Gill (Na+K)-ATPase activity and plasma thyroxine concentrations do not predict time of release of hatchery coho ( Oncorhynchus kisutch) and chinook salmon ( Oncorhynchus tshawytscha) for maximum adult returns

Abstract

The timing of cyclic changes in gill (Na+K)-ATPase activity and plasma thyroxine (T 4) concentrations in coho ( Oncorhynchus kisutch) and spring chinook ( O. tshawytscha) salmon were compared with the time of release from hatcheries promoting maximal survival. In coho salmon from Big Creek reared in the laboratory, thyroxine reached a maximum concentration in April, and gill (Na+K)-ATPase activities reached a maximum in May. Plasma thyroxine in coho salmon reared at Big Creek Hatchery had two peaks in concentration in April and mid-May. Only fish released in June had a peak in gill (Na+K)-ATPase activity in mid-May. Coho salmon reared at Cascade Hatchery showed no cyclic changes in either plasma thyroxine or gill (Na+K)-ATPase activity. Greatest returns from coho salmon released from Big Creek Hatchery and from Cascade Hatchery occurred from fish released in June. Juvenile spring chinook salmon reared at Cole Rivers Hatchery had peaks in gill (Na+K)-ATPase activity in June or July, September, and November. In the same strain of fish reared in the laboratory, gill (Na+K)-ATPase activity reached a peak in October, and thyroxine concentration reached a maximum in November. Greatest adult returns occurred in fish released from Cole Rivers Hatchery in August. Spring chinook salmon reared at Round Butte Hatchery had variable peaks in gill (Na+K)-ATPase activity, depending on the year and rearing conditions. The time of release providing greatest adult returns did not correlate well with peaks in gill (Na+K)-ATPase activity. Results from these studies indicated that gill (Na+K)-ATPase activity and plasma T 4 levels were poor predictors for release of juvenile coho and spring chinook salmon to produce maximal adult returns. The relationship of oceanic factors to survival of hatchery fish is discussed.