Elevation of plasma cortisol during the spawning migration of landlocked kokanee salmon (Oncorhynchus nerka kennerlyi)

Kokanee salmon (Oncorhynchus nerka kennerlyi), a landlocked subspecies of s ockeye salmon, exhibited hypothalamic-pituitary-interrenal (HPI, adrenal ho mologue) axis activation and an increase in plasma cortisol concentration u p to 639 +/- 55.9 ng/ml in association with upstream migration in the upper Colorado River even though they were not exposed to a change in salinity a nd lengthy migration. Kokanee salmon were collected at various stages of mi gration and concomitant sexual maturation. The pattern of cortisol elevatio n in kokanee is similar to that in ocean-run sockeye salmon (O. nerka nerka ). The presence of plasma cortisol elevation in an upstream migrating, land locked Pacific salmon suggests that stressors previously considered to caus e the cortisol increase, such as long-distance migration and changes in sal inity, may not be primary causes of the HPI axis activation. (C) 2000 Elsev ier Science Inc. All rights reserved.