This small (up to about 3.6 cm or 1.4 in) native of Japan is a denizen of rice paddies, marshes, ponds, slow-moving streams and tide pools.

Bright yellow, red or green transgenic populations, similar to GloFish, have also been developed, but are banned from sale in the EU.

[6] After fertilization, the female carries her eggs attached anterior to the anal fin for a period before depositing them on plants or similar things.

[12] As originally defined, O. latipes was native to much of east and mainland southeast Asia, but in recent decades most of these populations have been split off as separate species based on morphological (morphometrics and meristics) and genetic evidence.

[13] Formerly included in this species but now regarded as separate are O. sakaizumii in northwestern Honshu in Japan (locally, it hybridizes with O. latipes), and O. sinensis (Chinese rice fish) in much of China, west Korea and parts of mainland southeast Asia.

[4][13][14] The taxonomic position of certain populations, including some in China, Laos and east Korea, is unclear and require further study.

[4][13] It is possible that all these Chinese populations are part of O. sinensis, but the Laos specimens are relatively large, similar to O. latipes rather than the tiny O.

[15] There are other reports of introductions around the world, but at least most of those in mainland Asia and Europe involve O. sinensis (Chinese rice fish).

[15][16] Phylogenetic analysis shows that the southern Japanese population was derived from that of the northern Kyushu area and spread into Honshu.

[citation needed] Oryzias latipes is a model organism and is extensively used in many areas of biological research, most notably in toxicology.

Nearly all aspects of the life cycle of medaka have been analyzed by researchers including sexual behavior, genetic inheritance of coloration, spawning habits, feeding, pathology, embryological development, ecology, etc.

[citation needed] The possibility of serial inbreeding facilitates genetic research due to reduction of heterozygous sites in the genome.

[citation needed] The discovery that T-lymphocytes home to the thymus in medaka has led to an understanding that this is not specific to mammalians but can be found in other vertebrates.

Due to modernization of rice fields and irrigation canals, optimal places for medaka reproduction are massively decreasing.

[41][42] Furthermore, since himedaka have vivid orange body color, the hybrids will attract more predators and thus decrease the total medaka population.