EFFECT OF MALATHION ON THE OPTOMOTOR BEHAVIOR OF BLUEGILL SUNFISH, LEPOMIS-MACROCHIRUS

1. Behavioral changes are very good and sensitive indicators of pollution by any toxicant. The optomotor responses are useful to quantify the changes in some of the movement patterns of the fish. 2. The present study deals with the behavioral changes of bluegill sunfish, Lepomis macrochirus, that result from an exposure to 0.002, 0.004, 0.008, 0.016, 0.032 and 0.048 ppm of malathion. 3. Malathion belongs to the widely used group of organophosphorus pesticides. Alterations in behavior due to an exposure to sublethal concentrations of malathion were estimated by measuring two parameters namely "following" and "reversal" which involve two optomotor responses. 4. A specially constructed apparatus with a jar containing water to hold the fish around which was a rotating patterned drum was used to measure the optomotor response. 5. All 90-degrees changes in movements or turns, referred to as "quarter turns", made by the fish in the direction of the drum rotation ("following") or opposite direction ("reversal") were recorded. 6. At 0.016 ppm exposure level the fish became hyperactive and at 0.048 ppm exposure level they became lethargic. 7. The mean scores for "following" was significantly (P < 0.0001) different at 0.016, 0.032 and 0.048 ppm exposure concentration compared to control, 0.002, 0.004 and 0,008 ppm exposure concentrations. 8. The mean "reversal" scores showed more or less the same trend. 9. There was a significant (P < 0.000 1) increase in "reversals" at 0.0 16 ppm compared to control and fish exposed to various other concentrations. 10. Behavioral studies may be used to quickly assess and evaluate the effects of sublethal doses of pollutants that are found in very small quantities in the aquatic environment.