B chromosome polymorphism in the fish, Astyanax scabripinnis.

Four populations of Astyanax scabripinnis (Pisces, Characidae) were analyzed for B chromosome features. This species contains a metacentric macrochromosome (BM), similar in size to the first chromosome of the karyotype, besides two variant forms, a large submetacentric (BSM) and a small metacentric (Bm), both showing a reduced frequency. These variant forms were observed only in the populations from the Campos do Jordão region (São Paulo State, Brazil), although not present in all the populations sampled.