In this study, circumstances of osmoregulation system of the Persian sturgeon released in the Gorgan River in order to stock restoration have been investigated. Ten days old larvae sampled during 45 days from hatchery to the estuary. Samples taken form blood serum, gills and kidney tissues were collected from 12 May to 26 June, 2003. In the present study, Sampling sites were Shahid Marjani sturgeon hatchery, earthen pond, river water ( 2 sub samples ) and estuary. The blood serum osmotic pressure ( mOsm/L) , K^ + , Na^+, Mg^++ ( mEqu/l) and Ca^++ (mg/dl) concentration were measured. In order to investigate the condition of osmoregulatory cells development, histological experiments of the specific tissues have been taken place accordingly.Regarding to figs. (1,2,3,4,5,6,7,8,9,10) , osmotic pressure of blood plasma was higher than the water ( the difference range is 14- 196 mOsmol/l). Statistical results (test of one way t student ) show significant differences between the medium osmotic pressures ( P=0.99). In cases of ions, the concentration of Na^+ and K^+ were higher than those of the water. There is also significant difference between these ions concentration ( = 0.01).In contrast, the content of Mg^ ++ and Ca^++ were lower than the water. Regarding to these last two ions, there is also significant difference ( P= 0.99). Histological experiments confirm the results and show a relative development of the osmoregulatory cells in gills and kidney in accordance with fish ages.

Iranian Fisheries Science Research Institute

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