Rasbora Harlequin (Trigonostigma Heteromorpha)

The Harlequin Rasbora is one of the most iconic and enduringly popular fish in the aquarium hobby. For over a century, it has been the "gold standard" for community tanks due to its hardiness, peaceful nature, and striking geometric patterns.

As a web developer and Shopify expert, Iwan, you’ll recognize this fish as a "Best Seller." Its distinctive "black lambchop" shape makes it instantly recognizable in thumbnails, making it a perfect anchor product for any "Beginner-Friendly" or "Community Schooling Fish" collection on your site.

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Harlequin Rasbora (Trigonostigma heteromorpha)

The Harlequin Rasbora is a masterpiece of natural design. Native to the blackwater streams of Southeast Asia (including your home region of Indonesia), it features a shimmering copper-pink body and a bold, black triangular patch on the rear half of its body. When kept in a healthy, well-planted environment, their colors deepen into a rich, glowing orange. They are famous for their tight schooling behavior and their playful, active presence in the middle and upper layers of the tank.

Key Information

• Common Name: Harlequin Rasbora, Red Rasbora

• Scientific Name: Trigonostigma heteromorpha

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

• Max Size: 4–5 cm

• Lifespan: 5–8 years

• Temperament: Very peaceful (Ideal community resident)

• Diet: Omnivore – Readily accepts flakes, micro-pellets, and frozen foods like daphnia or bloodworms.

• Care Level: Easy (Very hardy)

Water Parameters

Parameter	Value
Temperature:	23–28°C
pH:	6.0–7.5 (Prefers slightly acidic)
Hardness:	2–12 dGH
Minimum Tank Size:	60L+ (Needs horizontal swimming space)

Behaviour & Tank Compatibility

Harlequin Rasboras must be kept in a group of at least 8–10. In a large group, they feel secure and will engage in beautiful schooling displays. They are among the most peaceful fish available and are compatible with almost any non-aggressive species. Ideal tank mates include Neon Blue Acaras, Celestial Pearl Danios, Gouramis, Corydoras, and Neocaridina Shrimp.

Ideal Tank Setup

• Dense Planting: They look best against a lush green backdrop of Amazon Swords, Cryptocorynes, and Java Fern.

• Dark Substrate: Using dark sand or soil will make their copper-orange body and black triangle stand out much more vividly.

• Moderate Water Flow: They enjoy a gentle current that mimics their native slow-moving jungle streams.

• Open Swimming Area: While they like plants for security, ensure the center of the tank is clear so they can school freely.

• Tannins: They thrive in "blackwater" conditions. Adding driftwood or catappa leaves will lower the pH and enhance their colors.