Na/K-ATPase Activity in Smolts of Pink Salmon Oncorhynchus gorbuscha (Walbaum, 1792) from the White Sea Exposed to Fresh, Estuarine, and Sea Water.

The Na/K-ATPase (NKA) activity in smolts of pink salmon Oncorhynchus gorbuscha (a salmon species introduced in 1959 into the rivers of the Kola Peninsula) was studied in a ten-day cage experiment with fresh, estuarine, and sea water; the fish were caught during seaward migration in the Indera River of the White Sea basin. The development of tolerance to increased salinity in pink salmon smolts was accompanied by NKA activation. In estuarine water characterized by salinity fluctuations (from fresh to sea water) and in the marine environment (28‰), the NKA activity in pink salmon smolts was significantly higher than in the individuals kept in the cages installed in fresh water. The hypoosmoregulatory ability of pink salmon fry was registered, these data indicated that smoltification in this fish species took place in early ontogenesis. The changes in NKA activity evidenced the readiness of migrating pink salmon fry for the marine phase of their life cycle.