Effect of sub-lethal nitrite on selected haematological parameters in fingerling Catla catla (Hamilton)

A sub-lethal nitrite toxicity trial was conducted using static conditions for a period of 96 h with fingerlings of Catla catla (21.4+-3.6 g). Fingerlings were exposed to five concentrations of nitrite, that is, 1, 2, 4, 8 and 10.4 mg L-^1 and a nitrite-free control to study changes in haematological parameters. Nitrite caused an increase in immature erythrocyte population (724%) in lower concentrations (0-4 mg L-^1) at 6 h while they were absent in higher concentrations. The total erythrocyte count was reduced at 6 h followed by an increase at 12 h with further reduction up to 96 h in all concentrations of nitrite. The 96-h exposure resulted in 21.2-31.8% reduction in erythrocyte population in 1-10.4 mg L^-1 nitrite. The haemoglobin content decreased progressively with increasing nitrite concentrations as well as exposure periods. Total leukocyte count decreased initially at 6 h in all treatments followed by an increase after 12 h, signifying development of a protective response of the body to nitrite stress. Blood glucose decreased initially up to 24 h followed by an increase through 96 h. Serum protein level decreased continuously with increasing exposure period. The study revealed that exposure to nitrite caused changes in almost all the haematological parameters in the fingerlings depending on the concentration as well as exposure period. Nitrite being one of the important inorganic nutrients often recorded at higher levels in intensively cultured ponds, the present study highlights its adverse impact on fish and stressed the need for the management of this nutrient in culture ponds.