PLASMA-LEVELS OF LACTATE, POTASSIUM, GLUCOSE, CORTISOL, GROWTH-HORMONE AND TRIIODO-L-THYRONINE IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) DURING EXERCISE AT VARIOUS LEVELS FOR 24-H

To examine the initial hormonal and metabolic changes in exercising fi sh, rainbow trout (Oncorhynchus mykiss) were subjected to moderate (1. 5 body lengths/s) or low (0.5 body lengths/s) water Velocities for 24 h and compared with unexercised controls. Blood sampling occurred imme diately before (0 h) and at 1, 2, 4, 8, and 24 h after the onset of ex ercise for determination of plasma concentrations of lactate, potassiu m, glucose, cortisol, growth hormone, and triiodo-L-thyronine (T-3) Th ere was no effect of either exercise or time on plasma lactate levels in any of the three groups, indicating that neither exercise regime in duced anaerobic conditions. Within the first 2 h of exercise, plasma, K+, glucose, cortisol, and growth hormone levels were all significantl y (P < 0.05) elevated over controls in the moderate-exercise group. By 4 h, none of these parameters were significantly different from contr ols except plasma K+ levels, which remained significantly higher throu ghout the experiment. There were no differences between 0 and 24 h of exercise in any parameters of any of the groups, again with the except ion of plasma K+ levels in the moderate-exercise fish, which were sign ificantly higher at 24 h. It is concluded that the effects of the onse t of exercise resemble those described far acute stress in fish. Furth ermore, short-term (24 h) exercise at moderate levels (1.5 body length s/s) resulted in continuously elevated plasma K+ levels, but did not s eem to cause similar increases in the other parameters.