Home / Fishes / Ricefish, halfbeaks, needlefish / Japanese rice fish
No federal permit to keepJapanese rice fish
Oryzias latipes
Fishes › Ricefish, halfbeaks, needlefish (Beloniformes) › Adrianichthyidae (Ricefish and medaka)
The Japanese rice fish (Oryzias latipes), also known as the medaka, is a member of genus Oryzias (ricefish), the only genus in the subfamily Oryziinae.
Care at a glance
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 1.6 in / 4 cm).
- Water: Freshwater (tolerates brackish).
- Temperature: 64–75°F (range recorded for this species).
- pH: 7–8.
- Hardness: 9–19 dGH.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: Eats a varied diet: mix quality prepared foods with frozen and live foods. FishBase classes it as a omnivore.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 18 × 12 in (roughly 11 US gallons); space needed is rated “modest tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 61–72 °F, pH 6.5–8.5, 5–25 dGH.
- Behaviour: temperament peaceful; a shoaling fish best kept in a group of six or more; suited to a community tank.
- Difficulty: Easy (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Best maintained in a heavily planted set-up, ideally with a dark substrate, patches of dense vegetation, and some open areas.”
- Diet: “A micropredator feeding on small insects, worms, crustaceans and other zooplankton in nature.”
- Tankmates: “Generally peaceful but doesn't make an ideal addition to many communities due to its environmental requirements.”
- Breeding: “Quite easy to breed and fairly prolific, with females capable of producing batches of eggs every few days or even on a daily basis when in good condition.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Ricefish and medaka
Applies to most species in this group. Habitat: Ricefish occupy Asian rice paddies and other shallow fresh/brackish habitats, while several listed Sulawesi species inhabit ancient freshwater lakes (medaka, sulawesi). Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- O. latipes: at least a 45 × 30 cm aquarium footprint (medaka).
- Most Sulawesi ricefish: at least 45 L and 0.16 square metres of floor area; species over 60 mm need 120 L and 0.4 square metres (sulawesi).
- O. nigrimas needs open swimming space and a tank at least 80 cm long (sulawesi).
- For medaka provide dark substrate, dense plants, surface vegetation and open patches (medaka).
- Determine locality and salinity before setting up wild-origin fish (medaka).
Diet
- Suitably sized quality flakes or granules (medaka).
- Live/frozen Daphnia and Artemia (medaka).
- Finely chopped bloodworms (medaka).
Social life
- Medaka are more confident in groups of eight or more; separate Oryzias species for breeding because hybridization is possible (medaka).
Health watch
- Ammonia toxicity from inadequate biofiltration (fish_health).
- Parasitic skin and gill infections (fish_health).
- Nutritional deficiencies from unsuitable diets (fish_health).
Understanding the animal
About this animal
About this animal
This small (up to about 3.6 cm or 1.4 in) native of Japan is a denizen of rice paddies, marshes, ponds, slow-moving streams and tide pools. It is euryhaline, occurring in both brackish and freshwater.
Quoted from the Wikipedia article “Japanese rice fish” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater and brackish water, in rivers and streams, estuaries. Uses both the bottom and open water. Adults occur in ponds, marshes, paddy fields and small flows of plains. |
| Water it lives in | Freshwater / brackish water, 64–75 °F (18–24 °C), pH 7–8, hardness 9–19 dH. |
| Climate | Subtropical climate. |
| Behavior to plan for | Breeding: external brooders. |
What this means for care
- Keep water within its wild range, 64–75 °F.
- It tolerates or needs brackish water; check salinity needs before setup.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 84°F (up to 88°F in the hottest sampled areas) |
| Cool-season lows | about 27°F (down to 15°F in the coldest sampled areas) |
| Average temperature | 50–62°F across sampled records |
| Relative humidity | 69–74% on average (driest month about 63%) |
| Rainfall | about 1380 mm a year |
| Winters | Cool to cold winters (lows around 27°F) in much of its native range. Seasonal slowdown may be relevant, but species-specific biology determines whether brumation or hibernation occurs. |
Measured at 203 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The Japanese rice fish (Oryzias latipes), also known as the medaka, is a member of genus Oryzias (ricefish), the only genus in the subfamily Oryziinae. This small (up to about 3.6 cm) native of Japan is a denizen of rice paddies, marshes, ponds, slow-moving streams and tide pools. It is euryhaline, occurring in both brackish and freshwater. It became popular as an aquarium fish because of its hardiness and pleasant coloration: its coloration varies from creamy-white to yellowish in the wild to white, creamy-yellow, or orange in aquarium-bred individuals. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Reproduction | Carries eggs for some time before deposition. Oocytes mature at night followed by ovulation at dawn. — FishBase |
| Biology | Adults occur in ponds, marshes, paddy fields and small flows of plains. They prefer slow-moving streams. Inhabit mainly waters of lowlands and brackish water, and also known to inhabit tide pools of coasts of certain regions in Japan and Korea. — FishBase |
| History and naming | As originally defined, O. latipes was native to much of east and mainland southeast Asia, but in recent decades most of these populations have been split off as separate species based on morphological (morphometrics and meristics) and genetic evidence. This limits the native range of definite O. latipes to Japan: eastern and southern Honshu, Shikoku, Kyushu, and smaller southern islands in the country. — Wikipedia (community-edited) |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Maximum recorded lifespan
Longest recorded lifespan reported by each database; typical lifespans are usually shorter. The AnAge record comes from an animal in human care.
Adult length
Maximum recorded length. Measured as standard length (snout to the base of the tail, not counting the tail fin). Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Incubation
Minimum tank footprint
Seriously Fish recommends a tank base of at least 18 × 12 in (about 11 US gallons).
Veterinary & husbandry research
Veterinary & husbandry research
- A comparative genomic database of skeletogenesis genes: from fish to mammals Nie CH et al., Comparative biochemistry and physiology. Part D, Genomics & proteomics 2021
- Parental dietary seleno-L-methionine exposure and resultant offspring developmental toxicity Chernick M et al., Aquatic toxicology (Amsterdam, Netherlands) 2016
- Xmrk-induced melanoma progression is affected by Sdf1 signals through Cxcr7 Liedtke D et al., Pigment cell & melanoma research 2014
- Resolving mechanisms of toxicity while pursuing ecotoxicological relevance? Hinton DE et al., Marine pollution bulletin 2005
Peer-reviewed papers that mention this species alongside captivity, zoos, veterinary care or aquaculture. Some cover several species or mention it only in passing, so check the abstract. See all 92 on PubMed → 170
Sources for this sheet
- AnAge: The Animal Ageing and Longevity Database (Human Ageing Genomic Resources) Peer-reviewed researchCurated, referenced longevity and life-history records for thousands of species; maximum lifespans are often from zoo animals.
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Seriously Fish: Oryzias latipes Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Schwarzer et al. (2026): Sulawesi ricefish biology and aquarium husbandry, Bulletin of Fish Biology Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual: Disorders and Diseases of Fish Zoo, university or veterinaryAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual: Management of Aquarium Fish Zoo, university or veterinaryAdded in the 2026 source-checked care-guide review.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
- PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
