The harlequin rasbora is a timeless aquarium classic. Its distinctive copper-orange body marked by a bold black triangular "harlequin" patch from midbody to the tail makes it instantly recognizable. Peaceful, hardy, and a confident schooling fish, it pairs beautifully with virtually every community species and thrives in planted aquariums.
Natural Habitat
Wild harlequins inhabit peat swamp forests and blackwater streams in the Thai-Malay Peninsula, Singapore, and Sumatra. The water is extremely soft and acidic (pH 4.5–6.0), dark with tannins, and warm (73–82°F). They school in large numbers in open water beneath dense forest canopy.
Water Requirements
| Parameter | Ideal Range |
|---|---|
| Temperature | 73–82°F (23–28°C) |
| pH | 6.0–7.5 (captive-bred tolerate neutral) |
| Hardness (GH) | 2–10 dGH |
| Ammonia / Nitrite | 0 ppm |
| Nitrate | <20 ppm |
Tank Setup
A 20-gallon aquarium suits a school of 8–10 harlequins well. They are mid-water swimmers that need open space in the front and center of the tank, with dense planting along the back and sides. Dark substrate and driftwood enhance their copper coloration. They particularly enjoy the gentle flow environment of a mature planted aquarium.
Diet
Omnivores that accept most small foods: quality micro-pellets or flakes as staple, supplemented with frozen daphnia, baby brine shrimp, and cyclops. Feed twice daily in small amounts. Their small mouths require appropriately sized food — standard pellets are often too large.
Temperament & Tank Mates
One of the most peaceful community fish available. Ideal companions: neon tetras, cardinal tetras, corydoras, otocinclus, dwarf gouramis, bettas, and small plecos. Keep in schools of at least 8 — smaller groups lead to shyness and stress. A school of 15–20 harlequins in a planted tank is genuinely spectacular.
Breeding
Harlequin rasboras are egg-adhesion spawners — uniquely, they deposit eggs on the underside of broad leaves (particularly anubias and amazon sword). Condition the pair on frozen foods, then introduce to a soft-water breeding tank (pH 6.0–6.5, GH below 4) with broad-leaved plants. The male embraces the female beneath a leaf while eggs are deposited and fertilized. Remove parents after spawning. Eggs hatch in 24–36 hours; feed fry infusoria then baby brine shrimp.
Content reviewed for rasbora biology accuracy. Breeding behavior verified against published cyprinid spawning literature.