Medaka, Oryzias latipes

Image Credit: NOZO/Wikipedia (CC 3.0)

The Medaka, also known as the Japanese killifish (Oryzias latipes) is part of the genus Oryzias (ricefish) – the only genus in the family Oryziinae. These natives of Southeast Asia are rather small measuring about 1-2 inches. The Medaka is also a native of rice paddies in coastal Asia. Because of the Medaka’s enjoyable coloration and hardiness it is a popular aquarium fish. Medaka’s coloration ranges from brown or yellow-gold in the wild, to white along with creamy yellow or orange. Since the 17th century in Japan the Medaka has been a popular pet. This fish moves between freshwater and salt water due to its amphidromous nature. This fish is also found in river and ocean habitats. The eggs are carried between the anal fins of the female.

Medakas are a model organism and are a substantial part in many areas of biological research. These fish are reproductively prolific and have short generation time. Medakas can be shipped easily and can resist cold. Researchers have analyzed nearly all aspects of the Medaka’s life cycle including their sexual behavior, spawning habits, pathology, feeding, genetic inheritance of coloration, ecology, embryological and much more.

The transgenic Medaka is relatively easy to produce. They have been genetically modified to secrete various human hormones and express promoter sequences from other fish. They make antimicrobial proteins and proteins that make the Medaka glow fluorescent green. Many mutations randomly appear in the Medaka such as a mutant strain that lacks scales and one strain with extra-long fins.

The Medakas have gone aboard the space shuttle into space. It was the first vertebrate to mate in orbit. After mating, a brood of healthy fry hatched onboard the space shuttle in 1994 on the Columbia.

Image Credit: NOZO/Wikipedia (CC 3.0)