Common Harlequin Rasbora

Overview

The classic, wild-type form with a warm copper-orange body and the characteristic large triangular black patch on the rear half.

Appearance

Shared with the species: Harlequin Rasbora

Harlequin rasboras reach approximately 4–5 cm (1.6–2 in) in total length. The body has a warm copper-orange to rose-pink base color, and the defining feature is a large, roughly triangular black marking covering the rear half of the body, tapering to a point near the caudal peduncle—a pattern strikingly reminiscent of the diamond-patterned costume of a harlequin. The dorsal, anal, pelvic, and caudal fins carry a reddish tint. Males can be distinguished by a slightly larger and more curved black patch with a rounded lower edge near the anal fin, while females have a straighter lower edge and a fuller abdomen when gravid.

Care

Shared with the species: Harlequin Rasbora

Harlequin rasboras thrive in aquariums of at least 60–80 liters (15–20 gallons) and should always be kept in groups of a minimum of 6, with groups of 10–15 strongly preferred for natural schooling behavior. Water temperature should be 22–27°C (72–81°F) with a pH of 6.0–7.5 and soft to moderately hard water (0–12 dGH). To bring out their best colors and behavior, aquariums should include dense planting, a dark substrate, driftwood, and leaf litter to replicate their blackwater forest stream habitat. Low to moderate lighting and gentle filtration are ideal.

Feeding

Shared with the species: Harlequin Rasbora

In their natural environment, harlequin rasboras are micropredators feeding on small insects, zooplankton, daphnia, mosquito larvae, and other tiny invertebrates. In captivity they readily accept high-quality micro-pellets, small flake food, and are particularly enthusiastic about frozen or live foods including daphnia, baby brine shrimp, mosquito larvae, cyclops, and micro-worms. A varied diet that regularly includes live or frozen protein sources enhances coloration and encourages breeding condition.

Compatibility

Shared with the species: Harlequin Rasbora

Harlequin rasboras are completely peaceful and are among the best schooling fish for a community aquarium. They coexist harmoniously with virtually all similarly-sized, non-aggressive species: small tetras, other rasboras, danios, small barbs, corydoras and otocinclus catfish, dwarf cichlids such as apistogrammas and rams, and peaceful livebearers. Their schooling behavior is most impressive in groups of 10 or more.

Breeding

Shared with the species: Harlequin Rasbora

Breeding harlequin rasboras in captivity requires specific conditions. A separate, shallow breeding tank with very soft, acidic water (pH 5.5–6.5, dH below 4) at approximately 28°C should be set up with broad-leaved plants such as Cryptocoryne. In a unique spawning behavior, the female adopts an inverted position beneath a leaf, and the male wraps his tail around her body in a trembling embrace to release milt as she deposits adhesive eggs onto the underside of the leaf. A well-conditioned pair may deposit 80–300 eggs over several hours. Parents must be removed after spawning as they will consume the eggs.

Fun facts

Shared with the species: Harlequin Rasbora

The harlequin rasbora's triangular black patch may function as an intraspecific recognition signal—helping fish identify conspecifics in the dark, tannin-stained peat swamp waters where visual contrast between similarly-shaped species is minimal. Despite being naturally found in extremely acidic, ultra-soft blackwater (pH sometimes below 4.0), the species has proven to be one of the hardiest and most adaptable rasboras in captivity. The two closest relatives—Trigonostigma espei (the lambchop rasbora) and Trigonostigma hengeli—were originally described as subspecies but elevated to full species status and are occasionally seen in the trade.