Plasma cortisol concentration in relation to stress in adult sockeye salmon during the freshwater stage of their life cycle

Abstract The concentration of cortisol in plasma of adult sockeye salmon ( Oncorhynchus nerka ) during the freshwater stage of the life cycle was below 5 μg/100 ml when the fish were resting in captivity. Results to date indicate that the same is true of resting salmon in their natural habitat. Handling of fish, physical exercise and disease produced highly increased cortisol concentrations. Sexual maturation and spawning did not induce sustained increases in healthy fish. Death was associated with high cortisol concentrations. Concentrations in a group of chinook salmon ( Oncorhynchus tschawytscha ), as in sockeye, increased when the fish approached death, but were in general higher than those in sockeye under comparable conditions.