Acute toxicities of commercial grade malathion (EC50) on Esomus danricus were determined by static-with-renewal tests and found to be 0.026, 0.022, 0.02 and 0.017 mgl-1 respectively for 24, 48, 72 and 96 hours. During acute toxicity, the normal colour was found to fade, along with copious mucous secretions, irregular, erratic and jerky movements. Three sub lethal doses (0.0017, 0.00017 and 0.000017 mgl-1) were taken for determining changes in growth, somatic indices and oxygen consumption at weekly interval for 28 days. A decline in body weight accompanied by a dose and exposure dependent increase in hepato-somatic index and decline in brain and kidney-somatic indices were observed. Decline in rate of oxygen consumption in 0.0017, 0.00017 and 0.000017 mgl-1 malathion exposed fish for 7 days were 33, 28 and 10%; for 14 days were 49, 43 and 17%; for 21 days were 55, 50 and 31% and for 28 days were 69, 57 and 41% respectively.
Pesticide pollution in aquatic environment brings about sudden and drastic changes in aquatic organisms. The indiscriminate use of pesticides in agricultural operations affects the aquatic environment to a greater extent. Pesticides like endosulphan and monocrotophos which are widely used in agriculture affect fish population drastically. In the present study the effect of monocrotophos on the enzymes Acid Phosphatase, alkaline phosphatase and lactate dehydrogenase of Ctenopharygodon idella has been estimated. The activity was found to be decreased significantly due to Pesticide intoxification.