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Harlequin Rasbora
Trigonostigma heteromorpha
Animalia›Chordata›Actinopterygii›Cyprinidae
📍 Thailand, Malaysia & Singapore
The harlequin rasbora is recognised by the distinctive black triangular patch on its rear half set against a copper-orange body. Hardy, peaceful, and active in the midwater, it pairs beautifully with planted tanks.
Care Guide
Diet
Harlequin rasboras are omnivores that thrive on a varied diet of high-quality flake food, micro pellets, and small frozen foods like daphnia and brine shrimp. Feed small portions once daily, offering only what they can consume in 2-3 minutes. Occasional live foods enhance coloration and support natural foraging behavior.
Behavior
These active, peaceful schooling fish are most comfortable in groups of 8 or more, where they display natural shoaling behavior and reduced stress. They occupy the midwater column, constantly moving and exploring, making them ideal for planted aquariums. They are non-aggressive toward other peaceful species and rarely nip or harass tank mates.
Breeding
Breeding harlequin rasboras in captivity is moderately difficult and requires specific conditions including soft, acidic water (pH 5.0-6.0), dense vegetation for egg scattering, and temperatures around 26-28°C. Successful spawning produces 200-300 eggs, but fry survival rates are low without careful management of water quality and live food availability. Most hobbyists find breeding challenging without dedicated breeding tanks.
Tank Mates
Peaceful bottom-dweller with identical water parameter requirements; excellent algae control without competing for food
Similar size, temperament, and water preferences; creates beautiful mixed schooling displays
Peaceful schooler with matching water chemistry needs and compatible midwater behavior
Peaceful and non-aggressive; slightly different water layer preference adds diversity without conflict
Peaceful invertebrates that occupy different ecological niche; may occasionally be eaten by larger rasboras but generally compatible
Common Diseases
Ich (Ichthyophthirius multifiliis)
White spots on body and fins, rapid breathing, lethargy, rubbing against objects
Raise temperature to 28-30°C, perform 25% water changes daily, use aquarium salt (1 teaspoon per 5 gallons) or commercial ich treatment; maintain for 7-10 days
Fin Rot
Frayed or disintegrating fins, white or black edges on fins, lethargy
Improve water quality with frequent partial water changes, reduce stocking density, use antibacterial medication if severe; ensure ammonia and nitrite remain at 0 ppm
Bacterial Infection
Redness on body or fins, open sores, cloudy eyes, loss of appetite
Perform 50% water change immediately, maintain pristine water conditions, use broad-spectrum antibiotic medication; isolate severely affected fish if possible
Velvet Disease (Oodinium)
Fine golden or rust-colored dust on body, rapid breathing, clamped fins, scratching behavior
Raise temperature to 28-30°C, reduce light exposure, use copper-free velvet treatment; perform daily 25% water changes and treat for 7-10 days
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Quick Facts
- diet
- Omnivore – flake, micro pellets, daphnia, brine shrimp
- lifespan
- 5–8 years
- max size
- 4.5 cm (1.8 in)
- tank size
- 10 gallons minimum
- school size
- 8+
- temperament
- Peaceful, schooling
Water it likes
- ph
- 6.0–7.5
- ammonia
- 0 ppm
- nitrate
- <20 ppm
- hardness
- 1–12 dGH
- temperature
- 72–81°F (22–27°C)