Content of Na+, K+, Cl–, and Ca2+ in the Blood of Juveniles of the Black Sea Trout Salmo trutta labrax under Intrapopulational Differentiation

Abstract

The content of Na⁺, K⁺, Cl^–, and Ca²⁺ in blood of farm-raised juveniles of Black Sea trout at the age 10 and 12 months, at the stage of selection of life strategy, was measured. Change in ion exchange related to smoltification in the fish kept in freshwater begins in females earlier than in males. After differentiation of parr in the smolt, the concentrations of Na⁺ and Ca²⁺ decrease and the concentration of K⁺ increases in comparison with that of the resident form. An increase in water salinity does not activate osmoregulatory restructuring of the organism. The decrease in the concentrations of Na⁺ and Cl^– in blood of the Black Sea trout may indicate the beginning of the smoltification process.