Japanese ricefish
A hardy temperate surface fish kept in Japan for centuries and used worldwide as a laboratory model. Suits unheated tanks and outdoor containers, and breeds without any encouragement.
Quick profile
- Scientific name
- Oryzias latipes
- Adult size
- 3–4 cm (1.2–1.6 in)
- Lifespan
- 2–5 years
- Temperature
- 10–26 °C (50–79 °F)
- pH
- 7–8.5
- Hardness
- 6–25 °dGH
- Minimum tank
- 40 L (11 US gal)
- Minimum length
- 45 cm
- Swimming zone
- Upper level
- Social
- Shoaling — at least 6
- Diet
- Omnivore
- Overall confidence
- moderate confidence
What keeping this species involves
Exceptionally hardy across a wide temperature range, including unheated tanks.
Rice paddies, ditches and still shallow water; tolerates wide temperature swings.
Identity and names
- Common name
- Japanese ricefish
- Scientific name
- Oryzias latipes
- Family
- Adrianichthyidae
- Order
- Beloniformes
- Class
- Actinopterygii
- Also sold as
- medaka, Japanese killifish
Adult size and growth
3–4 cm (1.2–1.6 in)
Typical lifespan in an aquarium: 2–5 years. Almost every animal sold in a shop is a juvenile, so the tank has to suit the size in the first line rather than the size in the bag.
Shape, which is what the compatibility engine reads instead of length alone: fusiform — the ordinary torpedo with a small terminal mouth. Assigned from what is typical of Adrianichthyidae, not examined for this species.
Water and tank requirements
Small surface fish; surface area matters more than depth.
Temperature (°C)
Scale: 0 to 36 °C.
pH (pH)
Scale: 4 to 9.5 pH.
Hardness (°dGH)
Scale: 0 to 30 °dGH.
Where these figures come from
Habitat class
Rice paddy, ditch and drain — East Asian rice paddies and ditches
Shallow, still, sun-warmed managed water — agricultural rather than natural, and now the primary habitat of a number of aquarium species.
Enormous daily and annual temperature swing, low oxygen and shallow water. Species from here tolerate far more than a tropical community setting suggests, and several of them do not want to be kept at 26 °C all year.
- Conductivity
- 80–500 µS/cm
- Flow
- still
- Dissolved oxygen
- low
- Seasonality
- strong
These are figures for the KIND of water body, not measurements of this species. They are AquariumHQ’s summary of the general limnology and are given wide because the water is.
- TemperatureFollows the habitat this animal comes from
- Follows the water this animal is recorded from — East Asian rice paddies and ditches. Rice paddy, ditch and drain generally runs 15–34°C, and the advised band of 10–26°C is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
- pHFollows the habitat this animal comes from
- Follows the water this animal is recorded from — East Asian rice paddies and ditches. Rice paddy, ditch and drain generally runs 6–7.8, and the advised band of 7–8.5 is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
- General hardnessFollows the habitat this animal comes from
- Follows the water this animal is recorded from — East Asian rice paddies and ditches. Rice paddy, ditch and drain generally runs 2–15 dGH, and the advised band of 6–25 dGH is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
Scale: 6.4 to 37.6 °C.
Scale: 5.6 to 8.9 pH.
Scale: -1.4 to 28.5 dGH.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 10–26 °C (50–79 °F) | Stability matters more than hitting an exact figure. |
| pH | 7–8.5 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 6–25 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 40 L (11 US gal) | A floor, not a recommendation. |
| Minimum footprint | 45 cm long | Small surface fish; surface area matters more than depth. |
| Water flow | still | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
Behaviour
- Females carry eggs visibly attached below the vent for hours before depositing them.
Telling males from females
Males have a larger, notched dorsal fin and a longer anal fin.
Feeding
- Diet type
- Omnivore
- Staples
- Small dry foods, Frozen daphnia, Baby brine shrimp, Mosquito larvae
Breeding
- Strategy
- Females carry a cluster of eggs attached below the body before depositing them on plants
- Difficulty
- incidental
- Parental care
- none
Tankmates and compatibility
Assessments are derived from stored traits by the compatibility engine, with the reasoning shown. A verdict is a statement about probability, not a guarantee — individual temperament can override it.
| Towards | Risk | What it means |
|---|---|---|
| Small fish | none | Anything that fits in the mouth is at risk once this species reaches adult size. |
| Adult dwarf shrimp | none | Cover reduces losses but rarely prevents them where the risk is high. |
| Shrimplets | moderate | Determines whether a shrimp colony can grow rather than merely persist. |
| Snails | none | Applies to snails you wanted as well as snails you did not. |
| Long or trailing fins | none | Fin damage is an entry point for secondary infection. |
| Plants | none | Tough species such as Anubias and Java fern survive most grazers. |
Any pair in the catalogue can be assessed with the compatibility checker.
Welfare considerations
Points where the way this species is commonly sold or kept differs from what it actually needs.
- Do not keep at tropical temperatures year-round; the species does better with a cool season.
Problems to watch for
Most problems in a tank containing this species are general rather than species-specific. Start with the troubleshooting index and work from the observation rather than from a guess at the cause.
What AquariumHQ does not yet hold
Species-level disease susceptibility is modelled in the graph and is not yet populated. Health pages will not be published until each condition has veterinary sourcing, because health content written without evidence is the most harmful thing this product could publish. The gap is recorded in the coverage report.
Where it comes from
- Native range
- Japan, Korea, eastern China
- Habitat
- Rice paddies, ditches and still shallow water; tolerates wide temperature swings.
What the checklists say
22 distribution statements retrieved from GBIF checklists. Establishment means is reproduced from the source where it states one, and left unstated where it does not — a record of presence is not a record of origin.
| Status | Places | What this means |
|---|---|---|
| Introduced | 17 | A checklist states the species arrived here with human help. That is not a statement that it is established, harmful or illegal. |
| Recorded as present, establishment means not stated | 5 | The source records the species as present and does not say whether it is native or introduced. AquariumHQ does not fill that in. |
No checklist AquariumHQ holds positively calls this species native anywhere, so the native range above rests on AquariumHQ’s own reading of the literature rather than on a cited checklist.
Legal status and responsible practice
Where this species has been introduced, and what followed
Europe — a single Russian record from 1974
Establishment unclearAquaculture escape, recorded from one Russian locality in 1974 and nowhere else in Europe since. The medaka is a laboratory model organism as well as an ornamental fish, and this is the pathway EASIN records rather than either of those.
- Escape from food or bait aquacultureFood and bait production, at a scale no private keeper approaches. The animals are held in numbers, in ponds, often on floodplains.
What has been established
Nothing. The species is present outside its native range and no study has measured what it does there. The absence of data is not the absence of effect — it means the question has not been asked, and this is the ordinary state of the evidence for most aquarium species that have established somewhere warm.
EASIN — European Alien Species Information Network · EASIN catalogue record R10539 (apixg/catxg) · read 2026-08-30. A European network: the routes and effects recorded here are the ones documented in Europe. EASIN compiles national inventories, DAISIE and CABI rather than measuring, and its pathway assignments carry its own uncertainty flags, which are reported above where it sets them.
Never release aquarium life into the wild
Aquarium animals, plants, and aquarium water must never be released into ponds, rivers, canals, drains or the sea — not even in a country where the species is sold freely. Released fish and invertebrates establish populations that displace native species, and released plants and water carry pathogens, parasites and fragments capable of spreading without any animal at all. If you can no longer keep an animal, rehome it through an aquarium society, a retailer that accepts returns, or another keeper.
- Rehome through a local aquarium society, a specialist retailer or another keeper.
- Unwanted plants go in household waste or a hot compost heap, never in a watercourse or a garden pond.
- Never empty a bucket of tank water into a drain that discharges to open water.
- If an animal is beyond rehoming, ask an aquatic veterinarian about humane euthanasia rather than releasing it.
Legal status is recorded from the sources named and was correct on the verification date shown. Rules change, and sub-national rules often differ from national ones. Check the current position with the relevant authority before acquiring, selling or moving any animal or plant.
Evidence
Every stored value with the kind of support behind it and where to check it. Evidence type and confidence are separate axes: an editorial position held confidently and a measurement held tentatively are different things.
| Claim | Value | Evidence type | Confidence | Source |
|---|---|---|---|---|
| scientific name | Oryzias latipes | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Japan, Korea, eastern China | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 3–4 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 2–5 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 10–26 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 7–8.5 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 6–25 °dGH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 40 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 45 cm | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum group size | ≥ 6 | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
Last reviewed 2026-08-10. Values labelled as an aquarium-literature consensus are AquariumHQ editorial positions rather than measurements — see how evidence is handled.
Why we say this
What each figure on this page rests on, and how far that is from being independently established.
Every figure on this page has a provenance. Open any claim to see what AquariumHQ holds for it, which sources say what, and what a claim of that kind actually needs. Different claims need different evidence: an accepted scientific name is settled by one authority, while a legal restriction needs a current primary instrument. A single source is often the right answer rather than a thin one.
scientific nameAquariumHQ's own position, externally checkableBased on a verified authoritative source.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: accepted scientific name and classification — 1 authoritative source in an appropriate context. Checked against gbif on 2026-08-12. One authoritative backbone is what this class requires.
What would improve this: Go and read a source. This is reachable and has not been reached.
native rangeAquariumHQ's own position, externally checkableBased on a verified authoritative source.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: where the species occurs — 1 authoritative source in an appropriate context. 22 distribution statements held from GBIF checklists — introduced in 17 country. Establishment means is reproduced from the source, never inferred from occurrence.
What would improve this: Go and read a source. This is reachable and has not been reached.
adult sizeOne sourceAquariumHQ's own position, derived from evidenced inputs.1 citation, 1 independent origin
A single source: usgs-nas.
- 4 cm — USGS Nonindigenous Aquatic Species database · Maximum recorded · Observed in the wild · checked 2026-08-29
What this kind of claim needs: size a well-kept specimen reaches — no external source is required, provided AquariumHQ shows its reasoning. A documented maximum is held and the catalogue's typical adult range is stated separately, with the relationship between them recorded rather than collapsed. The catalogue's typical adult range already reaches the largest recorded specimen.
What would improve this: Corroborate against a second, independent source.
lifespanAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
temperatureAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
phAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
general hardnessAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
minimum tank volumeAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: minimum tank size — no external source is required, provided AquariumHQ shows its reasoning. No authority publishes this. AquariumHQ derives it, and the derivation is recorded with its inputs and assumptions.
What would improve this: Keep the rationale current. There is no source to find.
minimum tank lengthAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: minimum tank size — no external source is required, provided AquariumHQ shows its reasoning. No authority publishes this. AquariumHQ derives it, and the derivation is recorded with its inputs and assumptions.
What would improve this: Keep the rationale current. There is no source to find.
minimum group sizeAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: group size — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Keep the rationale current. There is no source to find.
Guides relevant to this species
Chosen from this record's own traits rather than listed on every page.
- Schooling and shoalingThis species is recorded as shoal, and the number it is kept in decides how it behaves.
- The kinds of water aquarium fish come fromThis record's water bands follow rice paddy, ditch and drain, which is the kind of water this animal is recorded from.
- How aquarium species get into the wildThis species has a documented introduction outside its native range, with the route recorded.
Group size and social behaviour
Loose shoaler; males display and spar mildly.