Chromosomal diversification of reef fishes from genus Centropyge (Perciformes, Pomacanthidae) Paulo Roberto Antunes de Mello Affonso & Pedro Manoel Galetti Jr.* Departamento de Gene´tica e Evoluc ¸a ˜o, Universidade Federal de Sa ˜o Carlos, Via Washington Luı´s, Km 235, Caixa Postal 676, 13565-905 Sa ˜o Carlos SP, Brazil; *Author for correspondence (Phone: +55-16-260-8309; Fax: +55-16-260-8306; E-mail: galettip@power.ufscar.br) Received 9 April 2004 Accepted 14 August 2004 Key words: biogeography, dispersal, FISH, heterochromatin, NOR, pericentric inversion, Pomacanthidae 5S, 18S Abstract The genus Centropyge is remarkable for species richness, composing a highly specialized fish group amongst members from family Pomacanthidae. However, cytogenetical reports are nearly absent in these animals. New data are provided from karyotypical studies carried out on Centropyge aurantonotus from the Brazilian coast of the Atlantic Ocean and C. ferrugatus from the Philippines Sea of the Indo-Pacific Ocean. Both species present 2n ¼ 48 but karyotypes are differentiated by fundamental number. C. aurantonotus has a great number of biarmed chromosomes (4 m + 14 sm+16 st+4 a), while C. ferrugatus presents only acrocentric chromosomes. Single nucleolar organizer regions (NORs) are located at interstitial position of an acrocentric pair in C. ferrugatus and on short arms of a subtelocentric pair in C. aurantonotus, as confirmed by fluorescent in situ hybridization (FISH) with 18S rDNA probes. Heterochromatin is dis- tributed over NOR and centromeric regions in both species, but additional GC-rich heterochromatic blocks on short arms of up to eight chromosomal pairs can be detected in C. aurantonotus. 5S rDNA segments were located interstitially on two chromosomal pairs in C. ferrugatus and on nine pairs in C. aurantonotus, mostly equivalent to heterochromatic blocks on short arms of biarmed chromosomes. C. ferrugatus can be considered a species in which basal chromosomal features proposed for modern Teleosteans were con- served. The derived karyotype pattern of C. aurantonotus seems to be determined by pericentric inversions and heterochromatin addition which probably determined the notorious dispersion of 5S rRNA (pseu- do)genes. It is demonstrated that, even within a group generally characterized by cytogenetical homoge- neity as the family Pomacanthidae, diversified karyotypes can be found. Introduction Pomacanthidae is a specialized fish family, com- posed by about nine genera and more than 80 species, all associated with coral reefs and wide- spread throughout the Atlantic, Indian and Pacific Oceans (Johnson & Gill, 1995). The genus Centropyge is a very specious Pom- acanthidae group (nearly 40 species), with recent descriptions of new species (Pyle, 1990; Pyle & Randall, 1993). Representatives of this genus are popularly known as pigmy angelfishes, as a refer- ence to their small size when compared to the correlated species. This feature and their beautiful color patterns make these fishes popular for or- namental aquarium (Hunziker, 1992). Further- more, Centropyge species are some of most studied angelfishes under behavioral and reproductive fo- cus, mainly concerned to the presence of protog- ynous hermaphroditism (Bauer & Bauer, 1981). Genetica (2005) 123: 227–233 Ó Springer 2005