Effect of sublethal concentrations of Malathion on the behaviour of Heteropneustes fossilis

Abstract

The present study was performed to investigate the impact of sublethal concentrations of malathion on different behavioural aspects of Heteropneustes fossilis. LC₅₀ of malathion for 96 hrs by static bioassay test was found to be 21.34 µl/L .The fishes were exposed to three different sublethal concentrations (2.13µl/L, 1.07 µl/L and 0.71 µl/L) for 21 days. Malathion exposure caused decrease in resting period, increase in opercular movement and air gulping, increase in S-jerk, threat and burst swimming behaviour. Slow response during feeding, swimming on the upper surface of water hanging vertically, spreading   throughout aquarium was also observed in pesticide treated fishes. In the highest concentration i.e. 2.13µl/L mortality of fishes occurred. Fishes died with bending of the mid section of the body and opening mouth. Fishes lay down motionless at the bottom of the aquarium before death. Fading of body colour was also observed in malathion treated fishes. These results suggest that sublethal concentrations of malathion has negative impact on the behavior of Heteropneustes fossilis.