The influence of water salinity and stage in life history on ion concentration of fish blood serum

(1) The Na, K, Ca, Mg concentration of blood serum have been studied in nearly 60 fish species from various waterbodies (the Neva, Lake Dal'nee, the Volga, Lake Baikal, the White Sea, the Black Sea, the Barents Sea etc.). In fishes (Cyprinidae, Percidae, Siluridae etc.) from fresh water (Lake Dal'nee, the Baikal, the Neva) with low 0.18–0.24 mEq/1 Na concentration Na content in blood serum was lower than in closely related species from fresh water (the Volga, Lyutoga River) with larger Na concentration–nearly 0.5–1 mEq 1. Blood serum of marine teleosts Na concentration (156–210 mEq/1) was higher than in migrating and freshwater species (90–174) mEq/1) and it did not depend on seawater salinity: Barents Sea–465, White Sea–255, Black Sea–227 mEq/1.
(2) Rather a considerable specific variation of ion concentration was found in blood serum of fishes from different families living in the same water body (Lake Baikal: Cyprinidae 90–95 mEq/1, Percidae 114 mEq/1, Salmonidae 126–129 mEq/1 etc.; the Volga: Siluridae 139 mEq/1, Percidae 142–150 mEq/1, Clupeidae 174 mEq/1).
(3) No relation has been detected between K, Ca and Mg concentrations in blood serum of fishes and the concentrations of these ions in the environment.
(4) Na concentration in the blood serum of sockeye salmon juveniles (101 mEq/1) migrating seaward was less than in adult fishes (132 mEq/1) returning to the lake to spawn. Na concentration in the blood of non-migrating salmonids ( Oncorhynchus nerka adult residual 104 mEq/1, Salvelinus alpinus juvenile 140 mEq/1, adult residual 141 mEq/1) changed insig- nificantly during life history. Notable hypopotassemia was observed in spawning time in Salmonidae.
(5) The comparison of blood serum ion concentration in males and females of fishes from different taxonomic groups (Acipenseridae, Salmonidae, Cyprinidae) showed no significant variation.