Investiga??o da variabilidade gen?tica em bagres de interesse comercial e para conserva?

Abstract

Currently, studies of aspects of evolutionary biology in neotropical fishes diversity are still lacking, despite the strong environmental impact caused by human action that has had a negative effect in native species, many of which probably still unknown to science. The knowledge of genetic variability within and between populations is of utmost importance for planning of both fish breeding and conservation of natural populations. In the present study we have analyzed, especially through molecular cytogenetics techniques, 29 specimens of Pseudoplatystoma reticulatum (Paraguay river, state of Mato Grosso do Sul), 14 specimens of Pimelodus britskii (Igua?u river, state of Paran?), 6 specimens of Sorubim lima (Paraguay river, state of Mato Grosso do Sul) and 10 specimens of Steindachneridion parahybae (Para?ba do Sul river, state of S?o Paulo). Results indicate 2n = 56 chromosomes for all species, a distinct karyotype formula composed mainly of biarmed chromosomes. Other particular features were found, regarding the location for Ag+NORs and fluorescent in situ hybridization with 5S and 18S probes. Except P. britskii, which showed NORs in the terminal region of the long arm, all species showed Ag+NORs in the terminal position of the short arm. Another peculiar feature of this fish was the co-localization of one of the 5S and 18S rDNA sites, which could be considered an apomorphy to the others Pimelodidae studied. The present work aims to contribute to the collection of data on the cytogenetics studies of Siluriformes, considering that much of the here presented information are the first characterization of the karyotype macro-struture of analysed fishes.