Anesthetic and Handling Stress on Survival and Cortisol Concentration in Yearling Chinook Salmon (Oncorhynchus tshawytscha)

Abstract

Breif anesthetization with 50 mg/l buffered MS-222 (ethyl m-aminobenzoate methanesulfonate) of yearling chinook salmon (O. tshawytscha) during mild handling caused no change in plasma cortisol concentrations compared with levels in non-anesthetized fish. Prolonged exposure (180 min) to a depressing dose of buffered MS-222 (25 mg/l) elevated cortisol more than an immobilizing dose (50 mg/l), while 100 mg/l was lethal within 30 min. Fish anesthetized (50 mg/l MS-222) during a severe 30 min handling stress had significantly lower mortality than controls to a second handling stress applied when the fish were no longer anesthetized. Anesthetization during the 1st stressor also prevented the cortisol stress response evident in the control fish. Anesthetic (with or without buffer) administered before initial capture was most effective at increasing survival during a 2nd stressor, while anesthetic supplied after initial capture may have been slightly less effective. A 0.5% NaCl solution supplied after capture was less effective than any anesthetic treatment in increasing future survival, but was better than no treatment. Saline treatment did not attenuate the cortisol stress response. A rapid method of plasma sample preparation for competitive protein binding assay of cortisol was developed.