yellow or red. There are also many mutations that show up in medaka at random, for example, a mutant strain that lacks scales, and one with extra-long fins. Haploid embryonic stem cell lines have been established. In space O. latipes carries the distinction of having been the first vertebrate to mate in orbit. The result of the mating was a brood of healthy fry, hatched on the Space Shuttle Columbia in 1994. O. latipes returned to space in 2012, launched aboard a Soyuz spacecraft Soyuz TMA-06M and housed in an aquarium aboard the International Space Station. Inbreeding lines The possibility of serial inbreeding facilitates genetic research due to reduction of heterozygous sites in the genome. In medaka it is relatively easy to establish inbred lines, unlike other model species like zebrafish and mice. By 1979, researchers had generated 10 inbred strains. These inbred lines made medaka a model species for scientific research in genetics. In 2014, work began on generating 111 different inbred lines derived from a single population collected in the wild. Sex and reproduction Medaka reproduce on a daily basis, which is an optimal trait for studying their reproductive biology. Researchers have studied HPG axis activities intensively in this species. Moreover, the medaka is the first non-mammalian vertebrate species for which a sex-determination gene (DMY) has been identified, their sex is reversible by sex steroid manipulation, and they exhibit morphological sexual dimorphism between males and females. Furthermore, some methods such as ovariectomy and altered light-dark cycles have been developed to study the mechanism of reproduction in medaka. Immunology 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. Conservation Status The medaka is listed as a least-concern species in the IUCN red list. The justification of this categorization is that this species is living in widespread habitat (755,000 km2) and is relatively abundant in its various habitats. However, it is considered an endangered species by Japan's Ministry of the Environment. Many local communities try to preserve wild medaka in Japan. Concerns There are two major concerns about medaka conservation: habitat degradation and hybridization with domesticated medaka (himedaka). Due to modernization of rice fields and irrigation canals, optimal places for medaka reproduction are massively decreasing. In addition, recent studies confirmed that himedaka have been introduced into many local regions by