Parasitoses in fi sh farming are treated by the application of pesticides formulations commonly used in agriculture or veterinary medicine. For the control of ectoparasites, that cause economic losses to the fi sh production Difl ubenzuron is utilized by direct application into water at a 2 mg.L -1 concentration. However, this practice can intoxicate nontarget species. This research aimed at determining the acute toxicity of difl ubenzuron to Daphnia magna, Poecilia reticulata and Lemna minor; evaluating its environmental risk and defi ning the role of the sediment in the bioavailability of this insecticide in the water. Results of the study implicate difl ubenzuron as being extremely toxic to D. magna. However, no signifi cant toxicity was observed in P. reticulata and L. minor. Bioavailability of this insecticide was signifi cantly reduced by the presence of sediment in the water.