Cytogenetic Studies in Some Apareiodon Species (Pisces, Parodontidae)

Abstract

Cytogenetic studies in 6 species of Apareiodon (Pisces, Parodontidae) from different Brazilian hydrographic basins showed a diploid number equal to 2n=54 chromosomes and the absence of morphologically differentiated sex chromosomes. Although the diploid and the fundamental numbers had been constant, some differences were observed concerning the karyotypic structure of the species. A. ibitiensis, Apareiodon sp. A and Apareiodon sp. B presented 50M/SM+4ST chromosomes, while A. piracicabae, A. vittatus and Apareiodon sp. C presented 52M/SM+2ST ones. Apareiodon piracicabae showed a polymorphism in relation to the number and position of the nucleolar organizer regions (NORs), while A. vittatus showed a variation in the NORs size. The available data indicate that the Parodontidae family have been submitted to a chromosomal diversification during their species differentiation process, despite the maintenance of the same diploid number.