The capability of ion_ osmoregulation and salinity tolerance on juvenile Acipenser persicus (Borodin, 1897)

The ion_ osmoregulation and salinity tolerance capabilities of juvenile Acipenser persicus of different age and size groups with 90 fry for each treatment in freshwater (FW: < 0. 5 ‰)، estuary water (EW: 9. 5 ‰) and the Caspian Sea water (CSW: 12. 5 ‰) were investigated. The fishes are directly transferred from FW to EW and CSW. The possible repercussions of ion_osmoregulatory processes on some classical indicators were examined at the end of 168 hours fish acclimation. Mortality was observed in different groups in CSW. The levels of osmolarity and ion concentration (Na+، K+، Ca+2 and Mg+2) in the plasma were determined. The trend of increasing levels of ion and osmolarity were observed at higher salinity in each group (p<0. 05). The functional levels of the mechanism of osmotic and ionic homeostasis were similar in different groups but differed in experimental media (p<0. 05). Significant differences were observed between the levels of plasma Na+ concentration in different groups in EW and CSW media (p<0. 05). Plasma Na+ and Ca+2 concentrations were higher than those of FW and EW media، but lower than in CSW media. However osmolarity and ion concentration values did not return to initial values (p<0. 05)، showing that osmoregulatory processes caused physiological changes in this species.