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title: "Harlequin Rasbora: The Complete Care, Tank & Breeding Guide" description: "The definitive harlequin rasbora (Trigonostigma heteromorpha) care guide: water parameters, tank setup, shoaling, feeding, the unusual leaf-underside breeding, and tank mates." slug: harlequin-rasbora commonName: Harlequin Rasbora scientificName: Trigonostigma heteromorpha family: Danionidae order: Cypriniformes difficulty: Beginner minTankSize: 15 temperature: "72–80°F (22–27°C)" ph: "6.0–7.5" hardness: "2–12 dGH" lifespan: "4–6 years" maxSize: "2 inches (5 cm)" origin: "Malaysia, Thailand, Sumatra, Singapore" publishedAt: "2026-06-04"

Harlequin Rasbora: The Complete Care, Tank & Breeding Guide

The harlequin rasbora is one of the great community-tank classics — a hardy, peaceful, copper-and-black shoaling fish that has graced planted aquariums for the better part of a century. Trigonostigma heteromorpha pairs the easygoing, beginner-proof temperament of the best community fish with a genuinely beautiful look: a warm copper-orange body marked by a bold black "Lambada" triangle on the rear half, multiplied into a glowing shoal. It's forgiving enough for a first tank yet rewarding enough to keep any aquarist happy, and it has one of the most unusual breeding behaviours of any small fish.

This guide is the complete reference: the harlequin's biology, how to set up its tank, what to feed it, its peaceful shoaling behaviour, the remarkable leaf-underside spawning, and which tank mates suit it.

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Species Overview

The harlequin rasbora (Trigonostigma heteromorpha, formerly Rasbora heteromorpha) is a small cyprinid from Southeast Asia, reaching about 5 cm (2 inches). Its body is a warm copper to pinkish-orange, marked by a distinctive solid black triangle (the "Lambada" or "pork-chop" patch) covering the rear half of the body — a clean, instantly recognisable pattern that's beautiful in a shoal. There are also similar species sold as harlequins (the lambchop and glowlight rasboras, T. espei and T. hengeli), cared for identically.

The harlequin is peaceful, hardy, adaptable, and long-lived (4–6 years), making it one of the best community fish for beginners and a long-standing hobby staple. It's a true shoaling fish that's confident and colourful in a group, and it's gentle enough for community and even some nano setups. Its combination of beauty, hardiness, peacefulness, and an unusual, achievable breeding behaviour makes it a perennial favourite.

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Natural History and Origin

Trigonostigma heteromorpha is native to Malaysia, Thailand, Sumatra, and Singapore, living in soft, acidic, peat-stained blackwater streams and swamp forests shaded by overhanging vegetation — warm, gently flowing, tannin-rich water over leaf litter. This soft, warm, dim habitat is where it shows its best colour, though decades of tank breeding have made it adaptable to a wide range of conditions.

In the wild, harlequins shoal among submerged plants and roots, feeding on tiny invertebrates, and they spawn in a remarkable way: rather than scattering eggs, the female deposits them on the underside of broad leaves while inverted, a distinctive behaviour shared by its genus. Their natural blackwater origin means soft, slightly acidic, planted, gently-tannin-stained aquarium water brings out their richest copper colour, though they tolerate harder, neutral water well thanks to generations of captive breeding.

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Water Parameters

Harlequin rasboras are hardy and adaptable, doing well across a range of conditions, which is a big part of their beginner appeal. They show their best copper colour in soft, slightly acidic, gently tannin-stained water but thrive in most stable, cycled community tanks. Confirm cycling with the nitrogen cycle tracker and check values with the water parameters reference; botanicals and driftwood deepen their colour if you want the blackwater look.

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Tank Setup Guide

Tank size

A shoal of 8–10 harlequins is comfortable in a 15-gallon (57-litre) tank, with 20+ gallons better for a larger group or a community. They're peaceful and modestly sized, suiting many community and larger nano setups.

Aquascape — planted with the blackwater touch

Harlequins shine in a planted tank with some open swimming space for shoaling. A dark substrate, driftwood, broad-leaved plants (which they may use for spawning), Java moss, and leaf litter/botanicals for gentle tannins all enhance their copper colour and recreate their habitat. Subdued lighting (or floating plants like duckweed) intensifies their colour and keeps them confident, though they're far less light-shy than blackwater specialists.

Filtration, flow, lighting

Use reliable filtration with gentle-to-moderate flow and moderate lighting. A planted, stable, gently-tannin-stained tank brings out their best colour, but they're forgiving of a standard community setup — part of why they're such a reliable beginner fish.

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Feeding Guide

Harlequin rasboras are omnivores with small mouths that take a wide variety of foods.

What to feed

• Quality micro-pellets and crushed flake — a convenient staple.
• Live and frozen daphnia and baby brine shrimp — relished, excellent for colour and conditioning.
• Cyclops, microworms, and small frozen foods for variety.

How often

Feed two to three small meals daily. Harlequins feed readily and aren't easily outcompeted, but ensure small foods so they can manage them. A varied diet with regular small live/frozen foods deepens their warm copper colour. A healthy harlequin is well-coloured, active, and shoals confidently in the open.

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Behavior and Temperament

Harlequin rasboras are peaceful, active shoaling fish that feel secure and look their best in a group of 8 or more, drifting and foraging together through the planted tank. In small numbers they become shy and washed-out, so a proper shoal is important. They're confident, undemanding, and completely peaceful toward other species, making them superb dither fish and ideal community citizens.

They occupy the middle-to-upper water column, adding gentle movement and warm colour, and quickly learn feeding routines. There's no aggression to manage — harlequins are the definition of an easy, harmonious community fish. Their hardiness, peacefulness, and long history in the hobby make them one of the most reliable shoaling fish you can keep.

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Compatibility

Harlequin rasboras are excellent peaceful community fish, compatible with a very wide range of gentle tank mates.

Good tank mates: neon tetra, cardinal tetra, ember tetra, rummynose tetra, corydoras, otocinclus, dwarf gourami, honey gourami, pearl gourami, bolivian ram, kuhli loach, betta fish (peaceful individuals), and cherry shrimp (adults).

Cautions:

• Large or predatory fish — may eat the small harlequins.
• Aggressive or fin-nipping fish — stress the peaceful shoal.

There are very few fish a harlequin rasbora can't get along with, short of those big enough to eat it. Use the compatibility checker to plan a harmonious community — a harlequin shoal with a gourami centerpiece and corydoras is a timeless, beginner-friendly setup.

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Breeding Guide

Harlequin rasboras have one of the most distinctive and achievable breeding behaviours among small fish — they don't scatter eggs, they deposit them on the underside of broad leaves.

Sexing is subtle: males are slightly slimmer and more intensely coloured, with a slightly differently-shaped black triangle (the leading edge often more rounded/extended at the bottom); females are a touch rounder and fuller. Conditioning a group on rich foods helps.

For breeding, provide soft, acidic, warm water (this is important — hard water often prevents fertile spawns) and broad-leaved plants (such as cryptocoryne or anubias) as spawning sites. A pair courts beneath a chosen leaf, and the female turns upside-down to lay her eggs on the underside of the leaf, the male fertilising them — a fascinating spawning posture unique to the genus. The pair may repeat this on several leaves. Remove the adults after spawning, as they eat the eggs. The eggs hatch in about a day, and the fry become free-swimming after a few more days, reared on infusoria and then microworms and baby brine shrimp. Soft water and broad leaves are the keys; it's a rewarding and unusual spawn to witness.

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Health and Disease

Harlequin rasboras are hardy, and disease is uncommon with good care.

Ich can follow temperature swings or stress; treat promptly. Bacterial and fungal infections follow poor water or stress. As shoaling fish, they're stressed by being kept in too-small a group, which can undermine their health and colour. Newly added fish may be pale until settled.

Prevention: a stable, cycled, planted tank with good water quality, a proper shoal, gentle flow, small varied foods, peaceful tank mates, and quarantine of new arrivals. Given their renowned hardiness, harlequins are one of the most trouble-free community fish in the hobby — a big reason they've remained popular for generations.

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Interesting Facts

• Upside-down egg-layers. Females spawn by inverting and depositing eggs on the underside of broad leaves — a distinctive behaviour unique to the genus, unlike the egg-scattering of most small fish.
• A hobby classic. Harlequins have been a community-tank staple for the better part of a century, prized for hardiness and beauty.
• The "Lambada" patch. The bold black triangle on the rear body is the species' signature, also likened to a pork chop.
• A genus of look-alikes. The lambchop (T. espei) and glowlight (T. hengeli) rasboras are close relatives sold and cared for the same way.
• Blackwater roots. From soft, peat-stained Southeast Asian streams, they show their richest copper in soft, tannin-stained water.

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Bringing It Together

The harlequin rasbora is one of the best community fish you can keep — hardy, peaceful, beautiful, adaptable, and long-lived, with a warm copper glow that lights up a planted tank when kept in a proper shoal. Give it a 15-gallon-plus planted tank, stable water (soft and slightly acidic for the best colour, but adaptable to most conditions), gentle flow, small varied foods, and peaceful tank mates — and keep a group of 8 or more — and it will shoal confidently and colourfully for years, very possibly treating you to its remarkable upside-down, leaf-underside spawning. It pairs perfectly with a honey or pearl gourami centerpiece, corydoras, and other peaceful community fish. Plan the build with the AI Tank Blueprint generator and the compatibility checker.