Harlequin Rasbora Colour Varieties: Classic, Purple and Black

Most aquarists know the harlequin rasbora from the classic copper-orange body and distinctive black triangular patch, but the genus Trigonostigma contains several recognised species — each with distinct colouration — that are collectively sold under the “harlequin rasbora” umbrella. Understanding the harlequin rasbora colour varieties helps you make a deliberate choice for your aquascape rather than picking blindly from a shop tank. Gensou Aquascaping at Everton Park, Singapore carries all three commonly available forms, and this guide covers what sets each apart.

The Classic Harlequin: Trigonostigma heteromorpha

Trigonostigma heteromorpha is the original — the fish that made this genus famous. Body colouration is a warm copper-orange to rose-gold, and the black patch runs from roughly mid-body to the tail base in a roughly triangular shape. The patch has a distinctive curved lower border that differentiates it immediately from other forms. Adults reach 4–5 cm. Under warm, slightly tinted water with good lighting, the copper colouration intensifies noticeably. This remains the most widely available form in Singapore shops and is priced at roughly $1.50–2.50 per fish.

The Purple Harlequin: Trigonostigma heteromorpha “Purpurea”

The purple harlequin is not a separate species but rather a colour variant of T. heteromorpha, distinguished by a deeper violet-purple body tone in place of the standard copper-orange. Under neutral white light the difference can appear subtle, but under warm-spectrum or planted tank lighting the purple cast becomes unmistakable. The black triangle is present but often appears slightly softer at its edges. Some sources suggest the purple form is wild-caught from specific river drainages in Southeast Asia; others indicate it may be a line-bred variant. Either way, care requirements are identical to the classic form.

The Black Harlequin: Trigonostigma heteromorpha “Black”

The black harlequin — sometimes called the dark or melanistic form — carries a significantly expanded black marking that covers most of the body rather than just the posterior triangle. In some specimens the black nearly swallows the copper base colouration entirely, leaving only a narrow gold margin along the upper body. This is the least commonly available form in Singapore and commands a premium: expect to pay $3–5 per fish from specialist importers. Under LED lighting with a heavy red spectrum, residual gold colouration becomes more visible and the fish takes on a striking two-tone appearance.

Lambchop Rasbora: Often Confused

Trigonostigma espei — the lambchop rasbora — is sometimes sold alongside harlequins and confused with the classic form. The key difference is the black marking’s shape: in T. espei it is narrower, more elongated, and tapers to a point at the front — resembling a lambchop cut rather than a triangle. Body colouration is warmer and more orange than the classic harlequin. Size is also smaller, typically 3–3.5 cm versus the classic’s 4–5 cm. Lambchops are slightly more active and prefer slightly warmer temperatures, ideally 26–28°C.

Care Requirements Across All Forms

All Trigonostigma harlequins share nearly identical care requirements. Temperature 24–28°C, pH 6.0–7.0, GH 2–8 — all within comfortable range using treated Singapore tap water. They are shoaling fish; fewer than eight individuals produces shyness and suppressed colouration. A shoal of 15–20 will school tightly and display constantly, which is where the real beauty lies. Plant the tank densely, particularly with broad-leaved species at mid-level such as Cryptocoryne wendtii, as harlequins use these for shade and resting positions.

Breeding Across Colour Forms

All three colour forms breed in the same manner — the female presses her belly against the underside of a broad leaf and releases eggs while the male embraces her. Cryptocoryne leaves are the classic spawning site in the aquarium, though java fern and Anubias are also used. Eggs hatch in 24–36 hours and fry become free-swimming on day three or four. If keeping multiple colour varieties, be aware that cross-spawning between forms will occur freely in a community tank — managing pure colour lines requires species-only breeding setups.

Choosing Between Varieties for Your Tank

The classic form suits virtually any planted community and is the most forgiving of water conditions. The purple variety creates a more unusual, cooler colour palette — it pairs beautifully with blue and green aquascape plants rather than the red-orange palette the classic complements. The black harlequin makes the strongest visual statement in contrast-heavy aquascapes with pale substrate or white hardscape. Whichever form you choose, a large shoal in a well-planted tank is one of Singapore’s most reliably rewarding aquarium fish.

Related Reading

• How to Breed Harlequin Rasboras: Under-Leaf Spawners
• Harlequin Rasbora vs Lambchop Rasbora: Spot the Difference
• Mystery Snail Colour Varieties: Gold, Blue, Magenta and Ivory
• Ricefish Medaka Colour Varieties: Platinum, Orange and Lame Scale
• White Cloud Mountain Minnow Colour Varieties: Gold, Long-Fin and Meteor