Comet assay and micronucleus test in circulating erythrocytes of Aequidens tetramerus exposed to methylmercury.

BACKGROUND: Comet assay and micronucleus test have been used increasingly to evaluate the genotoxicity of many metals and their organic compounds in aquatic ecosystems. The use of endemic aquatic organisms as biological sentinels has proved useful in environmental monitoring. In this study, the genetic damage caused by methylmercury (MeHg) in Aequidens tetramerus (commonly called acará-sela) was assessed using the comet assay and by testing for micronucleus and other nuclear abnormalities. MATERIALS AND METHODS: Specimens were acclimatized in individual aquariums to laboratory conditions and then exposed to 2 mg l(-1)MeHg. Peripheral blood samples were obtained from specimens of A. tetramerus and subjected to the comet and micronucleus assays. RESULTS: The comet assay showed a significant increase of tailed nucleoids in the erythrocytes of fish treated with MeHg (p<0.0001). Our results in the micronucleus test also indicated that MeHg is potentially mutagenic (p<0.003), with more nuclear morphological alterations than typical micronuclei. CONCLUSION: The combination of both assays - comet and micronucleus - is adequate and advantageous for genotoxicity evaluation. The level of damage detected by comet assay was higher than that found in the micronucleus test and the damage index increased with a longer exposure of fish to this xenobiotic; such damage is often not inherited by future cellular generations and, for this reason, cannot be detected by the micronucleus assay. Our results also demonstrated that A. tetramerus is an adequate model for biological studies that evaluate genotoxic effects in aquatic environments.