Plasma levels of lactate, potassium, glucose, cortisol, growth hormone and triiodo-<scp>L</scp>-thyronine in rainbow trout (<i>Oncorhynchus mykiss</i>) during exercise at various levels for 24 h

Abstract

To examine the initial hormonal and metabolic changes in exercising fish, 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 immediately before (0 h) and at 1, 2, 4, 8, and 24 h after the onset of exercise for determination of plasma concentrations of lactate, potassium, glucose, cortisol, growth hormone, and triiodo-L-thyronine (T 3 ). There was no effect of either exercise or time on plasma lactate levels in any of the three groups, indicating that neither exercise regime induced anaerobic conditions. Within the first 2 h of exercise, plasma, K + , glucose, cortisol, and growth hormone levels were all significantly (P &lt; 0.05) elevated over controls in the moderate-exercise group. By 4 h, none of these parameters were significantly different from controls except plasma K + levels, which remained significantly higher throughout the experiment. There were no differences between 0 and 24 h of exercise in any parameters of any of the groups, again with the exception of plasma K + levels in the moderate-exercise fish, which were significantly higher at 24 h. It is concluded that the effects of the onset of exercise resemble those described for acute stress in fish. Furthermore, short-term (24 h) exercise at moderate levels (1.5 body lengths/s) resulted in continuously elevated plasma K + levels, but did not seem to cause similar increases in the other parameters.