Clarias gariepinus (Burchell, 1822) of mean weight 320±11.2 g and total length 60.0±1.0 cm were exposed to nitrite (0.2 mg/l NO2) for 48 h at 27 and 35°C in order to investigate the effects of nitrite poisoning at these water temperatures. The effects of nitrite exposure on fish was assessed on selected haematological and biochemical indicators of the blood. The test was performed in a semi-static assay for 48 h. Fish were kept in thermostart –controlled water baths each containing 15 L of test solution. Four groups each containing 8 specimens of 3 month old C. gariepinus were exposed to nitrite at the different water temperatures. Nitrite exposed fish showed lower haematocrit value (PCV) at both experimental temperatures compared with controls. Significantly higher PCV values were recorded in fish with nitrite at 27°C (36.67±0.57%) when compared with fish at 35°C (33.33±0.57%). A significant difference was also recorded for haemoglobin level and the erythrocyte counts. Leucocyte count in fish with nitrite at 270 C was significantly higher (P<0.05) compared to the count at 35°C. For Plasma Biochemical parameters, significant differences were observed between the 2 groups for K+ concentration (27°C, 4.9±0.10 mmol/l; 35°C, 4.1±0.12 mmol/l). Statistically significant differences were observed in plasma CI- and Na+ concentrations in fish at both temperatures. It has been established from this study that nitrite is more toxic at higher temperature.
Key words: Haematology, plasma biochemistry, Clarias gariepinus, temperature.
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