Identity and search names

Common name
Medaka ricefish
Scientific name
Oryzias latipes
Other names
Medaka, Japanese ricefish, Japanese killifish, Oryzias latipes
Category
Freshwater fish
Group
Rasboras, danios and minnows
Origin
Southern Japan and adjacent East Asian waters for O. latipes sensu stricto; domestic strains have a long captive history
Review outcome
PASSED

Environment and housing

Environment
Freshwater
Care level
Beginner to intermediate
Adult size
Usually 3–4 cm total length
Expected lifespan
About 2–4 years
Minimum housing
At least 90 L for a group of 10 or more, with a secure lid and seasonal temperature stability
Temperature
16–26 °C; avoid chronic high temperature
pH
6.5–8.0
Hardness or minerals
Moderately soft to hard
Salinity
Freshwater; slight natural salinity tolerance does not require routine salt
Lighting
Moderate with floating or fine-leaved spawning cover
Social structure
Keep at least 10 with a balanced sex ratio and dense refuge for subordinate fish
Placement or swimming zone
Surface and upper-middle water
Temperament
Peaceful, active and social
Compatibility
Use peaceful cool-tolerant fish; avoid large predators and permanently tropical high-temperature communities
Habitat structure
Planted aquarium or protected tub with calm margins, open surface, secure cover and refuge from temperature extremes

Feeding and nutrition

Diet
Tiny insects, crustaceans, zooplankton, algae-associated foods and fine prepared diets
Feeding frequency
Feed small varied portions once or twice daily and reduce waste during cool periods

Breeding and reproduction

Breeding or reproduction
Females briefly carry a cluster of fertilised eggs beneath the body before attaching them to fine plants or spawning mops. Collect mops or eggs to protect them from adults
Parental care
No care after eggs are attached; adults may consume eggs and fry

System demands

Filtration
Use mature biological filtration sized for the full adult group and feeding load, with intake protection where juveniles, long fins or small fish are present. Provide steady turnover without preventing normal swimming or resting.
Aeration
Maintain strong surface gas exchange and stable dissolved oxygen. Increase aeration during warm weather, medication, transport recovery, breeding crowding or any ammonia or nitrite event.
Maintenance
Test ammonia, nitrite and nitrate, remove waste from feeding and shelter zones, and perform regular temperature- and chemistry-matched water changes before nitrate or dissolved organics accumulate.

Detailed husbandry

Identity scope
This profile applies to Oryzias latipes sensu stricto and domestic medaka derived from the southern Japanese lineage. Northern Japanese fish are O. sakaizumii, while Chinese and western Korean lineages historically included under medaka may represent O. sinensis; domestic colour strains must not be assigned a wild locality without records.
Adult size and space
Usually 3–4 cm total length. At least 90 L for a group of 10 or more, with a secure lid and seasonal temperature stability. Plan around adult dimensions, activity, social structure, aggression and waste production rather than sale size.
Social structure
Keep at least 10 with a balanced sex ratio and dense refuge for subordinate fish
Placement or swimming zone
Primary zone: Surface and upper-middle water. Keep that zone usable for movement, feeding and refuge.
Feeding ecology
Tiny insects, crustaceans, zooplankton, algae-associated foods and fine prepared diets
Feeding plan
Feed small varied portions once or twice daily and reduce waste during cool periods
Water stability
Maintain 16–26 °C; avoid chronic high temperature; pH 6.5–8.0; hardness/minerals: Moderately soft to hard. Stable oxygenation and nitrogen-cycle control matter more than chasing one exact number.
Adult projected load
Plan capacity for Keep at least 10 with a balanced sex ratio and dense refuge for subordinate fish at the documented adult size (Usually 3–4 cm total length) in At least 90 L for a group of 10 or more, with a secure lid and seasonal temperature stability. Include feeding intensity, territorial behaviour and breeding growth rather than counting sale-size juveniles.
Filtration
Use mature biological filtration sized for the full adult group and feeding load, with intake protection where juveniles, long fins or small fish are present. Provide steady turnover without preventing normal swimming or resting.
Aeration
Maintain strong surface gas exchange and stable dissolved oxygen. Increase aeration during warm weather, medication, transport recovery, breeding crowding or any ammonia or nitrite event.
Maintenance
Test ammonia, nitrite and nitrate, remove waste from feeding and shelter zones, and perform regular temperature- and chemistry-matched water changes before nitrate or dissolved organics accumulate.
Habitat structure
Planted aquarium or protected tub with calm margins, open surface, secure cover and refuge from temperature extremes
Compatibility plan
Use peaceful cool-tolerant fish; avoid large predators and permanently tropical high-temperature communities
Breeding plan
Females briefly carry a cluster of fertilised eggs beneath the body before attaching them to fine plants or spawning mops. Collect mops or eggs to protect them from adults Parental care: No care after eggs are attached; adults may consume eggs and fry.
Quarantine
Quarantine new fish in a separate cycled aquarium with dedicated equipment. Match temperature and mineral chemistry gradually, confirm feeding and normal respiration, and never add transport water to the established aquarium.
Welfare checks
Maintain the stated adult space and social structure, verify feeding and intervene early when injury, exclusion, weight loss, abnormal respiration or altered behaviour appears. “Medaka” is not one undifferentiated wild lineage. Do not release domestic strains or label them as locality-pure without provenance.
Biosecurity and release
Never release fish, fry, eggs, aquarium water, sediment, plants or live foods into drains, dams or natural waterways. Confirm current Australian import conditions and South Australian possession, trade and movement rules before acquisition or transfer.
Main risk
“Medaka” is not one undifferentiated wild lineage. Do not release domestic strains or label them as locality-pure without provenance.
Overridable warnings
“Medaka” is not one undifferentiated wild lineage. Do not release domestic strains or label them as locality-pure without provenance. Any override must still preserve adult space, social welfare, stable chemistry, oxygen and filter capacity.

Welfare and risk

Welfare checks
Maintain the stated adult space and social structure, verify feeding and intervene early when injury, exclusion, weight loss, abnormal respiration or altered behaviour appears. “Medaka” is not one undifferentiated wild lineage. Do not release domestic strains or label them as locality-pure without provenance.
Main warning
“Medaka” is not one undifferentiated wild lineage. Do not release domestic strains or label them as locality-pure without provenance.
Biosecurity
Never release fish, fry, eggs, aquarium water, sediment, plants or live foods into drains, dams or natural waterways. Confirm current Australian import conditions and South Australian possession, trade and movement rules before acquisition or transfer.

Sources

Source note

Current identity or scope, husbandry, system-demand, welfare and Australian biosecurity evidence checked; active retired-source links removed; all AquaNexus wording is original.

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