Identity and search names
- Common name
- Harlequin rasbora
- Scientific name
- Trigonostigma heteromorpha
- Other names
- Rasbora heteromorpha, Harlequin fish
- Category
- Freshwater fish
- Group
- Rasboras, danios and minnows
- Origin
- Peat-swamp, forest-stream and associated lowland waters of the Malay Peninsula, southern Thailand and Sumatra
- Review outcome
- PASSED
Environment and housing
- Environment
- Freshwater
- Care level
- Beginner to intermediate
- Adult size
- Usually 4–5 cm total length
- Expected lifespan
- About 5–8 years
- Minimum housing
- At least 90 L with an 80 cm or longer swimming length
- Temperature
- 22–27 °C
- pH
- 4.0–7.5
- Hardness or minerals
- Very soft to moderately hard
- Salinity
- Freshwater; do not add salt routinely
- Lighting
- Subdued to moderate lighting with shaded plant cover
- Social structure
- Keep at least 10–12 in a stable school
- Placement or swimming zone
- Middle and upper water
- Temperament
- Peaceful, active and strongly schooling
- Compatibility
- Use peaceful community fish that tolerate the same warm, often soft-water conditions; avoid fin-nippers and large predators
- Habitat structure
- A mature aquarium with dark substrate, plants or wood at the margins, open mid-water swimming space and stable filtration
Feeding and nutrition
- Diet
- Small aquatic and terrestrial invertebrates plus fine quality prepared foods
- Feeding frequency
- Feed small varied portions once or twice daily and ensure timid fish are not displaced
Breeding and reproduction
- Breeding or reproduction
- Pairs turn beneath broad leaves and attach eggs to the underside; adults provide no care and may eat eggs or fry
- Parental care
- No parental care
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 Trigonostigma heteromorpha. Similar-looking T. espei and T. hengeli are separate species and must not be merged by colour or trade name.
- Adult size and space
- Usually 4–5 cm total length. At least 90 L with an 80 cm or longer swimming length. Plan around adult dimensions, activity, social structure, aggression and waste production rather than sale size.
- Social structure
- Keep at least 10–12 in a stable school
- Placement or swimming zone
- Primary zone: Middle and upper water. Keep that zone usable for movement, feeding and refuge.
- Feeding ecology
- Small aquatic and terrestrial invertebrates plus fine quality prepared foods
- Feeding plan
- Feed small varied portions once or twice daily and ensure timid fish are not displaced
- Water stability
- Maintain 22–27 °C; pH 4.0–7.5; hardness/minerals: Very soft to moderately hard. Stable oxygenation and nitrogen-cycle control matter more than chasing one exact number.
- Adult projected load
- Plan capacity for Keep at least 10–12 in a stable school at the documented adult size (Usually 4–5 cm total length) in At least 90 L with an 80 cm or longer swimming length. 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
- A mature aquarium with dark substrate, plants or wood at the margins, open mid-water swimming space and stable filtration
- Compatibility plan
- Use peaceful community fish that tolerate the same warm, often soft-water conditions; avoid fin-nippers and large predators
- Breeding plan
- Pairs turn beneath broad leaves and attach eggs to the underside; adults provide no care and may eat eggs or fry Parental care: No parental care.
- 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. A trio is not a school. Small groups lose normal behaviour and are more easily intimidated or stressed.
- 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
- A trio is not a school. Small groups lose normal behaviour and are more easily intimidated or stressed.
- Overridable warnings
- A trio is not a school. Small groups lose normal behaviour and are more easily intimidated or stressed. 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. A trio is not a school. Small groups lose normal behaviour and are more easily intimidated or stressed.
- Main warning
- A trio is not a school. Small groups lose normal behaviour and are more easily intimidated or stressed.
- 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.
- Eschmeyer’s Catalog of Fishes — Trigonostigma heteromorpha — Current accepted-name, synonym, family and habitat check
- Eschmeyer’s Catalog of Fishes — Trigonostigma heteromorpha — Accepted-name, synonym and taxonomic-placement cross-check
- Seriously Fish — Trigonostigma heteromorpha — Habitat, schooling, adult scale and underside-of-leaf spawning cross-check
- IUCN Red List search — Trigonostigma heteromorpha — Conservation-status and wild-provenance cross-check
- PIRSA — South Australian noxious fish list — Current South Australian possession and trade restriction cross-check
- DAFF — importing live ornamental fish to Australia — Current Australian live-fish import pathway and permitted-species warning