Short communication Molecular cytogenetics of Salminus fish (Characiformes) based on 5S and 18S rRNA genes hybridization, fluorochrome staining and C-banding Issakar Lima Souza a, * , Ludier Kesser Santos-Silva a , Paulo Ce ´sar Venere a , Orlando Moreira-Filho b a Departamento de Cie ˆncias Biolo ´gicas e da Sau ´de, Instituto Universita ´rio do Araguaia, Universidade Federal de Mato Grosso, Rodovia MT 100, km 3.5, CEP 78698-000, Pontal do Araguaia MT, Brazil b Departamento de Gene ´tica e Evoluc ¸a ˜o, Universidade Federal de Sa ˜o Carlos, Rodovia Washington Luı ´s (SP 310), Km 235, CEP 13565-905, Sa ˜o Carlos SP, Brazil Received 23 July 2007; received in revised form 24 September 2007; accepted 25 September 2007 Abstract Karyotype, mapping of nucleolar and 5S rRNA genes and distribution of constitutive heterochromatin supposedly AT-rich were characterized on two isolate populations of Salminus brasiliensis, the biggest characid fish, and three population of Salminus hilarii. The diploid number 2n = 50 and the karyotype formulae (10M + 20SM + 20ST/A) were the same to Salminus species studied. The position of 18S rDNA cluster identified by FISH coincidewith chromomycin A 3 labeling (CMA + ) in the long arm telomeric portion of sixth pair. Subtle differences for the disposal of the 5S rRNA gene in the chromosome of the Salminus are presented. The distribution of the constitutive heterochromatins and DA/DAPI + bands are described. # 2007 Elsevier Ltd. All rights reserved. Keywords: Salminus; Chromomycin A 3 ; Constitutive heterochromatin; DA/DAPI 1. Introduction The species of the genus Salminus are neotropical benthopelagic and potamodromous fishes composed by Salminus affinis (Steindachner, 1880), Salminus brasiliensis (Cuvier, 1817) and Salminus hilarii (Valenciennes, 1840). They are migratory and feed on fish and crustaceans. Systematic review allocated this genus for Incertae sedis in Characidae (Characiformes) (Lima et al., 2003). The S. brasiliensis, a jaw characin or regionally termed ‘‘dourado’’ (gold fish), the biggest characid fish, inhabit the great rivers from Parana ´-Paraguay and Sa ˜o Francisco basins. Adults reach more than 20 kg and are very important on commercial fishery and regional culinary in Brazil. This species is very desirable on sport fishing because it presents a great resistance to the capture, jumping several times more than one meter from water surface when baited. Nevertheless, this species is cited in a list of fishes that are vulnerable to change of habitats (Agostinho et al., 1997), therefore are related in the Livro Vermelho da Fauna Ameac ¸ada do Estado do Parana ´ (translation: red book of endangered fauna of the Parana ´ State). The S. hilarii, regionally termed ‘‘tabarana’’ or ‘‘saicanga’’, is smaller than S. brasiliensis and shows a marked red caudal fin and a body surface with a silver brightness. They occur in the Parana ´-Paraguay, Sa ˜o Francisco, Amazonas and Araguaia- Tocantins basins. Also are listed in the Livro Vermelho da Fauna Ameac ¸ada do Estado do Parana ´(IAP, 2007). Despite your great commercial, ecological and cultural importance, the only one cytogenetic study in this group was performed by Marco (1986, unpublished data). In the present paper are described the karyotypes, distribution of the constitutive heterochromatins, use of fluorochrome stains, nucleolar (18S) and 5S rDNAs location, to S. brasiliensis and S. hilarii chromosomes sampled from different Brazilian basins. 2. Materials and methods Cytogenetic analyses were performed in specimens of S. brasiliensis from two rivers of different Brazilian basins: 29 specimens from Mogi-Guac ¸u (municipality of Pirassununga SP, www.elsevier.com/locate/micron Available online at www.sciencedirect.com Micron 39 (2008) 1036–1041 * Corresponding author. Tel.: +55 66 3402 1126; fax: +55 66 3402 1110. E-mail address: issakar@pq.cnpq.br (I.L. Souza). 0968-4328/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2007.09.007