28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Effects Of Pesticides In The Long Island Sound Lobster Mortality Sylvain De Guise1, Jennifer Maratea1, Christopher Perkins2 1 Department of Pathobiology and Veterinary Science, University of Connecticut, 61 North Eagleville Road, U-89, Storrs CT 06269; 2 Environmental Research Institute, University of Connecticut, 270 Middle Turnpike, Unit 5210, Storrs CT  06269 A lobster die-off reduced the 1999 fall landings in western Long Island Sound by more than 99%. The die-off corresponded in time with the application of pesticides for the control of mosquitoes that carried west Nile virus, a new emerging disease in North America. In order to determine the possible implication of pesticide application as a direct cause or contributing factor in the die-off, we studied the effects of experimental exposure to malathion on the health of lobsters in 20-gallon tanks. We determined the direct toxicity as well as sub-lethal effects on the immune system (cell counts and evaluation of phagocytosis using flow cytometry). The concentration of malathion that killed 50% of the animals (LC50) after a 96-hour exposure was determined as 33.5 µg/L upon single exposure. Malathion degraded rapidly in our system, with 65-77% lost after one day and 83-96% lost after three days. Malathion was not detected in lobster tissues at the end of the five-day exposure. Further, our results indicated that phagocytosis was significantly decreased three days after a single exposure to water concentration as low as 5.0 ppb (the lowest concentration tested), when measured water concentrations were as low as 0.55 ppb. Interestingly, those effects were not observed one and five days after exposure (although trends on day five were very similar to those on day three. Phagocytosis was also significantly affected in the course of the sub-acute (month long) exposure at 5, 21 and 46 ppb. Cell counts did not differ significantly upon exposure to malathion. Our data suggested that evaluation of phagocytosis using flow cytometry was a sensitive indicator of subtle sub-lethal effects of malathion, and that transient exposure to relatively small concentrations of malathion (6-7 times lower than the LC50) affected lobsters defense mechanisms, even with rapidly decreasing water concentrations. We plan to perform similar experiments to test the toxicity in lobsters of resmethrin and methoprene, two insecticides that were also used in the control of mosquitoes. Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page