Harlequin Rasbora Care Guide - Aquarium Setup, Diet & Breeding

The Harlequin Rasbora is a small, elegant schooling fish with a coppery-pink to orange body and a distinctive dark, wedge-shaped patch extending from the middle of the body toward the tail. Its metallic colour becomes especially attractive when the fish are relaxed and moving together in a planted aquarium. Clear fins and a dark-edged tail complete its neat, streamlined appearance.

These rasboras are peaceful, active and naturally social. A group spends much of its time cruising through the middle and upper levels of the aquarium, often turning in unison before settling among plants. They are generally confident when kept in a suitably sized shoal, while small groups can become shy and display less natural behaviour.

In the wild, Harlequin Rasboras inhabit calm or gently flowing waters beneath dense tropical vegetation. Many populations come from tannin-stained environments where fallen leaves, branches and peat-darkened water create a subdued, sheltered setting. Their coloration provides an attractive contrast against this darker background.

Trigonostigma heteromorpha has long been one of the most popular community aquarium fish because it combines vivid markings with a calm temperament and modest adult size. It is an excellent choice for peaceful planted aquariums and works particularly well as part of a mixed Southeast Asian-inspired community.

Harlequin Rasboras are native to Southeast Asia, occurring across the Malay Peninsula, southern Thailand, Singapore and parts of Sumatra. They are associated with slow-moving forest streams, peat swamps and blackwater habitats rich in leaf litter and submerged vegetation.

A group should have at least a 60-litre aquarium, with a footprint around 60 cm long by 30 cm wide; a longer tank is preferable because it provides more swimming room. Use dense planting around the edges, open space through the centre, and driftwood, roots or leaf litter to create cover and a natural Southeast Asian stream feel. A dark, fine-grained substrate, gentle filtration and subdued lighting help the fish feel secure, while floating plants can provide useful shade. Leave some uninterrupted swimming space and use a secure lid, as rasboras can jump when startled.

Harlequin Rasboras reach a maximum adult length of about 5 cm (2 inches). Females are typically slightly larger and deeper-bodied than males, although individual size varies.

Harlequin Rasboras are omnivores that benefit from a varied diet of high-quality small flakes or micro-pellets supplemented with frozen or live foods such as daphnia, brine shrimp, mosquito larvae and bloodworms. Feed small portions that they can finish quickly, and offer appropriately sized foods because their mouths are small. Occasional live foods can help bring out their colour and provide useful conditioning for breeding.

Harlequin Rasboras are peaceful community fish and can be kept with other small, non-aggressive species such as neon and ember tetras, smaller danios, celestial pearl danios, honey gouramis, peaceful dwarf corydoras and kuhli loaches. They also mix well with other gentle rasboras when the aquarium is spacious enough. Avoid large, predatory or fin-nipping fish, including angelfish, aggressive barbs and many larger cichlids, which may harass or eat them.

Harlequin Rasboras are egg-scattering fish that deposit their eggs on the underside of broad-leaved plants. Condition a group with live or frozen foods, then provide soft, slightly acidic water and fine-leaved or broad plants such as Cryptocoryne. Spawning often takes place in the early morning, after which the adults should be removed because they may eat the eggs. Eggs usually hatch within roughly 24 to 36 hours, and the tiny fry initially need infusoria or another suitably fine first food before progressing to baby brine shrimp.

Females are usually fuller through the abdomen and slightly larger overall, particularly when carrying eggs. Males tend to be slimmer, with a more sharply defined lower edge to the dark body wedge and often somewhat stronger colouration.