Almost all species of the Curimatidae family have a stable karyotype, with a diploid number of 54 metacentric (M) and submetacentric (SM) chromosomes, and one sole nucleolus organizer pair. This family has considerable specific diversity in Argentinean fluvial basins; however, no cytogenetic data are available. Eight species from the Paraná River (Argentina): Cyphocharax voga, C. spilotus, C. platanus, Steindachnerina brevipinna, S. conspersa, Curimatella dorsalis, Psectrogaster curviventris, and Potamorhina squamoralevis were analyzed cytogenetically. Chromosome preparations were obtained from direct samples and through cell culture, and they were processed for conventional, C- and nucleolar organizer region-banding. Six of the species exhibited the standard family karyotype, with 2n = 54 M-SM and fundamental number of chromosomes (FN) = 108, as well as variations in the chromosome formula, and in heterochromatic and nucleolar organizer regions. Though nucleolar organizer regions were located on only one chromosome pair, they varied in both carrier chromosomes and pairs involved. On the other hand, C. platanus showed a complement of 2n = 58 M-SM and subtelocentric with FN = 116, and P. squamoralevis presented 2n = 102, with some M-SM and a large number of acrocentric chromosomes. Even though the karyotype macrostructure appears to be conserved, the speciation process within the family has been accompanied by micro-structural rearrangements, as evidenced by pattern diversity in the heterochromatin and nucleolar organizer regions. Some changes in chromosome macrostructure have also occurred in this group, primarily in C. platanus and P. squamoralevis, in which there have been centric dissociations and inversions.
Key words: Paraná River, Curimatidae, Nucleolar organizer regions, Cytogenetic studies.