Cytogenetic characterization of species of the family Heptapteridae (Teleostei: Siluriformes) from the Cuiabá and Ivaí River Basins, Brazil.

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-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 A3 (CMA3) 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 CMA3 were detected in the first pair, but negative signals were detected for DAPI staining. These results con-tribute to the karyotypic description of the less-studied species in the Brazilian Midwest.

Cytogenetic description of Ancistrus abilhoai (Siluriformes: Loricariidae) from Iguaçu River basin, southern Brazil.

The Iguaçu River basin is a tributary to the upper Paraná River in southern Brazil, and is considered an important aquatic ecoregion that, although having few species of fish, 51-71% of these are apparently endemic. Ancistrus abilhoai is one of three recently described species for this basin and is currently considered endemic to the basin. In this study, we present the chromosomal structure of two populations of Ancistrus abilhoai one collected in the Iguaçu River, in Paraná State, and another collected in the Timbó River, a tributary of the Iguaçu River, in the State of Santa Catarina. Karyotype analyzes were performed in 11 specimens from the Iguaçu River (four females and seven males) and 12 specimens (all males) from Timbó River, revealing 2n = 48 chromosomes with a karyotype formula of 22m + 14sm + 6st + 6a in both populations. Analysis of active nucleolar organizer regions (Ag-NORs) and fluorescent in situ hybridization (FISH) with 18S rDNA probes revealed the submetacentric pair 13 bearing marks at terminal positions on the short arms. Considered as plesiomorphic chromosomal markers in Loricariidae, asynteny 18S and 5S rDNA, and small amounts of heterochromatin were observed. In this study, the first chromosomal data of A. abilhoai are presented with comments on karyotypic characteristics of the genus.