Physiological changes in Labeo rohita during nitrite exposure: Detoxification through dietary vitamin E

This study investigated the effect of sub-lethal nitrite–nitrogen exposure on Labeo rohita. Fishes fed with different levels of vitamin E (VE) for 60 days were exposed to nitrite for another 45 days with same feeding regime. There were four treatment groups, viz., VE₁₀₀− N, VE₁₀₀ + N, VE₁₅₀ + N and VE₃₀₀ + N. After 45 days of exposure, lowest specific growth rate was observed in VE₁₀₀ + N and highest in VE₁₀₀− N. Reno-somatic index and methaemoglobin reductase activity were significantly increased by nitrite exposure. Highest Hb and Hct were observed in VE₁₀₀− N and significantly decreased upon nitrite exposure. Significant differences were observed in the activities of catalase and SOD as well as serum potassium and chloride levels among different treatments. However, serum calcium and osmolality was not significantly varied. Nitrite exposure caused marked increase in nitrite concentration in gill, liver and muscle. In liver and muscle dietary supplementation of higher amounts of VE found to reduce nitrite accumulation. It was noticed that nitrite exposure has adversely affected growth, haematological variables, ionic balance and dietary supplementation with additional amounts of VE found to overcome the adverse effects of nitrite–nitrogen. Detoxification of nitrite by methaemoglobin reductase system was enhanced by dietary supplementation of additional amounts of VE.