Effects of cortisol treatment on the salinity tolerance of Persian sturgeon, Acipenser persicus Juveniles

Abstract

Persian sturgeon, Acipenser persicus juveniles are annually produced and released (2-3g body weight) to the estuaries surrounding the southern parts of the Caspian Sea by hatchery centers. However, juveniles cannot withstand the salinity stress and the majority of them die before entering the Caspian Sea. In order to improve the salinity acclimation in Persian sturgeon juveniles weighing less than 2 g (1.62 ± 0.27 g; 7.4 ± 0.58 cm), the fish were treated with cortisol bath method using three different concentrations; 3, 5 and 7 mg L-1 for 24 h in freshwater. The fish were then directly transferred from freshwater to the Caspian Sea water (11‰) and sampled after 1, 4 and 9 days post-transfer. Daily mortality was recorded. Plasma osmolality, changes in the abundance and size of the Na+-K+-ATPase immunoreactive fluorescence chloride cells within the gill epithelium of the juveniles were determined. In spite of lower mortality in fish treated with higher concentrations of cortisol, plasma osmolality, chloride cells number and size in treated fish exhibited the same trends as the control (untreated) fish after 9-day post-transfer. In conclusion, cortisol treatment alone, is not directly implicated in osmoregulation and had no effect on Persian sturgeon juveniles to improve their salinity tolerance.