Rainbow trout (Oncorhynchus mykiss) exposed to oxygen supersaturation and handling stress: Plasma cortisol and hepatic glutathione status

Three groups of one summer old rainbow trout were exposed for 22 days eithe r to normoxia (100%) or moderate oxygen supersaturation; 120% and 140%. Aft er the exposure, all groups were transported for three hours in hyperoxic c onditions (123% O-2) thus simultaneously experiencing density and handling stress. The recovery of rainbow trout to multiple stressors was measured in normoxic conditions. Moderate oxygen supersaturation did not have any nega tive effects on growth, feed conversion and blood hematology measured over 22 days. On the other hand, the combined effects of the stressful environme nt in the fish farm and oxygen supersaturation resulted in a 3-fold increas e in plasma cortisol levels in those with 100% and 120% O-2 supersaturation and a 2-fold increase in the 140% supersaturation group. Furthermore, the stress response after transportation was lowest in the 140% group 24 hours after recovery but highest after 70 hours. Moderate hyperoxia or transporta tion stress did not change glutathione concentrations in liver indicating t hat routine sampling does not affect hepatic glutathione status. Our result s indicate that moderate O-2 supersaturation (<140%) could be considered as feasible in cultivation of rainbow trout since no harmful effects were fou nd.