Harlequin Rasbora: The Jewel of Peaceful Planted Tanks

In the world of freshwater community fish, the Harlequin Rasbora is a classic favorite — and for good reason. With its shimmering copper body and distinctive black wedge, this tiny fish is not only eye-catching but also peaceful, hardy, and full of personality.

Perfect for beginners and adored by experienced aquarists, Harlequin Rasboras add motion, elegance, and harmony to any planted aquarium.

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Quick Overview

• Scientific Name: Trigonostigma heteromorpha

• Common Name: Harlequin Rasbora

• Origin: Southeast Asia (Thailand, Malaysia, Singapore, Sumatra)

• Size: 1.5–2 inches (3.5–5 cm)

• Lifespan: 5–8 years

• Temperament: Peaceful, social

• Tank Level: Mid to upper

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Appearance: Small But Striking

The Harlequin Rasbora is instantly recognizable thanks to its copper-pink body and the triangular black patch that extends from the dorsal fin to the base of the tail — the “harlequin” mark. The contrast between this black wedge and the metallic sheen of its body makes it a standout, especially in planted or dark-substrate tanks.

• Body Shape: Laterally compressed and streamlined

• Sex Differences: Females tend to be slightly larger and rounder; males often have more vibrant coloration

• Color Tip: Their iridescence intensifies under good lighting and with proper diet

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Ideal Aquarium Setup

Harlequin Rasboras thrive in aquariums that replicate their natural Southeast Asian habitat — soft water, low light, and plenty of plants.

Tank Size:

• Minimum: 10 gallons (for a small group)

• Recommended: 20 gallons or more for a full school

Water Parameters:

• Temperature: 72–80°F (22–27°C)

• pH: 6.0–7.5

• Hardness: Soft to moderately hard

• Lighting: Moderate to low

• Substrate: Dark sand or gravel enhances their colors

Decor:

• Live plants (especially taller species)

• Driftwood or branches

• Leaf litter or Indian almond leaves (to mimic blackwater conditions)

? Pro Tip: A black background really makes their copper color shine.

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Behavior and Compatibility

Harlequin Rasboras are schooling fish that should be kept in groups of at least 6–8 individuals — though a group of 10+ will look even more stunning and promote natural, coordinated swimming.

Temperament:

• Peaceful and non-aggressive

• Great dither fish that reduce shyness in other species

Ideal Tankmates:

• Other small, peaceful fish like:

  • Neon tetras

  • Ember tetras

  • Corydoras catfish

  • Otocinclus

  • Dwarf gouramis

  • Cherry barbs (non-aggressive)

  • Shrimp and snails

Avoid larger, aggressive species or fin-nippers like tiger barbs.

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Feeding and Diet

Harlequin Rasboras are omnivores and not fussy eaters, making them easy to care for.

What to Feed:

• Staple: High-quality flakes or micro pellets

• Supplements: Frozen or live daphnia, bloodworms, brine shrimp

• Occasional Treats: Blanched spinach or spirulina-based foods

Feed once or twice a day in small portions that they can finish in 2–3 minutes. A varied diet helps keep their colors rich and supports longevity.

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Breeding Harlequin Rasboras

Breeding in home aquariums is very possible with the right conditions.

Breeding Setup:

• Separate breeding tank (soft, slightly acidic water)

• Temperature around 78–80°F (25–27°C)

• Fine-leaved plants or Java moss for egg laying

Spawning Behavior:

• Males court females with vibrant displays

• Eggs are scattered on the underside of broad leaves

• Remove parents post-spawning to prevent egg predation

• Eggs hatch in 24–36 hours; fry swim free in about 3 days

Feed fry infusoria or commercial fry foods, followed by newly hatched brine shrimp.

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Health and Maintenance

Harlequin Rasboras are hardy and forgiving of minor mistakes, which makes them perfect for beginners. Still, good maintenance ensures a longer and healthier life.