Overview: Medaka is Japanese rice fish and the scientific name is Oryzias latipes. Medaka, native to East Asia, is a denizen of rice paddies, ponds, a gently flowing stream. Excessive usage of fertilizer has reduced the number of medaka in Japan and now conservation status of medaka is “vulnerable”. Although the number of wild medaka is decreasing, the number of bred medaka is increasing. Now, there seems to be no concerns about them becoming endangered. The advancement of selective breeding has allowed us to admire their color. Some of them look like “Koi”, others look like popeyed goldfish. One of the most unique medaka is the so-called Hikari medaka. It emits light.