Medaka Ricefish

Scientific name: Oryzias latipes

Adult size: about 3.5 cm

Origin: Japan, Korea, China, Taiwan and Vietnam

Water: 16–22 °C, pH 6.5–8.5, 5–25 dGH

Group: 8 or more

Diet: micropredator, small live, frozen and dried foods

Temperament: peaceful, surface-dwelling

The medaka, or Japanese ricefish, is a slender surface-dwelling fish of about 3.5 cm, kept in Japan for centuries and now bred in many colour forms including orange, white, blue and platinum. It ranges across Japan, Korea, eastern China, Taiwan and Vietnam, living in rice paddies, ditches and slow streams. Its real advantage is temperature: Seriously Fish gives 16–22 °C as the range, which makes it one of the few options for an unheated indoor tank, and it tolerates hard, alkaline water well. It is peaceful and does best in a group of eight or more, where it behaves confidently and spawns readily. Females carry a cluster of eggs at the vent for hours before brushing them onto plants or a spawning mop, and eggs hatch in one to three weeks depending on temperature. It is a micropredator, feeding on small crustaceans and insect larvae at the surface, and it will accept dried foods but does best with regular small live and frozen fare.

Water: 16–22 °C and pH 6.5–8.5, hardness 5–25 dGH. It is comfortable at room temperature in most Australian homes; avoid prolonged warm tropical temperatures. Keep water clean with regular partial water changes.

Tank and planting: a shallow, well-planted tank with floating plants or fine-leaved stems for spawning, gentle flow and a lid, since it lives at the surface and can jump.

Feeding: small floating or slow-sinking dried foods plus daily live or frozen daphnia, brine shrimp and chopped bloodworm. Feed small amounts, and remove anything uneaten.