Ecotoxicological tools for the tropics: Sublethal assays with fish to evaluate edge-of-field pesticide runoff toxicity.

This study proposes short-term sublethal assays for the tropics using the fish Poecilia reticulata. Assays were evaluated under realistic exposure scenarios by simulating a runoff over an agricultural area sprayed with deltamethrin (Decis). In situ assays were performed inside microcosms set up to simulate runoff water entrance in lentic systems. Laboratory assays were conducted with water samples from the microcosms. In both assays the biochemical parameters were similarly responsive to Decis, with a significant inhibition of acetylcholinesterase (30-46%) and induction of lactate dehydrogenase (33-67%) and glutathione S-transferases (48-176%) activities, observed as of the lowest Decis dose. Postexposure feeding was more sensitive in the laboratory assay than in situ. Among the additional potential stressors, only acetylcholinesterase was significantly influenced by the runoff per se. The proposed methodologies were well adapted for assays with P. reticulata, as organisms were easily deployed and retrieved and enzymatic activities and postexposure feeding were sensitive endpoints.