Gene mapping of 5S rDNA sites in eight fish species from the Paraíba do Sul river basin, Brazil.

The use of improved cytogenetic techniques such as fluorescent in situ hybridization (FISH) has offered important methodologies for cytotaxonomic and evolutionary studies. In particular, the mapping of 5S rDNA sites has proved to be an excellent marker in the study of different organisms and, more recently, in fish. In the present work, the FISH technique was used to map the 5S rDNA sites in the chromosomes of eight neotropical fish species from the Paraíba do Sul river basin, four of these belonging to the order Characiformes, family Characidae, genus Astyanax (A. scabripinnis, A. parahybae, A. giton and A. intermedius) and four to the order Siluriformes, family Loricariidae (Neoplecostomus microps, Harttia loricariformis, Hypostomus affinis and Upsilodus sp.). Karyotype evolution aspects of the analyzed groups are discussed.