Temperature affects physiological stress responses to acute confinement in sunshine bass ( Morone chrysops× Morone saxatilis)

Sunshine bass ( Morone chrysops× Morone saxatilis) were subjected to a 15-min low-water confinement stressor at temperatures ranging from 5 to 30 °C. Physiological responses were evaluated by measuring hematocrit, and plasma chloride, glucose and cortisol. Fish acclimated to 30 °C had initial glucose concentrations of 3.13 mM (564 mg/L) which were significantly lower than in fish acclimated to 5 and 10 °C (4.32 and 4.82 mM or 779 and 868 mg/l, respectively). Fish survived the conditions imposed at every temperature except 30 °C, where 15 out of 42 fish died during the stress and recovery protocol. The general pattern was an initial increase in hematocrit, followed by a delayed decrease in hematocrit and chloride, and an increase in plasma glucose and cortisol. In general, fish stressed at temperatures below 20 °C had lower and more delayed changes in plasma glucose and cortisol than fish tested at 20, 25 and 30 °C. Initial cortisol concentrations were 65 ng/ml and increased to above 200 ng/ml in fish held at 20 °C and above. At the higher temperatures, glucose concentrations were twice the initial concentration after stress and cortisol changes were four to five times the initial concentration after the stress. Quantitative responses for glucose and cortisol were moderate and recovery rapid in fish stressed at 10 and 15 °C; therefore, this range of water temperature is recommended when handling sunshine bass.