Due to its high reactivity fluoride does not occur in the element state in nature. WHO and ISO 10500 recommend that the fluoride content in drinking water should be in the range of 1.0-1.5 ppm. Fluoride ions are directly toxic to aquatic life and accumulated in the tissues where absorption rates exceed excretion rates. Duration of exposure also affects toxicity. Snake headed fish (<em>Channa </em>straitus) is larvivorous and edible fish species of India and South East Asia. After exposure of NaF (60ppm) it has been observed that body weight and organosomatic index has been decreased significantly. Some leucocytes also decreased i.e. Neutrophils 1.125-2.68%, Monocytes 0.66%-35.66%. But Lymphocytes 2.9-10.01% and eosinophils 7.6-20.88% increased. Hb% also decreased. After estimation of Catalase activity it has been observed its activity is increased in liver may be associated with increased oxidative stress. Catalase activity is decreased in brain 0.03% - 9.23%.