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Encyclopedia / Goldfish & Coldwater / Medaka
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Variations

9 kinds · tap one for a closer look

Medaka

Oryzias latipes · Ricefish, Japanese rice fish

Peaceful, hardy, unheated.

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4 cmBody length, without tail ✓
16–22 °CTemperature ✓
6.5–8pH ✓
40 LSmallest tank ✓
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Tank mates
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Not recommended
  • Medaka needs cool water and makes a lot of waste, while Cardinal tetra is tropical.
  • They need different temperatures (16–22 °C vs 23–29 °C). No setting suits both.
Not recommended
  • Medaka needs cool water and makes a lot of waste, while Serpae tetra is tropical.
  • Only a narrow temperature range suits both: exactly 22 °C.
Not recommended
  • Medaka needs cool water and makes a lot of waste, while X-ray tetra is tropical.
  • They need different temperatures (16–22 °C vs 24–28 °C). No setting suits both.
With conditions
  • Only a narrow temperature range suits both: 21–22 °C.
With conditions
  • Only a narrow temperature range suits both: 21–22 °C.
Compatible
Compatible
Compatible
Compatible
Compatible

138 species in our list are a good match.

Facts checked against sources on 16 Oct 2026. ✓ means a source backs it; ? means no reliable source yet. See sources

Care and water

Hardness ✓5–25 dGH
Group size ✓8 or more
Temperament ✓Peaceful
Swims at ?Top
Care level ✓Easy
Diet Omnivore
Lifespan ?Unknown
Size in shops 1.5–3 cm
Growth Fast

Behavior

Peaceful, hardy, unheated.

Food

Micro foods.

Tap a food to see what it is.

Male or female

Males have larger, convex dorsal and anal fins with long filament-like rays and a slightly slimmer body; females have smaller, non-convex fins and carry egg clusters from the vent after spawning.

Health

Common problems. Tap one to see the signs. This is a guide, not a diagnosis.

Breeding

Egg-depositor (plants) · Easy

Easy and prolific: eggs are fertilised as a single mass, hang from the female's vent for a while, then are brushed off singly or in small clumps onto plants or other media.

Pairing

Keep a group of 6+ adults.

Setup

A small tank or tub with plants or yarn.

What starts it

Warm water and long light hours.

Eggs

Females in good condition spawn a batch every few days or even daily; eggs hatch in about 1-3 weeks depending on temperature.

Raising the fry

Fry feed on infusoria then powdered foods.

Common mistakes
  • Not removing eggs
  • Cold water
  • Overcrowding
Full breeding guide, day-by-day plan and simulator →

Where it lives in the wild

RegionEast Asia – Japan, Korea & eastern China
Rivers and lakesRice-field waters of southern Japan
HabitatRice paddies, ponds and slow streams
Native rangeAbout 1,000 km across
See it on the world map

The story of the medaka

Medaka have long been kept in Japan and are a major lab model fish. In July 1994 four medaka flew on Space Shuttle mission STS-65 (IML-2); they mated and laid eggs that hatched normally, the first vertebrates to mate in space. Many colour strains exist.

Temminck and Schlegel described the medaka in 1846 in their 'Fauna Japonica'. Long kept in Japan as a pet, it later became an important model animal in biology. In 1994 medaka mated and laid eggs in space aboard the Space Shuttle Columbia.

First described by Coenraad J. Temminck & Hermann Schlegel in 1846.

  • Medaka were the first vertebrates to mate in space, in 1994.
  • It is a key model fish in genetics research.
  • Its common name 'ricefish' comes from its rice-paddy habitat.

Sources

17 facts checked with sources