Cytogenetic characterization of Hypostomus nigromaculatus (Siluriformes: Loricariidae)

Hypostomus is the most speciose genus in the family Loricariidae, with approximately 120 species. These fish show a wide morphological and color variation, which hinders the identification of species, mainly of widely distributed representatives. The aim of this study was to contribute to the current knowledge on cytogenetic features of Hypostomus nigromaculatus. Three specimens of H. nigromaculatus, collected in two tributaries of rio Tibagi, Paraná, and in Cachoeira de Emas, rio Mogi-Guaçu, São Paulo, the latter being the type locality of H. nigromaculatus, were studied. Chromosomal preparations were submitted to Giemsa staining, silver nitrate impregnation, C-banding and CMA3 and DAPI fluorochromes staining. All samples presented 2n = 76, but the rio Mogi-Guaçu sample differed from those from tributaries of rio Tibagi in relation to karyotype formulae, distribution and composition of heterochromatin, and NOR location. The silver nitrate staining revealed the presence of multiple Ag-NORs for all samples, but with differences on the location on chromosomes. CMA3 staining reveled bright signals equivalent to NOR-bearing chromosomal segments; such sites were characterized by negative, i.e. unstained, marks after DAPI staining. The pattern of heterochromatin distribution was distinctive among samples from rio Mogi-Guaçu and tributaries of rio Tibagi. The differences observed between the sample from rio Mogi-Guaçu and the ones from tributaries of rio Tibagi allow us to suggest that these samples are presently isolated. Further analyses are necessary to ascertain whether such isolation refers to distinct populations or characterizes true different species. O gênero Hypostomus é um dos mais especiosos na família Loricariidae, tendo aproximadamente 120 espécies. Apresenta uma ampla diversidade quanto ao padrão de coloração e morfologia, o que dificulta a identificação de determinadas espécies, principalmente aquelas com ampla distribuição geográfica. Para isso os dados obtidos neste trabalho contribuem para os estudos citogenéticos de Hypostomus nigromaculatus. Foram analisados três exemplares de H. nigromaculatus de afluentes do rio Tibagi, Paraná e Cachoeira de Emas, rio Mogi-Guaçu, São Paulo, sendo esta última, a localidade tipo de H. nigromaculatus. Os cromossomos foram submetidos à coloração convencional (Giemsa), impregnação por nitrato de prata, bandamento-C e coloração com os fluorocromos CMA3 e DAPI. Todos os exemplares apresentaram 2n = 76, no entanto