Cytogenetic characterization of Rhamdia
quelen (Siluriformes, Heptapteridae) from the Bodoquena Plateau, Mato Grosso do Sul, Brazil

V.P.O. Moraes¹, S.S. Cereali², O. Froehlich² and A.L. Dias^1
1Departamento de Biologia Geral, Universidade Estadual de Londrina, CCB, Londrina, PR, Brasil
²Departamento de Biologia, Universidade Federal do Mato Grosso do Sul, CCBS, Campo Grande, MS, Brasil
Corresponding author: A.L. Dias
E-mail: [email protected]

Genet. Mol. Res. 6 (3): 627-633 (2007)
Received May 17, 2007
Accepted August 15, 2007
Published September 30, 2007

ABSTRACT. We made a cytogenetic study of the fish Rhamdia quelen collected from the Bodoquena Plateau, an isolated national park region in Mato Grosso do Sul State, Brazil. The diploid number was 2n = 58, with 36 metacentric + 16 submetacentric + 6 subtelocentric chromosomes. We found one to three B chromosomes, which were metacentric and submetacentric and of medium size, showing both intra- and interindividual variation. The nucleolus organizer region (NOR) was located in the terminal region of the short arm of submetacentric pair 20. Staining with CMA₃ fluorochrome revealed the NOR location, while there was no evidence of fluorescent staining with DAPI. C banding revealed heterochromatin mainly in the terminal regions of the chromosome arms, including the NOR pair. In addition, metacentric pair 2 showed three heterochromatic blocks in the terminal portions and in the pericentromeric region. The B chromosomes appeared euchromatic. The CB + CMA₃ staining combination demonstrated only one chromosome pair with fluorescence, probably the NOR-bearing one, while CB + DAPI gave various fluorescent signals, including metacentric pair 2, indicating that these heterochromatic regions are AT-rich in this population of R. quelen. The R. quelen population in this isolated region of Brazil is chromosomally distinct from that of other populations that have been studied.

Key words: B chromosomes, C banding, Ag-NOR, Chromomycin A₃, DAPI