Abstract
Astyanax fasciatus from Parapanema River basin was studied with respect to the karyotype structure, nucleolar organizer regions, 18S and 5S rRNA genes and C-banding pattern. The specimens presented 2n=46 chromosomes, with multiple NORs detected by silver nitrate staining (Ag-NORs) and confirmed by fluorescence in situ hybridization (FISH). Ten 18S rDNA sites were found, located in the telomeric regions of 4 distinct chromosome pairs, with bitelomeric locations in one of them. The 5S rDNA sites were detected in the interstitial regions of 4 chromosomes, 2 metacentric and 2 acrocentric ones. The C-positive heterochromatin was located in the telomeric regions of some submetacentric, subtelocentric and acrocentric chromosomes. Variations in the karyotypic structure, C-positive heterochromatin pattern and location 18S rDNA sites are discussed.
