Description
The harlequin rasbora (Trigonostigma heteromorpha) is a small Southeast Asian cyprinid, easily recognised by its coppery or pinkish body and the large triangular black marking across the rear flank. It is a peaceful, hardy species well suited to calm community aquariums.
Its behaviour improves when it is kept in a sizeable school with vegetation, shaded areas, and open mid-water swimming space. Its colours are usually more intense over a dark substrate and under moderate lighting.
Sexual dimorphism is subtle: adult females are generally slightly larger and rounder, while males tend to be slimmer and may show stronger colour. The shape of the black marking can provide a clue, but it is not always a completely reliable way to determine sex.
Behavior
This social species should be kept in a group of at least 8. A school of 10–12 or more feels more secure and displays more natural interactions. Although the fish may move in close coordination when startled or exploring, under calm conditions they usually form a looser shoal.
Harlequin rasboras mainly occupy the middle water levels and can live with other small, peaceful fish that share similar requirements. Avoid aggressive, much larger, or overly boisterous tank mates. The ideal layout combines dense planting around the sides and rear, shaded retreats, and a clear central area for swimming.
Habitat
Trigonostigma heteromorpha occurs across the Malay Peninsula, Singapore, and Sumatra. It inhabits forest streams, swampy areas, and quiet waterways, often shaded by riparian vegetation and containing roots, branches, and leaf litter.
These waters are generally soft and acidic and may be stained brown by tannins, although captive-bred fish tolerate some variation when conditions remain stable. In the aquarium they benefit from gentle flow, abundant planting, moderate lighting, and regular water changes. Avoid sudden shifts in temperature or water chemistry.
El pez Rasbora Arlequín es una especie de cardumen, lo que significa que, de forma natural, vive y se desplaza en grupos numerosos y coordinados.
Se recomienda mantener un mínimo de 8 individuos para que se sientan cómodos y reducir su nivel de estrés.
Habitats
Fish sharing this habitat
Estos peces aparecen en uno o mas habitats asociados a esta ficha. No implica compatibilidad directa en acuario.
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
Unlike many cyprinids that scatter their eggs, harlequin rasboras usually attach them to the underside of broad leaves. During courtship the pair turns upside down beneath a leaf to spawn. There is no parental care, and the adults may eat the eggs or fry.
For controlled breeding, use a separate, dimly lit tank with sponge filtration, very soft, slightly acidic water, and broad-leaved plants such as Cryptocoryne. Introduce a well-conditioned pair and remove them after spawning. The eggs generally hatch in about one or two days; once the fry become free-swimming they require infusoria or a suitable liquid fry food, followed by microworms and newly hatched Artemia.
Diet
This omnivorous species readily accepts quality prepared foods. Use fine flakes or appropriately sized micro-pellets as the staple and supplement them with small live or frozen foods such as Artemia, daphnia, Cyclops, and mosquito larvae.
Offer one or two small portions per day, only as much as the school can consume within a few minutes. Rotating different foods supports good condition and colour. Check that every fish is feeding when they share the aquarium with faster or more assertive species.
What about your tank?
Enter your tank's values to see only the compatible species that fit them. Litres apply to fish.
Compatible fish
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6–7 and 24–26 °C.
They share water: pH 5.5–7 and 22–26 °C.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6–7 and 22–25 °C.
They share water: pH 6.5–7 and 22–24 °C.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 6–7 and 25–26 °C.
They share water: pH 6–7 and 24–26 °C.
They share water: pH 5.5–7 and 22–26 °C.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 5.5–7 and 26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 5.5–6.5 and 24–26 °C.
They share water: pH 5.5–7 and 23–26 °C.
They share water: pH 5.5–7 and 23–26 °C.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
Compatible invertebrates
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 5.5–6.5 and 22–24 °C.
They share water: pH 7 and 22–25 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 5.8–6.8 and 22–24 °C.
They share water: pH 5.8–6.8 and 22–24 °C.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 6.5–7 and 22–26 °C.
They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
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They share water: pH 7 and 22–26 °C. They only meet at the very edge, so the tank has to hold that value.
Sources
- FishBaseFroese y Pauly (eds.), 2026. FishBase.
- Tan (2020)Trigonostigma truncata, a new species of harlequin rasbora. Raffles Bulletin of Zoology, 68: 421–433.
Plan your next aquarium
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