Cytogenetical analyses in three fish species of the genus Pimelodus(Siluriformes: Pimelodidae) from rio S？o Francisco: considerations about the karyotypical evolution in the genus

karyotypes and other chromosomal markers were investigated in three species of the catfish genus pimelodus, namely p. fur, p. maculatus and pimelodus sp., from municipality of três marias, minas gerais, brazil, using differential staining techniques (c-banding, silver nitrate and cma3 staining). the diploid chromosome number was 2n = 56 in p. maculatus and pimelodus sp., while in p. fur 2n = 54. the karyotype of p. fur consisted in 32m + 8sm + 6st + 8a with fundamental number (nf) of 100, that of p. maculatus 32m + 12sm + 12a with nf = 112, and that of pimelodus sp. had 32m + 12sm + 6st + 6a with nf = 106.the nucleolar organizer regions (nors) in all three species were invariably detected in telomeres of longer arm of the 20th chromosome pair. these sites were also positive after cma3 and c-banding. no heteromorphic sex chromosomes were detected and c-banding pattern was species specific. inferences about the karyotype differentiation in pimelodus and putative chromosomal rearrangements are hypohesized.