COMPARATIVE CYTOGENETIC STUDY AMONG THREE FISH SPECIES: AN ANALYSIS FROM A WATER DIVIDE REGION ESTUDO CITOGENÉTICO COMPARATIVO EM TRÊS ESPÉCIES DE PEIXES: UMA ANÁLISE DE UMA REGIÃO DE DIVISOR DE ÁGUAS

The aim of the present study was to characterize chromosomal differences between two populations separated in the past for a water divide. Processes of differentiation have been identifi ed in the species studied, being justifi ed by the separation of streams from past for a water divide. Karyotypic data were presented for Astyanax altiparanae, Geophagus brasiliensis and Gymnotus carapo populations of two different river systems of the upper Parana: ribeirao do Pântano (Tiete basin) and ribeirao do Feijao (Mogi Guacu basin) in the Sao Carlos region, state of Sao Paulo. The Astyanax altiparanae, presented a diploid number of 2n=50 chromosomes. The Geophagus brasiliensis diploid numbers was 2n=48 chromosomes and Gymnotus carapo a diploid number of 2n=54 chromosomes. An analysis was made of constitutive heterochromatin by C-banding, detection of nucleolar organizer regions and the technique of Hybridization in situ Fluorescent with probes 18S rDNA and 5S rDNA. These results indicate that the species analysed showed differences of karyotype, showing that each population follows its own evolution, as a result of a restrictive process of gene fl ow.