In Pimelodidae fish the available chromosome numbers range from 2nϭ46 to 2nϭ63, the value 2nϭ56 being the most frequent one. In the present paper 6 species belonging to the Rhamdiinae subfamily were analyzed: Rhamdia hilarii, R. quelen, Cetopsorhamdia sp., C. iheringhi, Imparfinis cf. piperatus and Imparfinis aff. schubarti. Chromosome preparations were obtained by direct and short term culture methods from kidney cells and analysed under standard Giemsa staining, C-banding and NOR silver

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... ng. Rhamdia species present a basic karyotype composed by 58 chromosomes and the NORs are located on the short arm of a subtelocentric chromosome pair. Cetopsorhamdia sp., C. iheringhi and Imparfinis aff. schubarti. also shows 2nϭ58, while I. cf. piperatus is the only analyzed species presenting 2nϭ56. However, these 4 species show an interstitial NOR location. These chromosomal data agree with the occurrence of subgroups in the Rhamdiinae subfamily, proposed on the basis of their morphological traits.