Acute Toxicity and Ethological Responses of Channa punctatus (Bloch) Exposed to an Organophosphorus Insecticide, Dimethoate

Dimethoate is a commonly used pesticide in the agricultural land.The present investigation was undertaken to evaluate the acute toxicity of dimethoate, an organophosphorus insecticide, in freshwater fish Channa punctatus (Bloch) and to study a relative behavioural changes after exposing for 24, 48, 72 and 96 h.The regression equation calculated for 24, 48, 72 and 96 h was found as Y= -0.50+9.05X,Y= -0.12+8.21X,Y= 0.27+7.45Xand Y= 0.68+7.64X,respectively whereas the LC50 value calculated after 24, 48, 72 and 96 h was at 1.136, 1.034, 0.921 and 0.817 ml/L, respectively.During the static bioassay test, water quality parameters showed slight fluctuation indicating that the mortality of test fishes occurred due to pesticide exposure and not due to alterations in water quality.During dimethoate exposure, fish showed various ethological responses such as faster opercular movements, convulsions, excessive mucus secretion and loss of equilibrium or imbalanced swimming.Prior to death, the clinical signs like pale body colour and hemorrhagic patches over the body were noticed which become progressively more prominent up to the end of the experiment.Result of this investigation showed that dimethoate pesticide is potentially toxic to Channa punctatus so, the natural waterbodies must be monitored at regular interval to reduce the impact across food chain.