Karyotypic studies were carried out on three species of the genus Oligosarcus: O. paranensis, O. pintoi, and O. longisrostris. All of them showed a diploid number of 50 chromosomes and the same karyotypic formulae (4M + 10SM + 16ST + 20A). Silver nitrate staining revealed single NORs in O. longirostris and multiple NORs in O. paranensis and O. pintoi. Heterochromatin seemed to play an important role in the chromosomal diversification of these species. Based on cytogenetical data, speciation hypotheses within this group were proposed, reinforcing the importance of chromosomal studies for a better understanding of evolution within the genus Oligosarcus, as well as within the family Characidae.
Cytogenetic studies; Oligosarcus; Acestrorhynchinae; chromosome banding
