Summary The osmoregulatory system was studied in wild adult and reared juvenile Acipenser persicus to determine the effect of habitat and salinity on the ionic system. The mean osmolarity in blood serum of sturgeons from the Caspian Sea, estuary, the Kouraneski ponds and the rearing tanks were 305.3 ± 14.3, 308.7 ± 25.8, 265.0 ± 19.1 and 259.3 ± 8.8 mosmol/L, respectively. The mean concentrations of Na + were 151.2 ± 6.3, 152.2 ± 8.4, 142.5 ± 5.9 and 131.4 ± 4.1 meq/L, whereas mean concentrations of K + were 2.7 ± 0.9, 3.6 ± 0.9, 3.1 ± 0.5 and 2.6 ± 0.5 meq/L, respectively. The determined concentrations for Magnesium ion in fish of the four studied origins were 1.5 ± 0.2, 1.5 ± 0.3, 0.8 ± 0.2 and 0.7 ± 0.2 meq/L, respectively and those for Calcium were 2.31 ± 0.51, 2.61 ± 0.51, 1.85 ± 0.58 and 1.46 ± 0.43, respectively. The Pearson’s correlation coefficient and regression equations indicated that Mg ++ (r = 0.38) and Na + (r = 0.41) are among the effective ions to influence the blood serum osmotic pressure in A. persicus in brackish water and fresh water, respectively. The study also looked at potential differences between males and females, however the osmotic pressure in blood serum were habitat but not sex dependent.