CORTISOL, GLUCOSE AND HEMATOCRIT CHANGES DURING ACUTE STRESS, COHORT SAMPLING, AND THE DIEL CYCLE IN DIPLOID AND TRIPLOID BROOK TROUT (SALVELINUS-FONTINALIS MITCHILL)

In this study, groups of diploid (control) and triploid brook trout were subjected to a 5 min acute handling/confinement stress. Blood samples were collected from equal numbers of diploid and triploid fish at regular predetermined intervals, beginning prior to confinement and continuing for up to 3h after confinement. These blood samples were used for the measurement of hematocrit and plasma cortisol and glucose concentrations. The effects of cohort sampling and the diel cycle on these variables were also analysed. Except for minor differences, both groups responded similarly to the acute stress, with short-term elevations in plasma cortisol and hematocrit levels, and a more sustained increase in plasma glucose levels. No significant differences were found between diploid and triploid fish in their reactions to cohort sampling. However, the act of removing an individual from a tank caused significant changes in plasma cortisol levels in cohorts remaining in that tank (p < 0.001). Significant diel effects were observed for both ploidy groups in plasma. cortisol (p < 0.05) but not in plasma glucose or hematocrit.