CHANGES IN CORTISOL DYNAMICS IN WILD AND HATCHERY-REARED JUVENILE COHO SALMON (ONCORHYNCHUS-KISUTCH) DURING SMOLTIFICATION

Cortisol dynamics were examined in hatchery and wild juvenile coho sal mon (Oncorhynchus kisutch) over the spring of 1991 and 1992 when the f ish were smelting. Wild fish were caught in the upper Quinsam River, B ritish Columbia and at the downstream enumeration fence when they star ted to migrate. Two groups of hatchery fish were from the top and bott om ends of an earthen rearing channel. Plasma cortisol levels increase d during the spring in all groups, but were significantly greater in w ild than in hatchery smelts. The half-life of plasma cortisol decrease d as fish smelted; however, there was no difference among the groups. Corticosteroid receptor (CR) concentration and affinity decreased duri ng the spring. Wild fish consistently possessed the greatest gill conc entration of CR. The change in dissociation constant (k(D)) was simila r for hatchery and wild fish during spring 1991. In 1992, hatchery fis h showed a similar gradual increase. In contrast, wild fish did not sh ow an increase in k(D) until May. The changes in cortisol concentratio n in the plasma and the CR k(D) occurred synchronously with the increa se in Na(+)K(+)ATPase activity in wild fish, which showed the greatest increase in k(D), plasma cortisol, and Na(+)K(+)ATPase activity.