ABSTRACT
In the present work, morphometric and cytogenetic analyses were carried out in populations of the fish Astyanax fasciatus (Characidae) from Contas and Recôncavo Sul River basins (State of Bahia, Brazil), providing new data on the genetic structure of this species along the region. Based on morphologic measurements, we observed that populations from the same hydrographic basin were more similar to each other (Contas and Preto do Costa Rivers), and remarkably divergent from Recôncavo Sul (Mineiro Stream), as indicated by clustering analysis. Cytogenetic data revealed a same diploid number for all populations (2n = 48), but distinct karyotype formulae (8M+24SM+12ST+4A, FN = 92 in Contas River, 8M+24SM+10ST+6A, FN = 90 in Preto do Costa River, and 8M+18SM+16ST+6A, FN = 90 in Mineiro Stream). Ag-NORs were identified at telomeres on a subtelocentric chromosome pair, although multiple ribosomal sites have been detected in some specimens from Contas River. These results show that A. fasciatus populations from northeastern river basins are well differentiated and present peculiar cytogenetic features when compared to populations from other regions. Therefore, the apparent chromosomal plasticity of this species, likely to represent a complex of cryptic forms, is corroborated. Finally, we demonstrated that morphological features can be successfully used to support other sources of genetic information.