Karyotype Analysis and Mapping of the 18S and 5S Ribosomal Genes in Astyanax fasciatus (Teleostei, Characiformes) from Paranapanema River Basin

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.