Five new species of the Neotropical characiform genus Astyanax Baird & Girard are described from Rio Iguaçu at the border of Paraná and Santa Catarina states, southeastern Brazil and Astyanax gymnogenis Eigenmann is redescribed. Each new species can be distinguished from all other Astyanax species from the upper Rio Paraná basin by exclusive combinations of: tooth shape, number of dental cuspids, distance between third infraorbital and preopercle, number of lateral line scales, longitudinal series of scales, number of gill-rakers and differences from shape of body and head traits. This study proposes the species of genus Astyanax from Rio Iguaçu as probably endemic, since all of them are absent from tributaries of the Rio Paraná hydrographic system. The high degree of diversification acquired by those Astyanax species in the Iguaçu basin may perhaps be allied to the long isolation period of this river from the Rio Paraná basin caused by the Iguaçu waterfalls. This barrier probably isolated those basins resulting in original groups of Characiformes and then Astyanax species, both isolated from one another and both different from their relatives in neighbouring basins.
freshwaterfishes; Ostariophysi; taxonomy; Characidae; Astyanax; neotropics
