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Oryzias latipes, also known as the medaka Japanese rice fish, and Japanese killifish, is a small (2-4 cm long) fish, one of the 27 species in the ricefish family Adrianichthyidae. Native to Southeast Asia, the medaka lives in slow-moving streams, coastal tide pools and rice paddies. A popular pet in Japan since the 17th century, it is now regularly found in the aquarium trade. Medaka are hardy fish that do well in a range of temperatures and water salinities; in the wild they migrate between fresh and salt water areas, and are thus common along coastal regions, in aquaria they prefer at least slightly brackish water. Genetically modified fish have been marketed that contain cells which express florescent jellyfish proteins, so that these fish glow red, green or yellow. Unlike most of the other fish in the genus Oryzias which spawn their eggs, female O. latipes carry their eggs, about 20 at a time, in a cluster that resembles a bunch of grapes between her anal fins, where they are they externally fertilized by the males. The female then carries them for a day or more before depositing the eggs individually on aquatic plants. In addition to being popular pets, starting in the late 1800s medaka were developed as a research animal for studying vertebrate development. Their genome (which is quite small) has been entirely sequenced, and they joined the crew of the Space shuttle Columbia in 1994, where they became the first vertebrate to mate and produce normal young under conditions of weightlessness.

(Burgess 2005”; Ijiri 1995; The aquarium wiki 2011; Wikipedia 2011)


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