Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaiba Lake, RS, Brazil.

The karyotypes of three species of fish of the Cichlidae family from the Forqueta river and several locations in Guaiba lake/RS (Brazil) were analyzed. All species presented 2n=48, while Gymnogeophagus gymnogenys showed two karyotypic formulae: 4m+44st-a with FN=52 and 6m+42st-a with FN=54. Gymnogeophagus labiatus presented 4m+4sm+40st-a and FN=56 and Geophagus brasiliensis 4sm+44st-a and FN=52. Simple NORs were found in all species with the exception of a population of G. gymnogenys from Saco da Alemoa/Barra do Ribeiro. CMA3 staining revealed NOR sites, while DAPI staining was negative and heterochromatin was limited to pericentromeric regions an d associated to NORs, except in G. labiatus. The data show a conserved pattern in Geophagus brasiliensis and karyotype variation in the species of Gymnogeophagus.