Home / Fishes / Ricefish, halfbeaks, needlefish / Javanese ricefish
No federal permit to keepJavanese ricefish
Oryzias javanicus
Fishes › Ricefish, halfbeaks, needlefish (Beloniformes) › Adrianichthyidae (Ricefish and medaka)
Oryzias javanicus, the Javan ricefish or Javanese ricefish, is a small species of fish in the family Adrianichthyidae.
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 1.2 in / 3 cm; the largest recorded was 1.8 in).
- Water: Freshwater (tolerates brackish).
- Temperature: 72–77°F (range recorded for this species).
- pH: 7.5–8.5.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: A predator: feed meaty foods sized to its mouth (frozen fish, shrimp, worms); it will eat tankmates that fit in its mouth. FishBase classes it as a carnivore.
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, 75–84 °F, pH 7–9, 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: “This species has no special requirements in terms of décor though it tends to be less colurful when maintained in a sparsely-decorated set-up.”
- Diet: “A micropredator feeding on small insects, worms, crustaceans and other zooplankton in nature.”
- Tankmates: “Generally peaceful but does not make an ideal addition to many communities due to its small size.”
- 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
It lives in Peninsular Thailand, Peninsular Malaysia, Singapore, and Indonesia (Java, Sumatra, Borneo, Sulawesi, Bali and Lombok), where it can be seen in both brackish and fresh water in ponds, ditches, mangrove, swamps, streams and canals. It can grow to 4.5 cm (1.8 in) in total length.
Quoted from the Wikipedia article “Oryzias javanicus” (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. Uses both the bottom and open water. Found in ditches, canals, ponds. Occurs at the surface in habitats with dense growth of aquatic plants. Feeds on small crustaceans, insects and protozoans. |
| Water it lives in | Freshwater / brackish water, 72–77 °F (22–25 °C), pH 7.5–8.5. |
| Climate | Tropical climate. |
| Wild diet | Hunting macrofauna (predator). |
| Behavior to plan for | Breeding: external brooders. |
What this means for care
- Keep water within its wild range, 72–77 °F.
- It tolerates or needs brackish water; check salinity needs before setup.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 89°F (up to 93°F in the hottest sampled areas) |
| Cool-season lows | about 71°F (down to 67°F in the coldest sampled areas) |
| Average temperature | 77–82°F across sampled records |
| Relative humidity | 79–84% on average (driest month about 75%) |
| Rainfall | about 2386 mm a year |
Measured at 50 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 | Oryzias javanicus, the Javan ricefish or Javanese ricefish, is a small species of fish in the family Adrianichthyidae. It lives in Peninsular Thailand, Peninsular Malaysia, Singapore, and Indonesia (Java, Sumatra, Borneo, Sulawesi, Bali and Lombok), where it can be seen in both brackish and fresh water in ponds, ditches, mangrove, swamps, streams and canals. It can grow to 4.5 cm in total length. — 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 | Female carries her eggs outside her body in a cluster, attached to the genital pore by filaments. — FishBase |
| Biology | Found in ditches, canals, ponds. Occurs at the surface in habitats with dense growth of aquatic plants. Feeds on small crustaceans, insects and protozoans. — FishBase |
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.
Adult length
Common length to maximum recorded length. Measured as total length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Water hardness
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
- Negligible additive effect of environmental concentrations of fragmented polyethylene terephthalate microplastics on the growth and reproductive performance of Java medaka exposed to 17β-estradiol and bisphenol A Nam SE et al., Aquatic toxicology (Amsterdam, Netherlands) 2024
- Genome Sequence of the Euryhaline Javafish Medaka, Oryzias javanicus: A Small Aquarium Fish Model for Studies on Adaptation to Salinity Takehana Y et al., G3 (Bethesda, Md.) 2020
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. 170
Sources for this sheet
- 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.
