Evaluation of acute toxicity of carbaryl and malathion to freshwater teleosts, Channa punctatus (Bloch) and Heteropneustes fossilis (Bloch).

Bioassay tests evaluated the acute toxicity of carbaryl (a carbamate) (50% wettable powder, W.P.), and malathion (50% E.C.) (an organophosphate) (50% emulsifiable concentrate; E.C.) by determining their LC50 and the acute toxic ranges for 24, 48 and 72, and 96-h exposure to Channa punctatus (Bl.) and Heteropneustes fossilis (Bl.). Regression equations and slope functions were determined for different time periods. The relative susceptibility of the fish, the relative toxicity, and the safe concentrations of these biocides were calculated on the basis of LC50 for 96 h. C. punctatus was found to be relatively more susceptible to both the compounds, while malathion was the more toxic of the two biocides.