Effects of salinity on mortality, growth performance, blood traits and gill histopathology of snowtrout, Schizothorax zarudnyi

Salinity is one of the important environmental factors affecting fish. To determine the effect of different aspects of salinity increase, it is important to determine the maximum salinity tolerance of fish. The salinity tolerance of Hamun mahi (Schizothorax zarudnyi) juveniles was evaluated in the laboratory by gradual and abrupt salinity increases. The mortality, behavior, gill histopathological alternations and chloride cells numbers were evaluated in the fish. In addition, fish were cultivated in 10 g/L for 20 days and at the end of the rearing period, their growth and blood factors were measured. LC50 value (lethal concentration) 24, 48, 72 and 96 hours were 11.44, 10.72, 10.52 and 10.52 g/L, respectively. The gradual transfer of fish to higher salinities resulted in an increase in the salinity tolerance (13g/L). The most observed changes in gill tissue included epithelial lifting (65%) and the smallest observed change was necrosis (14%). Also, the number of chloride cells increased by 16% after exposure to LC50 (96-h) concentration. There was no significant difference in growth rate, total protein, AST, ALP, and cortisol in fish reared in fresh and 10 g/L salt water, while glucose and triglyceride showed a significant difference. In general, the results of this study showed that it is possible to cultivate Hamun mahi in salt water (10 g/L), but due to the low growth of this fish during the cultivation period additional studies are needed to find a proper rearing condition.