Karyotypic Study of Three Species of Pimelodus (Pisces, Pimelodidae) from the Paraguai River Basin

The present study involved the karyotypic analysis of Pimelodus argenteus, P. mysteriosus and P. maculatus, from the the Paraguai River, in the municipality of Corumbá-MS/Brazil. All the species had a diploid number of 56 chromosomes with differences in the karyotypic formulae. In P. argenteus, there was a secondary constriction, quite conspicuous in one of the homologous chromosomes. NOR staining was observed on one pair of ST chromosomes at the terminal position in the three species, in which it was localized on short arm in P. argenteus and P. mysteriosus and on long arm in P. maculatus. In P. argenteus and P. mysteriosus, C-banding showed heterochromatin distributed homogeneously in various chromosomes of the complement, mainly in telomeric regions. In P. maculatus, heterochromatic staining was found to be very evident in one pair chromosomes with strong interstitial staining. The fluorochrome CMA3 stained in P. argenteus and P. mysteriosus only the NOR-bearing pair of chromosomes. In P. maculatus, fluorescent staining was observed in various chromosomes in addition to the NOR pair, including one pair with interstitial staining. Treatment with BC+CMA3 produced in P. argenteus and P. mysteriosus a much more fluorescent staining of the pair of NOR-bearing chromosomes, mainly in P. argenteus, along with weak staining of other chromosomes. In P. maculatus, fluorescent staining was much brighter after this treatment.