FISH-mapping of 18S ribosomal RNA genes and telomeric sequences in the Japanese bitterlings Rhodeus ocellatus kurumeus and Tanakia limbata (Pisces, Cyprinidae) reveals significant cytogenetic differences in morphologically similar karyotypes.

The Japanese rose bitterling, Rhodeus ocellatus kurumeus, and the oily bitterling, Tanakia limbata, were cytogenetically studied by silver (Ag)- and chromomycin A3 (CMA3)-staining, by C-banding and by mapping of the 18S ribosomal genes and of the (TTAGGG)n telomeric sequence. These two representative species of related genera of the subfamily Acheilognathinae show very similar chromosome complements. Nevertheless, significant differences in the chromosomal distribution of nucleolus organizer regions (NORs) and interstitial telomeric sequences were observed. Whereas R. ocellatus kurumeus shows a single NOR-bearing chromosome pair, T. limbata is characterized by a higher number of variable NORs. Multiple telomeric sequence sites were found at the pericentromeric regions of several chromosomes in the rose bitterling. No telomeric sequence sites were detected near centromeres, but they were found to be scattered along the NORs in the oily bitterling. Two karyoevolutive trends might have been identified in the subfamily.