The acute toxicity, genotoxicity, and cytotoxicity of the pirimicarb-containing commercial-formulation carbamate insecticide Aficida ® (50% pirimicarb) were evaluated on Cnesterodon decemmaculatus (Pisces, Poeciliidae) exposed under laboratory conditions. Micronucleus (MN) induction as well as alterations in the erythrocytes:erythroblasts ratios were employed as end-points for genotoxicity and cytotoxicity, respectively. Cr(VI) and cyclophosphamide were used as positive controls for the toxicity and geno-cytotoxicity assays, respectively. Mean values of 344.3 and 225.5mg Aficida ® /L were determined for LC-50 24h and LC-50 96h , respectively. In 48h-exposed fish, a MN increase was found in Aficida ® -treated fish in the 50–157mg/L concentration range. When fish were exposed to Aficida ® for 96h, only those animals treated at 50–100mg/L showed an increase in MN frequency. Cellular cytotoxicity, revealed by a decreased proportion of circulating erythrocytes and an enhancement of erythroblasts, was found after 48h of exposure in 50–157mg Aficida ® /L-treated fish, while, after 96h exposure, only 100–157mg Aficida ® /L induced the same effect. This species provides a useful experimental model for the biomonitoring of aquatic ecosystems.