The experimental material for the investigations was collected from the deep zones of the Gulf of Gdañsk. The experiments were performed at salinities of 3.0 PSU (96.87 mmol/kg), 7.3 PSU (235.73 mmol/kg), 15 practical salinity unit (PSU) (484.39 mmol/kg) and 25 PSU (807.32 mmol/kg) in conditions of hypoxia (saturation = 15% O₂), anoxia (saturation <1% O₂) and control conditions in aerated water (saturation = 100% O₂), at a constant temperature of 10°C. Hypoxia (saturation = 15% O₂) had no statistically significant effect (P > 0.05) on the osmoregulation of S. entomon in comparison with the control samples. Anoxia (saturation <1% O₂) decreased the osmotic concentration of hemolymph in S.entomon. After 6 h only at salinity 3 PSU there was a statistically significant difference between the anoxic and control samples (P < 0.05). After 96 h there was a statistically significant tendency (P < 0.05) for the osmotic concentrations to decrease in anoxic conditions at all the salinities tested except 25 PSU. A tendency was observed for the Na concentrations in the hemolymph to decrease in anoxic conditions, which was statistically significant at salinity 7.3 PSU (P < 0.05) after 96 h but not statistically significant at the other salinities tested. The results show a low concentration of K in the hemolymph of S. entomon and slight fluctuations of K concentrations, but at environmental salinities the K concentration decreases under anoxic conditions but not to a statistically significant extent (P > 0.05).