Taxonomy & naming
Asai, Senou and Hosoya described the species in 2012 from an irrigation canal in the Nakaikemi wetland at Tsuruga, Fukui Prefecture. It was separated from Oryzias latipes after genetic work showed two deeply divergent groups of Japanese medaka. The name honours Sakaizumi, a Japanese geneticist who worked on medaka.
Morphology
Very close to O. latipes in appearance, and the two are best told apart by genetics and, to a degree, by differences in the body and dorsal fin. FishBase gives a maximum of 1.5 in SL.
Habitat
Rice paddies, ditches, ponds and marshes in northern and Sea of Japan-side Honshu. FishBase describes irrigation canals among paddy fields in flat alluvial lowlands, and says the species is well adapted to temporary floodplain wetlands. Its range runs along the Sea of Japan coast from Aomori to Hyogo Prefecture. The type locality is the Nakaikemi wetland, Fukui.
Feeding
A small invertebrate and algae feeder like other medaka.
Mating
Courtship follows the usual Oryzias pattern, with the male following the female and wrapping his fins around her.
Breeding
As with the Japanese medaka, females carry the egg cluster briefly and then deposit it on plants.
In the aquarium
Occasionally kept by medaka enthusiasts, and kept in the same way as O. latipes: unheated, planted, with small live and prepared foods. Local strains should not be mixed with other medaka stocks.
Conservation
The IUCN Red List assessed Oryzias sakaizumii as Least Concern in 2018. Medaka habitats across Japan have been reduced by changes to paddies and water channels.