Mapping 45S and 5S ribosomal genes in chromosomes of Anostomidae fish species (Ostariophysi, Characiformes) from different Amazonian water types

The fish from the family Anostomidaerepresent one of the most important groups of freshwater ichthyofauna from South America, with species of high economical value. The migratory characteristic of some species, through the several Amazonianenvironments, takes them into waters with different physico-chemical characteristics. Cytogenetic studies on the Anostomidaedemonstrate that these fishes have a conserved diploid number and karyotypemacrostructure. So, to verify if this conservation occurs also in the genomic level, the current study aimed at a chromosomal comparative physical mapping, using 45S and 5S rDNA, of seven species of anostomids: Leporinus fasciatus, L. agassizi, L. friderici, L. trifasciatus, Rhytiodusmacrolepis, Laemolytataeniata, and Schizodon fasciatus, collected in different Amazonianenvironments. The results obtained corroborate the conservation of the karyotypemacrostructure. However, significant differences were found in the distribution of heterochromatinand on the pair bearing the nucleolus organizer region. The staining of 45S and 5S rDNA by FISH highlighted, for four of the seven species, more than one chromosome pairbearing the site 45S. The 5S rDNA, although present in only one chromosome pair, varied in its chromosome and karyotypeposition. Thus, although the Anostomidaefamily has a conserved chromosomic macrostructure the use of molecular techniques revealed the presence of chromosomic translocationduring the evolution of these fishes.