Brain acetylcholinesterase activity and optomotor behavior in bluegills, Lepomis macrochirus exposed to different concentrations of diazinon.

Organophosphorus pesticides inhibit acetylcholinesterase (AChE) activity to varying degrees in different species of fish. Estimation of AChE activity is a useful tool for establishing the degree of pollution caused by these pesticides. Behavioral changes are very good and sensitive indicators of any chemical pollution. Changes in the optomotor behavior are easily quantifiable. Therefore estimation of AChE activity and changes in the optomotor response are taken as criteria to study the effects of different concentrations (15, 30, 45, 60 and 75 micrograms/l) of diazinon, an organophosphorus compound, in bluegill Sunfish, Lepomis macrochirus. The fish were exposed for a period of 24 hours. In this study, AChE activity showed a significant decline above an exposure concentration of 45 micrograms/l exposure concentration. In the case of optomotor behavior, a decline in the scores of the "following" responses of the fish was noticed from an exposure concentration of 30 micrograms/l. It seems that a behavioral bioassay is more sensitive than other types of testing.