15 to 25(— ) 1 

 cycle/24 hr; 15 to 25(+) 1 cycle/24 hr; and 25°C (Table 1). Analysis 

 of variance (ANOVA) indicated significant differences among these 

 acclimation temperature responses (P < 0.01), and Duncan's new 



