ABSTRACT. We cytogenetically characterized three species of Heptapteridae (Pimelodella sp, Pimelodella taenioptera, and Imparfinis schubarti) by investigating the distribution of constitutive heterochromatin and nucleolar organizer regions by silver nitrate impregnation (Ag-NOR) and fluorescence in situ hybridization. Pimelodella sp showed had a diploid number (2n) = 46 chromosomes, 26m + 10sm + 10st, and FN = 92; P. taenioptera, 2n = 52 chromosomes, 26m + 22sm + 4st, and FN = 104; and I. schubarti, 2n = 58 chromosomes, 28m + 28sm + 2st, and FN = 116. The two Pimelodella species had Ag-NORs sites on the submetacentric pair 14, located on the short arm in terminal position. In I. schubarti, the Ag-NORs sites were in an interstitial position on the long arm of the metacentric pair 1. C-banding revealed that Pimelodella sp contained a small amount of constitutive heterochroma- Cytogenetics of species of the family Heptapteridae tin, whereas P. taenioptera contained a higher number of heterochromatic regions, in the pericentromeric, interstitial, and telomeric positions. I. schubarti had markers in centromeric and telomeric regions of a few chromosomes, and a large pericentromeric block on pair 1. Fluorochrome chromomycin A 3 (CMA 3 ) staining revealed positive signals on pair 14 in both Pimelodella species. Treatment with 4ꞌ,6-diamidino-2-phenylindole (DAPI) revealed no markings in P. taenioptera, but an interstitial marking on the long arm of pair 14 in Pimelodella sp. In I. schubarti, positive signals of CMA 3 were detected in the first pair, but negative signals were detected for DAPI staining. These results contribute to the karyotypic description of the less-studied species in the Brazilian Midwest.

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