Toxicity of fenitrothion to the fish Mystus cavasius and Labeo rohita

Abstract The 96-h LC 50 values (with the 95% confidence limits in parentheses) of fenitrothion for the freshwater fish, Mystus cavasius and three size groups of Labeo rohita (3 to 4·4 cm, 4·5 to 5·9 cm and 6 to 8 cm in length) were respectively 3·3 (3 to 3·5), 2·8 (2·6 to 3), 4·1 (4 to 4·2) and 4·6 (4·5 to 4·7) ppm. There was a decrease in the toxicity of the compound with increase in size, and a significant negative correlation between increasing concentrations of fenitrothion and the oxygen uptake of L. rohita . Although it is less toxic to mammals than the closely related methyl parathion, fenitrothion seems to be more toxic to fish.