PRIMARY RESEARCH PAPER Stable karyotypes: a general rule for the fish of the family Prochilodontidae? Maria Leandra Terencio • Carlos Henrique Schneider • Maria Claudia Gross • Marcelo Ricardo Vicari • Eliana Feldberg Received: 14 July 2011 / Revised: 9 January 2012 / Accepted: 15 January 2012 / Published online: 1 February 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Cytogenetic studies involving the family Prochilodontidae have shown that these fish can be characterized by a constant diploid number and a conserved karyotypic macrostructure. This study focused on comparative physical chromosomal map- ping using 18S and 5S rDNA to compare the species Semaprochilodus insignis and S. taeniurus. Our results indicated the conservation of large number of con- ventional chromosomal markers. The molecular cyto- genetic analyses of the location of the 18S rDNA indicated the maintenance of a chromosome pair bearing these sites in both species analyzed, and it appears to be a conserved character among the majority of the species of this family. The stability of the number of 5S ribosomal DNA sites and their chromosomal localization as has been reported for the Prochilodontidae was not, however, confirmed for S. insignis and S. taeniurus, as these species showed multiple specific rDNA 5S sites. As such, and in spite of the fact that a number of studies indicate that the family Prochilodontidae has a conserved karyotypic structure, the utilization of molecular tools that use chromosomal segments as markers revealed that this presumed stability cannot be extended to the genome level for the species S. insignis and S. taeniurus. Keywords FISH Á 18S rDNA Á 5S rDNA Á Comparative cytogenetics Á Semaprochilodus spp. Á Amazon River basin Introduction The family Prochilodontidae comprises 21 fish species distributed in three genera: Ichthyoelephas, Prochil- odus, and Semaprochilodus. The systematics of this family is somewhat complex due to the extraordinary stability of the morphological and meristic traits used to distinguish its species (Mago-Leccia, 1972). The genus Semaprochilodus is composed of six species popularly known as ‘‘jaraqui,’’ of which only Semaprochilodus insignis (Jardine & Schomburgk, Handling editor: Koen Martens M. L. Terencio (&) Á C. H. Schneider Á E. Feldberg Laborato ´rio de Gene ´tica Animal, Instituto Nacional de Pesquisas da Amazo ˆnia—INPA/CPBA, Coordenac ¸a ˜o de Pesquisas em Biologia Aqua ´tica, Av. Andre ´ Arau ´jo, 2936, Petro ´polis, Manaus, AM 69011-970, Brazil e-mail: leandra@inpa.gov.br M. C. Gross Departamento de Biologia, Laborato ´rio de Citogeno ˆmica Animal, Universidade Federal do Amazonas, Instituto de Cie ˆncias Biolo ´gicas, Manaus, AM, Brazil M. R. Vicari Departamento de Biologia Estrutural, Laborato ´rio de Citogene ´tica e Evoluc ¸a ˜o, Universidade Estadual de Ponta Grossa, Molecular e Gene ´tica, Ponta Grossa, PR, Brazil 123 Hydrobiologia (2012) 686:147–156 DOI 10.1007/s10750-012-1006-3