Multiple Nors in Bryconamericus aff. exodon (Osteichthyes, Characidae, Tetragonopterinae).

Fifteen examples of Bryconamericus aff. exodon from the Três Bocas stream in the basin of the Tibagi river (Parana, Brazil) were analyzed. They presented a diploid number of 52 chromosomes. Multiple NORS were detected by silver nitrate impregnation in the telomeric region on the short or long arm of different chromosomes, showing a variation from 2 to 5 NOR-bearing chromosomes. Treatment with chromomycin A3 (CMA3) showed regions rich in GC in different chromosomes, probably coincident with the AgNORS. In situ hybridization by fluorescence (FISH) with 18S rDNA probe showed 8 hybridization signs in the telomeric regions of the chromosomes, proving that this B. aff. exodon population has a greater number of ribosomal cistrons than were detected by Ag-banding.