Difference between summer and winter in gill NaK-ATPase activity and hypoosmoregulatory ability of seafarmed anadromous arctic char ( Salvelinus alpinus)

Abstract

1. 1. In July, both fish kept in seawater of 30–32‰ and 20‰ salinity (temperature 10–12°C) showed good hypoosmoregulatory ability and their gill NaK-ATPase activity was high. 2. 2. In January (30–32‰ salinity, 5°C), mean plasma Cl − concentration was 30 mM higher than that in July, and gill NaK-ATPase activity was only a half of that recorded in July. 3. 3. This difference in hypoosmoregulatory abilities recorded in summer and in winter is suggested to be due to a reversion during late summer and early autumn in the state of osmo-ionoregulatory system towards that of a freshwater-adapted fish, thus reflecting the migratory pattern of this species in nature.