Análise cariotípica de Pimelodus blochii (Valenciennes, 184), (Siluriformes, Pimelodidae) do rio Tapajós e Baixo Amazonas

Abstract

The genus Pimelodus encompasses 33 species distributed endemically in the Neotropical region occurring in the Araguaia, Tocantins, Amazonas, Paraná and Orinoco basins. In the present study we analyzed the karyotype of Pimelodus blochii from the Tapajós and lower Amazonas Rivers. Were analyzed 11 specimens and the karyotype was studied with conventional giemsa staining, C banding, Ag-NOR, Chromomycin A3 and FISH of DNAr18S and 5S probes. The results showed variation in the diploid number (2n=58 and 2n=56). Samples from Itaituba, Tapajos river have diplóide number of 2n=56 chromosomes, while samples from Santarém, Almeirim and Oriximiná have 2n=58. The nucleolar organizing regions were detected on the short arm of an acrocentric pair, with similar position of the positive CMA3 sites, and the localization of DNAr18S probes. The sites DNAr18S and 5S were co-localized in a chromosomal pair. The results evidenced karyotipic divergence between P. blochii population from the Tapajós River and lower Amazonas, what is interpreted in support to hypothesis of P. blochii species complex.