The frequencies of micronuclei (MN) and morphological nuclear abnormalities (NA) in erythrocytes in the peripheral blood of tambaqui (Colossoma macropomum), treated with 2 mg.L-1 methylmercury (MeHg), were analyzed. Two groups (nine specimens in each) were exposed to MeHg for different periods (group A - 24 h; group B - 120 h). A third group served as negative control (group C, untreated; n = 9). Although, when compared to the control group there were no significant differences in MN frequency in the treated groups, for NA, the differences between the frequencies of group B (treated for 120 h) and the control group were extremely significant (p < 0.02), thus demonstrating the potentially adverse effects of MeHg on C. macropomum erythrocytes after prolonged exposure.

Micronucleus (MN) assay has been extensively used in the evaluation of DNA damage. Mutagenesis and genotoxicity studies employed this methodology to evaluate possible genotoxic risk due to exposition to hazardous xenobiotics in different organisms, including aquatic sentinel organisms. MN assay in such species is sensitive, fast, and an important biomarker of mutagenic exposure in the environment. The use of bioassays, considering the toxic effects of isolated or combined contaminants, is also important since the environmental variants are minimized. The aim of this study is to gather and evaluate published data on the use of fish MN assay in biomonitoring and genotoxicity assays. In addition, we show the results of both micronuclei and other nuclear abnormalities in erythrocytes from Colossoma macropomum, exposed to methylmercury. Specimens (n = 9) were subjected to 2 mg/L of methylmercury, with an equal control group. Chi-square test was performed to compare the frequencies of nuclear abnormalities between control and treatment groups. The contingence table of χ2 test showed a significant increase of altered cells in the exposed group. Our results support the importance of MN test as an effective indicator for genotoxicity in fishes, which can be used with exposition bioindicators of human populations exposed to chemical pollutants of consuming water.

This study gathered the largest amount of evidence available concerning the presence of helminths in the Hoplias malabaricus species (Trahira, traíra in Portuguese) from limnic ecosystems in South America. At least 18 species of helminths belonging to 15 genera, 14 families, 10 orders, and 8 classes were found. The greatest diversity of parasitic species was observed among the Digeneans and acanthocephalus. Throughout the text, helminths are presented in four sections corresponding to their phyla: Platyhelminthes, Acanthocephala, Nematoda, and Annelida. The different niches occupied by the Trahira in the heteroxenic helminth cycles are also analyzed, verifying whether this fish acts as an intermediate or a definitive host.