Medaka

Oryzias latipes

Also known as Japanese rice fish, Japanese ricefish

FreshwaterFish

Medaka (Oryzias latipes) — Seotaro · CC BY-SA 3.0

Care at a glance

Temperature: 61–72°F (16–22°C)
pH: 6.5–7.5
Adult size: 1.4 in (3.5 cm)
Minimum tank: 9 gal (35 L)
Temperament: Peaceful
Social behavior: Schooling
Swim level: Middle
Difficulty: Beginner
Breeding: Medium
Rarity: Rare
Origin: Japan, Vietnam, China, Korea
Family: Adrianichthyidae

Overview

Medaka are hardy, peaceful schoolers that swim in the middle and upper water and do best in a group. Feed a varied diet of flakes, micro-pellets, and small live or frozen foods like daphnia and mosquito larvae. They tolerate a wide range of conditions, which makes them a forgiving beginner fish, and they breed readily in spring and summer. A 35 liter tank or a small outdoor tub suits a group.

In the wild

Medaka, also called Japanese rice fish, live in slow streams, ponds, and rice paddies across Japan and parts of East Asia. Those are shallow, sun-warmed waters with some plants, and they swing through a wide temperature range over the year. In a tank they actually prefer it cooler than tropical, 16 to 22 C, so they suit an unheated indoor tank or an outdoor tub. Neutral to slightly alkaline water, pH 6.5 to 7.5, works well.

Good to know

Oryzias latipes is in the family Adrianichthyidae and grows to about 3.5 cm. It is an egg layer with an unusual habit. The female carries a cluster of fertilized eggs hanging from her vent for a while before brushing them onto plants, where they hatch in roughly one to two weeks depending on temperature. The IUCN lists it as Least Concern. It is a major lab animal, studied heavily in genetics and development.

Did you know

Medaka have been raised aboard spacecraft and were among the first vertebrates to mate and produce healthy young in orbit. Their see-through eggs let researchers watch development happen, which is part of why they fly as a model for how bodies and bone respond to low gravity.