Japanese rice fish

Medaka live in small ponds, shallow rivers, and rice fields.{{Cite journal|last1=牧人|first1=小林|last2=知尚|first2=頼経|last3=翔平|first3=鈴木|last4=彩美|first4=清水|last5=美香|first5=小井土|last6=優太郎|first6=川口|last7=洋一|first7=早川|last8=さやか|first8=江口|last9=弘文|first9=横田|last10=義和|first10=山本|date=2012|title=屋外池における野生メダカ Oryzias latipes の繁殖行動|journal=日本水産学会誌|volume=78|issue=5|pages=922–933|doi=10.2331/suisan.78.922|doi-access=free}} They can survive in a wide range of water temperatures ({{convert|0|-|42|C|F|disp=or}}), but they prefer a water temperature of {{convert|15|-|28|C|F}}.{{Cite journal|last1=Shima|first1=Akihiro|last2=Mitani|first2=Hiroshi|date=2004-07-01|title=Medaka as a research organism: past, present and future|journal=Mechanisms of Development|volume=121|issue=7|pages=599–604|doi=10.1016/j.mod.2004.03.011|pmid=15210169|s2cid=397672|issn=0925-4773}} Since they eat juvenile mosquitoes and small plankton, they are known as a beneficial organism for humans. They produce 10–20 eggs per birth, and they can produce eggs every day in laboratory conditions. They are seasonal breeding animals and usually lay eggs between spring and summer.{{Cite journal|last=Hirshfield|first=Michael F.|date=1980|title=An Experimental Analysis of Reproductive Effort and Cost in the Japanese Medaka, Oryzias Latipes|journal=Ecology|language=en|volume=61|issue=2|pages=282–292|doi=10.2307/1935187|issn=1939-9170|jstor=1935187|bibcode=1980Ecol...61..282H }} They prefer to lay eggs around water grass and often prefer living in rice fields. The egg usually requires 4–10 days to hatch.{{Cite journal|last=Iwamatsu|first=Takashi|date=2004-07-01|title=Stages of normal development in the medaka Oryzias latipes|journal=Mechanisms of Development|volume=121|issue=7|pages=605–618|doi=10.1016/j.mod.2004.03.012|pmid=15210170|s2cid=16570978|issn=0925-4773|doi-access=free}} They have an advanced renal function, which enables them to live in saltwater and brackish water.{{Cite journal|last1=Sakamoto|first1=Tatsuya|last2=Kozaka|first2=Tomohiro|last3=Takahashi|first3=Akiyoshi|last4=Kawauchi|first4=Hiroshi|last5=Ando|first5=Masaaki|date=2001-02-15|title=Medaka (Oryzias latipes) as a model for hypoosmoregulation of euryhaline fishes|journal=Aquaculture|volume=193|issue=3|pages=347–354|doi=10.1016/S0044-8486(00)00471-3|bibcode=2001Aquac.193..347S |issn=0044-8486}} The average life span of this species in the wild is estimated to be 2 years, though in laboratory conditions they can survive 3–5 years. They live in schools, and they can recognize the faces of other individual medaka.{{Cite journal|last1=Wang|first1=Mu-Yun|last2=Takeuchi|first2=Hideaki|date=2017-07-11|editor-last=Tsao|editor-first=Doris Y|title=Individual recognition and the 'face inversion effect' in medaka fish (Oryzias latipes)|journal=eLife|volume=6|pages=e24728|doi=10.7554/eLife.24728|pmid=28693720|pmc=5505697|issn=2050-084X|doi-access=free}}

File:School of Japanese killifish,Katori-city,Japan.JPG, Japan)]]

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.{{cite journal | author1 = Asai, T. | author2 = Senou, H. | author3 = Hosoya, K. | year = 2011 | title = Oryzias sakaizumii, a new ricefish from northern Japan (Teleostei: Adrianichthyidae) | journal = Ichthyol. Explor. Freshwaters | volume =22 | issue=4 | pages = 289–299| issn =0936-9902 }} This limits the native range of definite O. latipes to Japan: eastern and southern Honshu, Shikoku, Kyushu, and smaller southern islands in the country. 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.{{Cite iucn | author = Parenti, L. | title = Oryzias sinensis | volume = 2012 | page = e.T181312A1720540 | date = 2012 | doi = 10.2305/IUCN.UK.2012-1.RLTS.T181312A1720540.en }} The taxonomic position of certain populations, including some in China, Laos and east Korea, is unclear and require further study. 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. sinensis. The east Korean population is part of a clade with O. sakaizumii and O. latipes. Based on morphology it is closer to O. sakaizumii than O. latipes, but it may be an undescribed species.

O. latipes has been introduced to Hokkaido in northern Japan (where ricefish are not native).{{cite web | title = Oryzias latipes | url = https://www.nies.go.jp/biodiversity/invasive/DB/detail/50910e.html | website = Invasive species of Japan | publisher = National Institute for Environmental Studies (Japan) | access-date = 20 February 2017 }} 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).{{cite book | author1 = Kottelat, M. | author2 = Freyhof, J. | year = 2007 | title = Handbook of European freshwater fishes | publisher = Publications Kottelat, Cornol, Switzerland | isbn =978-2-8399-0298-4 }}

Phylogenetic analysis shows that the southern Japanese population was derived from that of the northern Kyushu area and spread into Honshu. On the other hand, the northern population was derived from a population from the Tajima-Tango region and spread alongside the Sea of Japan coast.{{Cite journal|last1=Katsumura|first1=Takafumi|last2=Oda|first2=Shoji|last3=Mitani|first3=Hiroshi|last4=Oota|first4=Hiroki|date=2019-01-01|title=Medaka Population Genome Structure and Demographic History Described via Genotyping-by-Sequencing|journal=G3: Genes, Genomes, Genetics|language=en|volume=9|issue=1|pages=217–228|doi=10.1534/g3.118.200779|issn=2160-1836|pmid=30482798|pmc=6325896}} O. latipes is known to have nine sub-populations: East Japanese type, East Setouchi type, West Setouchi type, San'in type, Northern Kyushu type, Osumi Type, Ariake type, Satsuma type and Ryukyu type. These sub-populations have been mixed with each other due to artificial releasing and decreasing local genetic diversity.{{Citation needed|date=April 2021}}

File:Killifish 1.jpg, photographed from above. Not to be confused with the brightly colored transgenic aquarium variants.]]

Oryzias latipes is a model organism and is extensively used in many areas of biological research, most notably in toxicology. Medaka have a short gestation period, and are reproductively prolific—characteristics that make them easy to rear in the laboratory. They can withstand cold and can be shipped easily. 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.{{cite book | author=Leroi, Armand Marie. | year=2003 | title=Mutants: On Genetic Variety and the Human Body. New York: Viking. | publisher=Penguin Publishing | isbn=0-670-03110-0 | url-access=registration | url=https://archive.org/details/mutantsongenetic00lero_0 }}{{cite web| url=https://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=DetailsSearch&Term=%22Oryzias%22%5BMajr%5D+AND+%22loattrfree+full+text%22%5Bsb%5D | title=Major topic "Oryzias": free full-text articles in National Library of Medicine}} It has a relatively small genome (~800 mega base pairs, half the size of the genome of another popular model fish, the zebrafish) as well as a generation time of 7 weeks (rather than 9 weeks for zebrafish) and hardier growth in a broad temperature range ({{convert|6|-|40|C|F|abbr=on|disp=or}}).{{cite web | url= http://www.geochembio.com/biology/organisms/medaka/ |title=Oryzias latipes, medaka as a model organism: taxonomy, facts, development stages, bibliography at GeoChemBio}}{{cite web | url= http://genome.ucsc.edu/cgi-bin/hgGateway?db=oryLat2 |title=Medaka (Oryzias latipes) Genome Browser Gateway}}

Transgenic medaka are relatively easy to produce. They have been genetically modified to secrete various human hormones, express promoter sequences from other fish, and to make antimicrobial proteins and a protein that makes the medaka glow fluorescent green, yellow or red.{{cite journal |vauthors=Tanaka M, Kinoshita M, Kobayashi D, Nagahama Y | year = 2001 | title = Establishment of medaka (Oryzias latipes) transgenic lines with the expression of green fluorescent protein fluorescence exclusively in germ cells: a useful model to monitor germ cells in a live vertebrate | journal = Proc Natl Acad Sci USA | volume = 98 | issue = 5 | pages = 2544–9 | pmid = 11226275 | pmc = 30174 | doi = 10.1073/pnas.041315498| bibcode = 2001PNAS...98.2544T | doi-access = free }} 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.{{cite journal | url=https://www.science.org/doi/abs/10.1126/science.1175151 | doi=10.1126/science.1175151 | title=Generation of Medaka Fish Haploid Embryonic Stem Cells | year=2009 | last1=Yi | first1=Meisheng | last2=Hong | first2=Ni | last3=Hong | first3=Yunhan | journal=Science | volume=326 | issue=5951 | pages=430–433 | pmid=19833967 | bibcode=2009Sci...326..430Y | s2cid=7505131 | url-access=subscription }}

File:Microgravity-promotes-osteoclast-activity-in-medaka-fish-reared-at-the-international-space-station-srep14172-s4.ogv

O. latipes carries the distinction of having been the first vertebrate to mate in orbit.{{cite web | url=http://cosmo.ric.u-tokyo.ac.jp/SPACEMEDAKA/IML2/e/text/textcontents_E.html | title=Medaka aboard Columbia | access-date=2006-07-16 | archive-date=2009-03-26 | archive-url=https://web.archive.org/web/20090326051644/http://cosmo.ric.u-tokyo.ac.jp/SPACEMEDAKA/IML2/e/text/textcontents_E.html | url-status=dead }} 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.{{Citation needed|date=April 2021}}

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.{{Cite journal|last1=Hilgers|first1=Leon|last2=Schwarzer|first2=Julia|title=The untapped potential of medaka and its wild relatives|journal=eLife|volume=8|doi=10.7554/eLife.46994|issn=2050-084X|pmc=6615862|pmid=31287418|year=2019 |doi-access=free }} By 1979, researchers had generated 10 inbred strains.{{Cite web|url=https://shigen.nig.ac.jp/medaka/strain/strain_definition.jsp|title=NBRP Medaka|website=shigen.nig.ac.jp|access-date=2019-10-07}} These inbred lines made medaka a model species for scientific research in genetics.{{Cite journal|last1=Kasahara|first1=Masahiro|last2=Naruse|first2=Kiyoshi|last3=Sasaki|first3=Shin|last4=Nakatani|first4=Yoichiro|last5=Qu|first5=Wei|last6=Ahsan|first6=Budrul|last7=Yamada|first7=Tomoyuki|last8=Nagayasu|first8=Yukinobu|last9=Doi|first9=Koichiro|last10=Kasai|first10=Yasuhiro|last11=Jindo|first11=Tomoko|date=June 2007|title=The medaka draft genome and insights into vertebrate genome evolution|journal=Nature|language=en|volume=447|issue=7145|pages=714–719|doi=10.1038/nature05846|pmid=17554307|issn=1476-4687|bibcode=2007Natur.447..714K|doi-access=free}}{{Cite journal|last1=Kimura|first1=Tetsuaki|last2=Shimada|first2=Atsuko|last3=Sakai|first3=Noriyoshi|last4=Mitani|first4=Hiroshi|last5=Naruse|first5=Kiyoshi|last6=Takeda|first6=Hiroyuki|last7=Inoko|first7=Hidetoshi|last8=Tamiya|first8=Gen|last9=Shinya|first9=Minori|date=2007-12-01|title=Genetic Analysis of Craniofacial Traits in the Medaka|url=https://www.genetics.org/content/177/4/2379|journal=Genetics|language=en|volume=177|issue=4|pages=2379–2388|doi=10.1534/genetics.106.068460|issn=0016-6731|pmid=18073435|pmc=2219511}} In 2014, work began on generating 111 different inbred lines derived from a single population collected in the wild.{{Cite journal|last1=Kirchmaier|first1=Stephan|last2=Naruse|first2=Kiyoshi|last3=Wittbrodt|first3=Joachim|last4=Loosli|first4=Felix|date=2015-04-01|title=The Genomic and Genetic Toolbox of the Teleost Medaka (Oryzias latipes)|url=https://www.genetics.org/content/199/4/905|journal=Genetics|language=en|volume=199|issue=4|pages=905–918|doi=10.1534/genetics.114.173849|issn=0016-6731|pmid=25855651|pmc=4391551}}

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.{{Cite journal|last1=Karigo|first1=Tomomi|last2=Kanda|first2=Shinji|last3=Takahashi|first3=Akiko|last4=Abe|first4=Hideki|last5=Okubo|first5=Kataaki|last6=Oka|first6=Yoshitaka|date=2012-07-01|title=Time-of-Day-Dependent Changes in GnRH1 Neuronal Activities and Gonadotropin mRNA Expression in a Daily Spawning Fish, Medaka|journal=Endocrinology|language=en|volume=153|issue=7|pages=3394–3404|doi=10.1210/en.2011-2022|pmid=22544888|issn=0013-7227|doi-access=free}}{{Cite journal|last=Kanda|first=Shinji|date=2018-11-27|title=Evolution of the regulatory mechanisms for the hypothalamic-pituitary-gonadal axis in vertebrates–hypothesis from a comparative view|journal=General and Comparative Endocrinology|volume=284|page=113075|doi=10.1016/j.ygcen.2018.11.014|pmid=30500374|s2cid=54468539 |issn=0016-6480}} Moreover, the medaka is the first non-mammalian vertebrate species for which a sex-determination gene (DMY) has been identified,{{Cite journal|last1=Matsuda|first1=Masaru|last2=Nagahama|first2=Yoshitaka|last3=Shinomiya|first3=Ai|last4=Sato|first4=Tadashi|last5=Matsuda|first5=Chika|last6=Kobayashi|first6=Tohru|last7=Morrey|first7=Craig E.|last8=Shibata|first8=Naoki|last9=Asakawa|first9=Shuichi|last10=Shimizu|first10=Nobuyoshi|last11=Hori|first11=Hiroshi|date=May 2002|title=DMY is a Y-specific DM-domain gene required for male development in the medaka fish|journal=Nature|language=en|volume=417|issue=6888|pages=559–563|doi=10.1038/nature751|pmid=12037570|issn=1476-4687|bibcode=2002Natur.417..559M|s2cid=4363239}} their sex is reversible by sex steroid manipulation,{{Cite journal|last1=Scholz|first1=S|last2=Gutzeit|first2=H. O|date=2000-10-01|title=17-α-ethinylestradiol affects reproduction, sexual differentiation and aromatase gene expression of the medaka (Oryzias latipes)|journal=Aquatic Toxicology|volume=50|issue=4|pages=363–373|doi=10.1016/S0166-445X(00)00090-4|pmid=10967398|bibcode=2000AqTox..50..363S|issn=0166-445X}} and they exhibit morphological sexual dimorphism between males and females. Furthermore, some methods such as ovariectomy{{Cite journal|last1=Kanda|first1=Shinji|last2=Akazome|first2=Yasuhisa|last3=Matsunaga|first3=Takuya|last4=Yamamoto|first4=Naoyuki|last5=Yamada|first5=Shunji|last6=Tsukamura|first6=Hiroko|last7=Maeda|first7=Kei-ichiro|last8=Oka|first8=Yoshitaka|date=2008-05-01|title=Identification of KiSS-1 Product Kisspeptin and Steroid-Sensitive Sexually Dimorphic Kisspeptin Neurons in Medaka (Oryzias latipes)|journal=Endocrinology|language=en|volume=149|issue=5|pages=2467–2476|doi=10.1210/en.2007-1503|pmid=18202129|issn=0013-7227|doi-access=free}} and altered light-dark cycles{{Cite journal|last1=Weber|first1=D. N.|last2=Spieler|first2=R. E.|date=1987-06-01|title=Effects of the light-dark cycle and scheduled feeding on behavioral and reproductive rhythms of the cyprinodont fish, Medaka,Oryzias latipes|journal=Experientia|language=en|volume=43|issue=6|pages=621–624|doi=10.1007/BF02126355|pmid=3595795|s2cid=11727260|issn=1420-9071}} have been developed to study the mechanism of reproduction in medaka.{{Citation needed|date=April 2021}}

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.{{Citation needed|date=July 2020}}

This species is increasingly used as a model in research relating to skeletal diseases in humans,{{Cite journal |last1=Di Biagio |first1=Claudia |last2=Dellacqua |first2=Zachary |last3=Martini |first3=Arianna |last4=Huysseune |first4=Ann |last5=Scardi |first5=Michele |last6=Witten |first6=Paul Eckhard |last7=Boglione |first7=Clara |date=2022-06-30 |title=A Baseline for Skeletal Investigations in Medaka (Oryzias latipes): The Effects of Rearing Density on the Postcranial Phenotype |journal=Frontiers in Endocrinology |volume=13 |doi=10.3389/fendo.2022.893699 |issn=1664-2392 |pmc=9281570 |pmid=35846331 |doi-access=free}} such as osteoporosis.

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.{{Cite journal|last1=Takehana|first1=Yusuke|last2=Nagai|first2=Naoko|last3=Matsuda|first3=Masaru|last4=Tsuchiya|first4=Kimiyuki|last5=Sakaizumi|first5=Mitsuru|date=October 2003|title=Geographic Variation and Diversity of the Cytochrome b Gene in Japanese Wild Populations of Medaka, Oryzias latipes|journal=Zoological Science|volume=20|issue=10|pages=1279–1291|doi=10.2108/zsj.20.1279|pmid=14569151|s2cid=22958328|issn=0289-0003|doi-access=free}} Many local communities try to preserve wild medaka in Japan.{{Cite web|url=https://www.tokyo-zoo.net/medaka/03.html|title=「東京めだか」を守っています ｜ 東京ズーネット|website=www.tokyo-zoo.net|access-date=2019-11-29}}{{Cite web|url=http://hamarepo.com/story.php?story_id=6808|title=追跡取材！ 進行中の「三浦メダカ」保全活動をレポート！ - はまれぽ.com 神奈川県の地域情報サイト|website=はまれぽ.com|access-date=2019-11-29}}{{Cite web|url=http://kodomo123.jp/1siryou/sizennsiryou/medakabunnpu.htm|title=和歌山市におけるのメダカの現在の生息状況|website=kodomo123.jp|access-date=2019-11-29}}

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 artificial release.{{Cite journal|last1=Nakao|first1=Ryohei|last2=Iguchi|first2=Yuka|last3=Koyama|first3=Naoto|last4=Nakai|first4=Koji|last5=Kitagawa|first5=Tadao|date=2017-01-01|title=Current status of genetic disturbances in wild medaka populations (Oryzias latipes species complex) in Japan|journal=Ichthyological Research|language=en|volume=64|issue=1|pages=116–119|doi=10.1007/s10228-016-0528-5|bibcode=2017IchtR..64..116N |s2cid=44688469|issn=1616-3915}} This will eliminate local genetic adaptations of each sub-population of medaka.{{Cite journal|last1=直人|first1=小山|last2=幹大|first2=森|last3=宏施|first3=中井|last4=忠生|first4=北川|date=2011|title=市販されているメダカのミトコンドリアdna 遺伝子構成|journal=魚類学雑誌|volume=58|issue=1|pages=81–86|doi=10.11369/jji.58.81}} Furthermore, since himedaka have vivid orange body color, the hybrids will attract more predators and thus decrease the total medaka population.{{Cite journal|last1=Nakao|first1=Ryohei|last2=Kitagawa|first2=Tadao|date=2015|title=Differences in the behavior and ecology of wild type medaka (Oryzias latipes complex) and an orange commercial variety (himedaka)|journal=Journal of Experimental Zoology Part A: Ecological Genetics and Physiology|language=en|volume=323|issue=6|pages=349–358|doi=10.1002/jez.1916|pmid=26054930|bibcode=2015JEZA..323..349N |issn=1932-5231}} In 2011, researchers discovered that almost 15% of wild-caught medaka in Nara had a himedaka-specific gene marker.{{Cite journal|last1=宏施|first1=中井|last2=遼平|first2=中尾|last3=昌司|first3=深町|last4=直人|first4=小山|last5=忠生|first5=北川|date=2011|title=ヒメダカ体色原因遺伝子マーカーによる奈良県大和川水系のメダカ集団の解析|journal=魚類学雑誌|volume=58|issue=2|pages=189–193|doi=10.11369/jji.58.189}} 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.{{Cite journal|last1=優秋|first1=田代|last2=康則|first2=上月|last3=陽一|first3=佐藤|last4=仁士|first4=村上|date=2005|title=外来種カダヤシによるメダカへの影響と保全策に関する一考察|journal=日本生態学会大会講演要旨集|volume=ESJ52|pages=814|doi=10.14848/esj.ESJ52.0.814.0}} The damage at the anal fin will decrease medaka offspring by preventing courtship behavior.{{Cite journal|last1=珠央|first1=伊藤|last2=右介|first2=小関|last3=靖章|first3=新妻|date=2006|title=メダカOryzias latipesにおける雄の鰭の損傷による産卵数および受精率の低下|journal=野生生物保護|volume=10|issue=1–2|pages=1–7|doi=10.20798/wildlifeconsjp.10.1-2_1}} 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.{{Cite web|url=https://www.env.go.jp/press/6802.html|title=環境省_未承認の遺伝子組換えメダカの回収のお願いについて|website=www.env.go.jp|access-date=2019-11-29}} 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.{{Cite journal|last1=Spivakov|first1=Mikhail|last2=Auer|first2=Thomas O.|last3=Peravali|first3=Ravindra|last4=Dunham|first4=Ian|last5=Dolle|first5=Dirk|last6=Fujiyama|first6=Asao|last7=Toyoda|first7=Atsushi|last8=Aizu|first8=Tomoyuki|last9=Minakuchi|first9=Yohei|last10=Loosli|first10=Felix|last11=Naruse|first11=Kiyoshi|date=2014-03-01|title=Genomic and Phenotypic Characterization of a Wild Medaka Population: Towards the Establishment of an Isogenic Population Genetic Resource in Fish|journal=G3: Genes, Genomes, Genetics|language=en|volume=4|issue=3|pages=433–445|doi=10.1534/g3.113.008722|issn=2160-1836|pmid=24408034|pmc=3962483}}   

File:Medaka - on the street in tokyo japan - july31-2021.webm, 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.{{Cite web|url=https://precious.jp/articles/-/7099|title=100万円の値がついた「高級メダカ」とは！？人気急上昇中、希少なメダカを一挙公開|website=ラグジュアリー体験の入り口メディア|language=ja|access-date=2019-11-29}} Currently, 456 commercial strains are documented and available for fishkeeping.{{Cite web|url=https://www.medakanoyakata.jp/?mode=f37|title=改良メダカ年表 - めだかの館|website=改良メダカ年表 - めだかの館|language=ja|access-date=2019-11-29}} 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.{{Citation needed|date=April 2021}}

{{Portal|Japan|Fish}}

• Mummichog (Fundulus heteroclitus), first fish sent to space in 1973

{{Reflist}}

{{Wiktionary|Medaka}}

{{Commons and category|Oryzias latipes|Oryzias latipes}}

{{Wikispecies|Oryzias latipes}}

• {{UCSC genomes|oryLat2}}
• [http://useast.ensembl.org/Oryzias_latipes/Info/Index/ Medaka genome] in Ensembl.
• [https://medakas.eu/ Medaka Fish Farm]
• [https://www.medakas.es/variedades/ Medaka Varieties, Strains and Colors.]
• [https://www.medakas.es/cria/ Guide on Breeding and Care of Oryzias latipes]

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Japanese rice fish

Category:Freshwater fish of Japan

Category:Animal models

Category:Taxa named by Coenraad Jacob Temminck

Category:Taxa named by Hermann Schlegel

Japanese rice fish

Category:Pets in Japan

Category:Endemic fish of Japan