In the present study, the acute toxicity of chlorpyrifos (an organophosphate, OP) and cypermethrin (a pyrethroid) pesticides was estimated for 96 h in Heteropneustes fossilis. The LC50 for chlorpyrifos (CPF) and cypermethrin was found to be 1.90 mg/L and 0.085 mg/L, respectively. The acetylcholinesterase (AChE, EC 3.1.1.7) activity in Heteropneustes fossilis exposed to both the insecticides was assayed in brain, muscle and gills. In general, tissue specific as well as dose-dependent decrease in the AChE activity was exhibited by both pesticides. In response to the increasing concentrations of chlorpyrifos and cypermethrin as well, a significant decrease in the activity of AChE was found in brain while muscle and gills exhibited lesser inhibition. Thus, the brain was the main target organ for both insecticides, followed by muscle and gills. Between the two pesticides chlorpyrifos acted as more potent AChE inhibitor than cypermethrin since more intense changes in behavioral pattern was observed with the chlorpyrifos. These changes indicate that the effects of these pesticides are at neural as well as neuromuscular level.
Keywords: AChE activity; LC; behavioral pattern; chlorpyrifos; cypermethrin.