Peculiarities of osmoregulation of circulating red blood cells in steno-and euryhaline marine fish species under hypoosmotic conditions

The peculiarities of osmoregulation of circulating red blood cells of the stenohaline giant gobyGobius cobitis and the euryhaline toad gobyGobius batrachocephalus have been studied under experimental conditions. In the giant goby, volume of the red blood cells increased steadily by 10.6–18.1% (p < 0.05) after reduction of the medium salinity from 15–17 to 6.0–6.8‰ and this volume increase remained during the entire experimental period (40–45 days). Lysis of red blood cells was noticed in some cases, which was indicated by a decrease of the number of red blood cells and an increase of concentration of free hemoglobin in the blood plasma. No similar reactions were observed in the euryhaline toad goby; the mean cell volume did not change statistically significantly. The volume regulation resulted in K+ efflux from red blood cells. The blood red cells of the toad goby had a high resistance to osmotic stress. The Na+,K+-ATPase activity in the red blood cell membranes of the toad goby was higher by 18.8% (p < 0.001) than in the giant goby.