Effects of cortisol and salinity acclimation on Na+/K+/2Cl–- cotransporter gene expression and Na+, K+-ATPase activity in the gill of Persian sturgeon, Acipenser persicus, fry

Na+, K+-ATPase activity and Na+/K+/2Cl–- cotransporter (NKCC) gene expression in the gills of Persian sturgeon, Acipenser persicus, fry (2-3 g, 3.30-8.12 cm total body length) in freshwater (control group), diluted Caspian Sea water (5 ppt) and after treatment with cortisol in freshwater were studied. Na+, K+-ATPase activity was lower in the 5 ppt-acclimated fish (1.07±0.05 _mol Pi/mg protein/h) than in the control fish (1.19±0.05 μmol Pi/mg protein/h) but this difference was not significant. nKCC gene expression in the 5 ppt-acclimated fish (1.6±0.07) was significantly higher than in the control fish (0.8±0.00). In the cortisol treated fish, Na+, K+-ATPase activity (1.91±0.05 μmol Pi/mg protein/h) and NKCC gene expression (3.2±0.1) were significantly higher than in the control group. our results show that Persian sturgeon fry (2-3 g) can tolerate 5 ppt salinity by changing their enzymatic content and activity, and that exogenous cortisol application can increase the osmoregulatory capacity of fry before release into brackish water and can reduce their mortality.