EFFECTS OF EARLY REARING ENVIRONMENT ON STRESS-RESPONSE, IMMUNE FUNCTION, AND DISEASE RESISTANCE IN JUVENILE COHO (ONCORHYNCHUS-KISUTCH) AND CHINOOK SALMON (O-TSHAWYTSCHA)

Coho (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) from a quaculture and wild environments were subjected to handling (30-60 s o f netting and aerial emersion) and disease challenges. Plasma cortisol concentrations ([cortisol]pl) in both coho and chinook salmon from wi ld environments were significantly elevated 4 h after handling. Coloni zed coho salmon (hatchery-reared fish, transported into a natural wate r body as fry) responded in a similar fashion to wild fish, while thos e reared entirely in the hatchery showed no significant rise in [corti sol]pl. The responses to handling stress were retained in wild and col onized coho salmon after 7 mo of hatchery rearing. A transient increas e in the leukocyte to red blood cell ratio in both wild and hatchery-r eared chinook salmon occurred 4 h after handling. Handling signficantl y decreased the antibody-producing cell (APC) number in wild fish and elevated their [cortisol]pl relative to hatchery fish. Wild fish had t he highest APC number among the three groups before the handling. No d ifference in resistance to Vibrio anguillarum was apparent in coho and chinook salmon among the different rearing environments, although chi nook salmon were generally more susceptible; disease resistance was re duced in wild coho salmon after 7 mo of rearing in a hatchery.