Indicators of Osmotic and Ion Regulation in the Fish of the White Sea

The osmotic concentration; the concentrations of sodium and potassium; the content of total, free, attached water fractions in plasma; and the content of interstitial and cerebrospinal fluid, in the brain, muscles, liver, and erythrocytes typical for the fish in the native environment were determined for cod Gadus morhua . Under stress, a protective reaction is implemented, it prevents tissue dehydration by increasing the osmotic concentration in the interstitial fluid in the European flounder Platichthys flesus , spotted wolffish Anarhichas minor , lumpsucker Cyclopterus lumpus, and short-horn sculpin Myoxocephalus scorpius . The osmotic concentration preconditioned by inorganic ions in the muscles, liver, and erythrocytes of cod is significantly lower compared to the internal environment. The lack of ions in the tissues is compensated by the accumulation of organic osmolytes. Similar patterns are observed in euryhaline species when acclimated to the marine environment and in freshwater fish in the zone of critical salinity. Values of the osmotic concentration and sodium and potassium content in the blood plasma and tissues of the White Sea fish refer to the corresponding regulation ranges obtained for euryhaline and freshwater fish in the salinity range compatible with life activity.