Medaka, Oryzias latipes

Medaka (Oryzias latipes), also known as the Japanese killifish, is a species of ricefish and the only member of the Oryziinae subfamily. It is native to Southeast Asia and is a common occupant of rice paddies in coastal Asia. It is amphidromous, meaning it moves between salt and freshwater at some point during life, and for this reason, is found in both ocean and river habitats.

This is a small fish, reaching lengths of 0.75 to 1.55 inches. Due to its hardiness and pleasant coloration, this fish has become a popular aquarium species. It varies in color from brown to yellow-gold in the wild to white, creamy yellow, or orange in aquarium-bred individuals. It has been a popular aquarium pet since at least the 1600s in Japan.

This species is considered a model organism and has been extensively used in many areas of biological research. Its short gestation period high reproductive fertility makes them easy to rear in the laboratory. They can withstand cold temperatures and ship easily. The Medaka has been extensively analyzed and its genome has been fully sequenced.

Its sexual behavior, genetic inheritance to coloration, spawning habits, feeding, ecology, etc. have all been strongly studied.

Scientists have genetically modified Medaka 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.

The Medaka has long been used in space programs and has flown aboard the space shuttle on at least three different missions. It also carries the distinction of having been the first vertebrate to mate in orbit. The mated fish gave birth to a brood of healthy fry aboard the space shuttle Columbia in 1994.

The Medaka has also recently gained fame by being the first marine animal to live on the International Space Station. The Japanese Space Agency recently launched the Aquatic Habitat, which will study the effects space has on the fish as they live on the orbiting space lab for three months, from July 2012 to mid-October.

Image Caption: Japanese ricefish, Japanese killifish(Oryzias latipes). Credit: NOZO/Wikipedia  (CC BY 3.0)