The activity of acetylcholinesterase (AChE) in the vital organs of fish such as gill, liver, muscle, kidney and brain of the freshwater common carp Cyprinus carpio (C. carpio) was investigated after exposing to acute lethal toxicity (ALT) and chronic sublethal toxicity (CST) of phorate. C. carpio fish were exposed to ALT (LC 50 /96 hours -0.71 ppm/l) of Phorate for one day and 4 days and CST (one-tenth of the LC 50 /96 hours -0.071 ppm/l) of Phorate for 1, 7, 15 and 30 days and the concentration related differences in the inhibition and recovery of the AChE enzyme activity was evaluated in the target organs of the fish. Relative to controls, the activity of AChE in all the organs of the fish exposed to ATP gradually decreased significantly ((P<0.05)) at 1 and 4 days of exposure period whereas in the fish exposed to CTP the AChE activity was elevated at day 1 and gradually decreased from day 7 to day 15 followed by an increase at day 30 in all the organs significantly (P<0.05). Based on the percent values obtained the inhibition of AChE activity was predominantly more in the organs of the fish exposed to ATP in a concentration-dependent manner. On prolonged exposure for 30 days in CTP the AChE activity was restored gradually depending on the initial pesticide exposure concentration.Findings from this study have demonstrated that inhibition of AChE activity in C. carpio is a useful biomarker for assessment of anticholinesterase pesticide contaminations in water.

The present study is aimed to investigate the acute and chronic toxicity stress of phorate, induced alterations in the activity levels of Succinate dehydrogenase (SDH), a vital enzyme of citric acid cycle that catalyses the reversible oxidation of succinate to fumarate. Freshwater fish Cyprinus carpio (C. carpio) were exposed to acute lethal toxicity (LC 50 /96 hours -0.71 ppm/l) of Phorate (ALTP) for one day and 4 days and chronic sublethal toxicity (one-tenth of the LC 50 /96 hours -0.071 ppm/l) of Phorate (CSTP) for 1, 7, 15 and 30 days. After the completion of stipulated exposure period the SDH enzyme activity levels were estimated in the vital organs of fish such as gill, liver, muscle, kidney and brain. The activity of SDH in all the organs of the fish exposed to phorate decreased at 1 and 4 days of exposure in acute toxicity in the order, day 1>4. The decrease was more at day 4 than at day 1. In the fish exposed to chronic toxicity of phorate (CTP), in the activity of SDH from day 1 to day 7 there was increase in the decrement but from day 7 to day 30 it was regressed in all the organs of the fish in the order, day 1>7<15<30. The differences in the SDH activity between controls and experimental were found to be statistically significant (P<0.05). The present study indicates the phorate induced alterations in the activities of carbohydrate metabolic enzyme caused significant metabolic effect on the physiological consequences.