Classical and molecular cytogenetics of Atherinella brasiliensis (Teleostei, Atheriniformes) from South coast of Brazil

Abstract

Cytogenetic studies were performed on specimens of Atherinella brasiliensis from Laranjeiras Bay (Paraná State, Brazil). All specimens had a diploid number of 48 chromosomes, with a karyotype constituted by 4m+14sm+18st+12a and fundamental number of 84. The C‐positive heterochromatin was distributed over the nucleolar organizer regions (NORs) in the centromeric regions and on short arms of metacentric and submetacentric chromosomes. Most of this heterochromatin was AT‐rich, except in the NORs, which were rich in GC, as detected by double staining with chromomycin A3/4′‐6‐diamin‐2‐phenylindole. Single NORs were located at terminal positions of a submetacentric pair, as confirmed by fluorescent in situ hybridization with 18S rDNA probes. Both techniques showed a size heteromorphism between the homologous chromosomes. The 5S rDNA clusters were located in terminal positions on two chromosomal pairs and also displayed a size heteromorphism. Despite the conserved diploid number, the data on the karyotype microstructure help characterize the cytogenetic profile of this group.