Harlequin Rasbora

Trigonostigma heteromorpha

Also known as: Harlequin fish, Red rasbora

Quick Facts

• Adult size: 3.5-4.5 cm (1.75-1.8 inches)
• Minimum tank size: 55 litres (14.5 gallons)
• Lifespan: 5–8 years
• Temperament: peaceful
• Swimming level: middle
• Diet: omnivore
• Minimum group size: 8
• Difficulty: beginner

Water Parameters

• Temperature: 21–28°C
• pH: 5–7.5
• Hardness: 18–215 ppm

Care Summary

A long-standing community-tank favourite, known for its distinctive black triangular patch on a copper-pink body. Hardier and longer-lived than its similar-sized cousin the neon tetra, with no equivalent of neon tetra disease. Schools tightly in the middle of the water column, particularly in groups of 10+. Performs best in densely planted tanks with subdued lighting; bright open tanks can leave them washed out. A reliable, undemanding fish that's often the better choice over neons for hard-water Australian tap supplies if you're willing to soften the water slightly.

Tankmates

Peaceful schooling species that must be kept in groups of at least 8 — ideally 10 or more — to display natural shoaling behaviour and full colour. Smaller groups become withdrawn and pale. Excellent tankmate for most peaceful community species of similar size. Naturally soft, slightly acidic blackwater habitat; tolerates harder water but shows best colour in soft, tannin-stained tanks.

Compatible with

• Neon Tetra
• Bronze Corydoras
• Ember Tetra
• Cherry Shrimp
• Otocinclus
• Mystery Snail
• Kuhli Loach

Avoid keeping with

• Betta
• Angelfish Adult
• Fin Nippers
• Large Cichlids

Common Problems

• loss of colour in small groups or bright tanks
• ich
• sensitivity to sudden parameter changes
• fin nipping if kept with aggressive tankmates

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-02