Changes in physiological indices of smolting during seaward migration of wild coho salmon, Oncorhynchus kisutch

Abstract

Wild juvenile coho salmon ( Oncorhynchus kisutch) were captured in traps or by seining during the course of parr–smolt transformation and migration from a small coastal stream in Oregon. Physiological measurements indicated that gill (Na+K)-ATPase specific activity was significantly greater in migrants than in non-migrants, but there was no significant difference in kidney (Na+K)-ATPase specific activity in the two populations. Glycogen concentrations and triglyceride concentrations were significantly lower in migrant populations than in non-migrants. Guanine concentrations tended to be lower in non-migrant fish than in migrant fish after May. There were no significant differences in plasma thyroxine or tri-iodothyronine concentrations between migrant and non-migrant fish. The decrease in energy storage compounds supports the hypothesis that migration is caused by an ionic imbalance during smolting, but the lack of changes in kidney (Na+K)-ATPase specific activity during smolting of wild fish does not support this hypothesis or the results from studies with laboratory reared coho salmon.