Medaka

Oryzias latipes

Also known as Japanese rice fish, Japanese ricefish, Backlight Killi

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: Egg layer · Medium
Rarity: Rare
Family: Adrianichthyidae
Origin: Japan, Vietnam, China, Korea

Overview

Medaka are hardy, peaceful schoolers that tolerate a wide range of conditions, which makes them a forgiving beginner fish.

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. That is part of why they fly as a model for how bodies and bone respond to low gravity.

Caring for the medaka

Medaka do well in an unheated indoor tank of at least 9 gal (35 L), or in a small outdoor tub. They are peaceful and community safe, and they do best in a group. They swim in the middle and upper water.

They prefer it cooler than tropical, at 61 to 72°F (16 to 22°C), with a neutral to slightly alkaline pH of 6.5 to 7.5. Feed a varied diet of flakes, micro pellets and small live or frozen foods like daphnia and mosquito larvae.

Medaka are egg layers with an unusual habit, and they breed readily in spring and summer. The female carries a cluster of fertilized eggs hanging from her vent for a while, then brushes them onto plants. The eggs hatch in roughly one to two weeks, depending on temperature.

Good to know

Oryzias latipes is in the family Adrianichthyidae, and it is also called the Japanese rice fish. It is a major lab animal, studied heavily in genetics and development. The IUCN lists it as Least Concern.

In the wild

Medaka live in slow streams, ponds and rice paddies across Japan and parts of East Asia. Those are shallow, sun-warmed waters with some plants. They swing through a wide temperature range over the year.

Weekly picks

Tank mates

The medaka is a peaceful, schooling species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.

Check the full mix in the stocking calculator

Common questions

What size tank does a medaka need?

A medaka needs at least 9 gal (35 L). It spends most of its time in the middle.

What temperature and pH does a medaka need?

A medaka is comfortable at 61–72°F (16–22°C) with a pH of 6.5–7.5.

What does a medaka eat?

A medaka eats a varied diet of flakes and micro pellets. Small live or frozen foods like daphnia and mosquito larvae round it out.

How big does a medaka get?

An adult medaka reaches about 1.4 in (3.5 cm).

Does a medaka need a group?

Yes. A medaka is a schooling species and should be kept in a group, not singly.

How does a medaka breed?

A medaka female carries a cluster of fertilized eggs hanging from her vent, then brushes them onto plants. The eggs hatch in roughly one to two weeks, and medaka breed readily in spring and summer.