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.
Three populations of the genus Crenicichla, namely Crenicichla iguassuensis, Crenicichla sp 1 and Crenicichla sp 2, from the Iguaçu River, were analyzed cytogenetically, and their nucleolus organizer regions, constitutive heterochromatin distribution and chromomycin A3 markings were studied. Karyotype analyses showed a diploid number of 48 chromosomes, made up of 2 metacentric pairs, 2 submetacentric pairs, 7 subtelocentric pairs, and 13 acrocentric pairs for the three Crenicichla species and no sexual chromosome differentiation.