Summary Among the Perciformes, Cichlidae represent the more specious group, geographically distributed in Africa, Asia and America. In the present work, 7 species of 5 genera of cichlids from the Paraná River (Misiones, Argentina) were cytogenetically characterized and discussed some aspects of the chromosome evolution. The following chromosome numbers and formulaes: were found for each analyzed species: Crenicichla niederleinii 2nϭ48 ( In B. vittata the microchromosomes are not heterochromatic and the 5th pair shows short arms entirely stained and, in coincidence, the AgNORs appears located at the same region. The results obtained evidence a wide chromosomal variation, either in number and structure that could be integrated with morphological and molecular data in phylogenetic studies.

ABSTRACT. The Potamotrygonidae family represents the only freshwater group of specialized elasmobranchs and is composed of 4 genera: Plesiotrygon, Paratrygon, Potamotrygon, and Heliotrygon. Individuals of Potamotrygon motoro were collected from the Paraná River at Ituzaingó (Province of Corrientes) in Argentina. Mitotic preparations were obtained using direct techniques and lymphocyte cultures. Chromosomes were studied with conventional Giemsa, C-band and nucleolus organizer region stainings. The diploid number and karyotype formulae were 2n = 66 with 33 homomorphic pairs (14M + 16SM + 22ST + 14A) in females and 2n = 65 with 31 homomorphic pairs plus 3 heteromorphic chromosomes (13M + 15SM + 23ST + 14A) in males. Heterochromatin was distributed at ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 12 (3): 2368-2375 (2013) Sexual chromosome system in Potamotrygon motoro 2369 the pericentromeric regions of almost all chromosomes and in the telomeric and interstitial positions of some chromosomes. nucleolus organizer regions were multiple and located at telomeric regions. Because of the clear karyotype differences between the 2 sexes and the presence of 3 unpaired chromosomes in males, it is possible to suggest the occurrence of a multiple sex chromosome system, with male heterogamety (X 1 X 1 X 2 X 2 /X 1 X 2 Y). Further cytogenetic studies are required to develop a hypothesis about the origin of the multiple sex chromosome system in P. motoro.

Karyotypic studies on a population of Apareiodon affinis from Paraná river (Argentina) were carried out. Although the modal diploid number of the population was 54 chromosomes, some structural and numerical polymorphisms were detected. In the first case these variations deal with the number of mono-and biarmed chromosomes and in the second with the presence of an additional unpaired chromosome that appeared only in female individuals, suggesting some kind of linkage with a chromosomal system of sex determination. These data were compared with the available cytogenetic information and the geographic distribution of A. affinis.

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