artificial release. This will eliminate local genetic adaptations of each sub-population of medaka. Furthermore, since himedaka have vivid orange body color, the hybrids will attract more predators and thus decrease the total medaka population. In 2011, researchers discovered that almost 15% of wild-caught medaka in Nara had a himedaka-specific gene marker. In addition to these concerns, invasive species like mosquitofish compete with medaka by sharing the same habitat. A study reported that over 70% of medaka had their tail fins injured by attacks from mosquitofish. The damage at the anal fin will decrease medaka offspring by preventing courtship behavior. In 2006, it was found that a transgenic line of medaka was brought to Japan from Taiwan for commercial purposes. This transgenic line had an introduced gene which expresses green fluorescence, making the body glow. Now, this transgenic line has been released into the wild and is causing genetic pollution. There is no comprehensive study of population size of medaka, but the genomic analysis of one medaka sub-population indicates that their effective population size is around 25000–70000. Social importance in Japan The medaka has been kept as a domesticated pet in Japan for centuries. In recent years the fish has gained further popularity, with some rarer breeds valued at over 1 million yen (approximately US$10,000)—though the most common varieties (like himedaka) can be purchased for around 50 yen per fish. Currently, 456 commercial strains are documented and available for fishkeeping. Medaka are not only kept as pets but also widely utilized in education; Japanese elementary school classes often raise medaka in order to give the students firsthand experience with caring for live organisms, as well as to foster more broad appreciation for animals' life cycles. See also Mummichog (Fundulus heteroclitus), first fish sent to space in 1973 References External links Medaka genome in Ensembl. Japanese rice fish Fish of Japan Fish of East Asia Animal models Taxa named by Coenraad Jacob Temminck Taxa named by Hermann Schlegel Japanese rice fish