Toxicity of methyl parathion and fensulfothion to the fish Mystus cavasius

Abstract

The 96-h LC 50 values of methyl parathion and fensulfothion (with the 95% confidence limits in parentheses), to the freshwater fish Mystus cavasius were, respectively, 5·9 (5·4 to 6·5) and 16·5 (14·8 to 17·8) ppm. Both the pesticides induced severe morpho-anatomical deformities and behavioural changes in the exposed fish. Methyl parathion caused bloating of the stomach and softening of the ventral side. Exposure to fensulfothion resulted in lateral bending of the body. Both pesticides, at higher concentrations, affected the oxygen uptake of M. cavasius, with a progressive reduction of the oxygen consumption with increasing concentration of the pesticide. The highest concentration of methyl parathion that caused irreversible damage during the period of the respiratory experiment (i.e. 15 ppm) induced stressed and excited swimming and increased the oxygen uptake. The present paper is the first published work on the toxicity of fensulfothion to fish.