Cytogenetical characterization of Odontesthes bonariensis (Pisces,Atherinidae), an Argentine species introduced in Italy

Giemsa and Ag-staining techniques and C-banding were performed on cytological preparations of 22 specimens of silversides (Odontesthes bonariensis) in order to extend the karyological knowledge on the family Atherinidae, to contribute cytotaxonomically to the systematics of the species and to identify possible cytogenetical markers of the introduced population.The karyotype is conservative, 2n being 48, and 44 chromosomes being uniarmed. The remaining four biarmed chromosomes show intraindividual morphological variability. This variability is sex-independent. Ag-stanining techniques reveal that NORs are located on the short arms of biarmed chromosomes and that the morphological variability is partially due to NOR activity. C-banding revealed the associations between NORs and constitutive heterochromatin which could be responsible for some apparent structural differences. The differences found could be cytogenetical markers of the introduced population.Research work supported by CNR, Italy. Special grant I.P.R.A. — Sub-project 1. Paper No. 1192.