One of the most important factors to produce spawners & juveniles for marketable fish raising and conservation of stocks is to carefully understand the osmotic & ionic regulation system in fish blood serum and environment. For this purpose, during 1998.2000, 75 hatchery raised brood fishes and juveniles of Persian sturgeon (Acipenser persicus), 1 & 2 years old, were investigated in two groups in international sturgeon research institute to determine osmolarity & concentration of Na+, K +, Ca and Mg++ in blood serum of Persian sturgeons in sea, estuary and hatchery, also 133 larvae studied to measure their resistance and adaptability to determine the best age & weight of releasing. The mean of osmolarity in blood serum of the samples obtained from sea, estuary, hatchery and rearing tanks was 305.29 ± 14.33,308.72 ± 25.72, 265.03 ± 19.05 and 259.29 ± 8.78 msmol/l, respectively and the mean of Na concentration was 151 ± 631,152.16 ± 8.423 142,47 ± 5.92 and 131.7 ± 4.12 mEqgn and Mg++ 1.48 ± 0.19, 1.50 ± 0.27, 0.83 ± 0.15, 0.70 ± 0.15 mEqgn, respectively. According to data in group one, no significant difference was found in the osmolality and concentration of Na+, Ca++ & Mg in blood serum of brood fishes in sea and estuary, but there was significant difference in comparison with freshwater raised broodfishes and juveniles. Studies showed that the sex of sturgeon can not influence osmolality and concentration of ions in blood serum. According to the Person's correlation coefficient and regression equation the most important ions which determine osmolality in brackish water and fresh water are Mg ++ and Na , respectively. Although, in early days of life, age is an important factor in the development of osmoregulation organs in juveniles of Persian sturgeon, the findings obtained from 96h-120 hLC50 tests in the second group showed that weight & height of fish are the crucial factors in the next stages of life. Recent studies indicated, when the environment, nutrition, rearing culture and loading & releasing place are suitable, the sturgeon juveniles can be released in river & estuary, in early days after hatching & initiation of exogenous feed, in 33-35 days after obsorption of yolk sac, with 6.2-7.5 cm length & 1+8-2.4 g weight.

Iranian Fisheries Science Research Institute

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