Intra-individual numerical chromosomal polymorphism in Trichomycterus davisi (Siluriformes, Trichomycteridae) from the Igua？u River basin in Brazil

cytogenetic analysis of trichomycterus davisi, collected from the igua？u river basin, has shown a diploid number of 2n = 54 chromosomes. however, we observed intra-individual numerical polymorphism in a t. davisi specimen. there were three cell populations with diploid number 2n = 54 (40m + 12sm + 2st), 2n = 55 (40m + 12sm + 2st + 1m) and 2n = 56 (40m + 12sm + 2st + 2a) chromosomes. this variation was attributed to a probable post-zygotic non-disjunction of a metacentric chromosome of small/middle size, followed by centric fission, which originated in this individual.