Daphnia magna feeding behavior after exposure to tetradifon and recovery from intoxication

The feeding behavior of the cladocera Daphnia magna subjected to a short-te rm exposure to the acaricide tetradifon (4-chlorophenyl 2,4,5-trichlorophen yl sulfone) was studied. The experiments were performed using the unicellul ar algae Nannochloris oculata at a density of 5x10(5) cells/ml as food for the organisms. In a first experiment, three generations (F0, F1, and F3) of the daphnids were exposed to sublethal levels of tetradifon (0.1, 0.18, 0. 22, and 0.44 mg/l) and the effect of the toxicant on filtration and ingesti on rates was determined. Rates of filtration and ingestion of D. magna decl ined in the three generations studied Kith increasing toxicant concentratio ns; however, toxicant effect was greater in daphnids from generations F1 an d F3 than in those from the parental generation F0. A second experiment was conducted in order to evaluate whether animals of a first (1) or third (F3 ) generation coming from parental daphnids (F0) previously exposed to those pesticide concentrations exhibited any alteration in feeding behavior when transferred to clean,vater (recovery period). The results indicated that t he feeding rates of D. magna generations F1 and F3 were still affected duri ng the recovery period but to a less degree. The effective tetradifon conce ntrations D. magna at which feeding rates were reduced to 50% that of contr ols (EC50) were also calculated. (C) 1999 Academic Press.