Rediscovery of Oryzias hubbsi with notes on its reproductive isolation with O. javanicus

Oryzias hubbsi Roberts 1998 is a miniature species of adrianichthyid (medaka). It was described based on a laboratory stock bred from individuals collected in the field in 1983. No individuals of this species have been collected in the field since then. Mitochondrial haplotyping revealed that individuals collected from a fishing pond at Tangerang, west of Jakarta, were Oryzias javanicus (Bleeker 1854), a closely related common species widely distributed throughout the Sunda Islands, as well as O. hubbsi. Phylogenetic network and population genetic structure analyses on the basis of genome-wide single-nucleotide polymorphisms revealed that O. hubbsi and O. javanicus individuals are clearly separated from each other, indicating that they do not hybridize. Morphometric and meristic characters of the newly discovered O. hubbsi individuals were consistent with those of previous studies. We discussed the reasons for the lack of reports of O. hubbsi since the 1980s and the mechanisms of reproductive isolation between O. hubbsi and O. javanicus.