Nucleolar Organizing Regions in Some Species of Neotropical Cichlid Fish (Pisces, Perciformes)

SUMMARYIn the present study, 10 neotropical species of family Cichlidae (Pisces, Perciformes) were submitted to analysis of the nucleolar organizing regions (NORs). In 8 of these species, the NORs were located in the first pair in the complement and coincided with the secondary constrictions observed there, whereas in Cichlasoma facetum and Geophagus brasiliensis the NORs were located in another chromosome pair. The possibility that the predominant location of NORs in the 1st pair in the karyotype indicates a more primitive condition of this group of fish is discussed. Variations in NOR size between homologous chromosomes of some species were also observed.