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 (GH): 18–215 ppm (1–12 dGH)
Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.
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 Smaller groups become withdrawn and pale.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
- Glass Catfish
- Lambchop Rasbora
- Pristella Tetra
- Dwarf Neon Rainbowfish
- Three-Line Corydoras
- Scissortail Rasbora
- Lemon Tetra
- Diamond Tetra
- Black Phantom Tetra
- Penguin Tetra
Avoid keeping with
- Betta
- 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: 2026-06-18