The ecotoxicological impact of the carbamate insecticide cartap (1,3 di (carbamoythio)-2-dimethyloaminopropan) used for agriculture pests and as mollusquicide of vectors of Public Health importance was evaluated, on two fish species ofthe continental aquatic ecosystem. Poecilia reticulata (Peters 1859) "guppy" (Poecilidae) and Paracheirodon innesi (Myers 1936) "Neon Tetra" (Characidae) were employed as non-target organisms in assays of short duration to determine the toxicological impact of cartap. For both fish, percentage of mortality and two sublethal responses: increase of opercula movement and strange swim, were evaluated. In P. reticulata after 3 h exposure it was found a LC50 (mean Lethal Concentration) of 6.75 mg' · L-1 and values Of EC50 (mean Effective Concentration) of <7.55 and <8.16 mg·L-1 as speed up of opercula movement and strange swim, respectively. For P. innesi, it was found an LC50 value of <0.02 mg-1 and values of EC50 of <0.0.1 and <0.03 m.g·L-1, as speed up of opercula movement and strange swim, respectively. P. innesi was more sensitive to cartap than P. reticulata. Risk Quotients (RQ) to evaluate environmental risk (ERA) of this insecticide on aquatic ecosystem were calculated, indicating that P. innesi was more accurate than P. reticulata as ecotoxicological tool to evaluate cartap.