Truncate harlequin rasbora
Separated from the harlequin rasbora only in 2015, and the largest of the group — the black wedge is squarer at the front and the fish is noticeably deeper-bodied. Most tanks sold a mixed group of harlequins contain some of these.
Quick profile
- Scientific name
- Trigonostigma truncata
- Adult size
- 4–5.5 cm (1.6–2.2 in)
- Lifespan
- 4–6 years
- Temperature
- 23–28 °C (73–82 °F)
- pH
- 5–7
- Hardness
- 1–10 °dGH
- Minimum tank
- 75 L (20 US gal)
- Minimum length
- 60 cm
- Swimming zone
- Midwater
- Social
- Schooling — at least 8
- Diet
- Micropredator
- Overall confidence
- low confidence
What keeping this species involves
Hardy once settled and better in soft acidic water than the general community advice for harlequins suggests.
Peat swamp forest streams and shaded blackwater channels.
Identity and names
- Common name
- Truncate harlequin rasbora
- Scientific name
- Trigonostigma truncata
- Family
- Danionidae
- Order
- Cypriniformes
- Class
- Actinopterygii
- Also sold as
- Trigonostigma truncata, large harlequin rasbora
Adult size and growth
4–5.5 cm (1.6–2.2 in)
Typical lifespan in an aquarium: 4–6 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.
Water and tank requirements
A shoal of deeper-bodied rasboras needs continuous horizontal swimming space.
Why these ranges: Peat swamp water, soft and acidic. The band is the habitat and it matters more here than for the harlequin, because this species is more consistently a blackwater animal.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 23–28 °C (73–82 °F) | Stability matters more than hitting an exact figure. |
| pH | 5–7 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 1–10 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 75 L (20 US gal) | A floor, not a recommendation. |
| Minimum footprint | 60 cm long | A shoal of deeper-bodied rasboras needs continuous horizontal swimming space. |
| Water flow | low | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Leaf litter, driftwood, shade and dark substrate. |
Behaviour
- Holds mid-depth in a loose formation that tightens the moment anything passes the glass.
- Colour deepens markedly over dark substrate in tannin-stained water.
Telling males from females
Males have a more sharply angled front edge to the wedge; females are deeper through the belly.
Feeding
- Diet type
- Micropredator
- Staples
- Small dry foods, Frozen daphnia and cyclops, Baby brine shrimp
Breeding
- Strategy
- Eggs placed singly on the undersides of broad leaves over several days
- Difficulty
- challenging
- 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.
- Sold as harlequin rasbora and mixed with the other two Trigonostigma, which produces a group that never schools as one.
- Its peat swamp habitat is being drained across much of its range.
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
- Malay Peninsula and Sumatra
- Habitat
- Peat swamp forest streams and shaded blackwater channels.
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 | Trigonostigma truncata | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Malay Peninsula and Sumatra | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 4–5.5 cm | Aquarium-literature consensus | low confidence | AquariumHQ husbandry synthesis |
| lifespan | 4–6 years | Aquarium-literature consensus | low confidence | AquariumHQ husbandry synthesis |
| temperature | 23–28 °C | Aquarium-literature consensus | low confidence | AquariumHQ husbandry synthesis |
| ph | 5–7 pH | Aquarium-literature consensus | low confidence | AquariumHQ husbandry synthesis |
| general hardness | 1–10 °dGH | Aquarium-literature consensus | low confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 75 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 60 cm | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum group size | ≥ 8 | AquariumHQ editorial position | low 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 2026-08-13. 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 checkableLimited evidence — treat with caution.
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. No checklist distribution statement is held for this species. The range on the page is editorial until one is.
What would improve this: Go and read a source. This is reachable and has not been reached.
adult sizeAquariumHQ'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: size a well-kept specimen reaches — 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.
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.
Group size and social behaviour
Schools loosely once settled and tightly when startled. Mixed groups of the three Trigonostigma do not school together properly.