Abstract
Astyanax ribeirae is a characin fish endemic to Ribeira de Iguape river basin, Brazil. Karyotypic analysis of the specimen from distinct geographic regions depicted similar karyotypic features, i.e. 2n = 50 constituting the 4 M + 10SM + 6ST + 30A and a fundamental number (FN) equal to 70. Further analysis on linear differentiation using silver nitrate staining, c-banding and rDNA localization revealed single NOR on ST/A chromosomes, heterochromatin blocks in the pericentromeric region of some chromosomes, and four 18S rDNA sites and six 5S rDNA sites, all located on ST/A chromosomes. FISH with As-51 satellite DNA probe presented no homology signals in chromosomes of A. ribeirae, indicating uniqueness of species within the genus Astyanax. The chromosomal and molecular cytogenetic data obtained on A. ribeirae specimens collected from Atlantic rainforest areas are discussed to elucidate relationship between this species and other species in the genus vis-a-vis chromosomal evolution of the group. This is the first report on cytogenetic analysis of Astyanax ribeirae.
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