Abstract
The genus Astyanax, one of the largest genera in the family Characidae, comprises a large number of similarly shaped fish species. In this study, the karyotypes of three sympatric species of Astyanax were analyzed. Astyanax asuncionensis showed a karyotype of 2n=50 chromosomes (14M+26SM+10ST/A). Astyanax lineatus also had 2n=50 chromosomes, but its karyotype was different (8M+24SM+18ST/A). Astyanax marionae showed a karyotype of 2n=48 chromosomes (8M+24SM+16ST/A). Ag-NORs appeared in two pairs of chromosomes in Astyanax marionae and in only one pair in the other two species. The variation in the karyotype formula and number of nucleolar organizer regions highlights the importance of these markers in distinguishing among similarly shaped species.
