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Black Harlequin Rasbora
Trigonostigma nigrofasciata
📍 Southeast Asia
The Black Harlequin Rasbora is a striking variant of the classic Harlequin Rasbora, featuring a deep black body with a distinctive dark triangular patch. It is a peaceful, active schooling fish that makes an excellent addition to community aquariums with soft, acidic water. Its bold coloration and lively schooling behavior make it a popular choice among hobbyists seeking a visually dramatic nano or community fish.
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Care Guide
Diet
The Black Harlequin Rasbora is an omnivore that readily accepts high-quality micro pellets and flake foods as a staple diet. Supplement regularly with small live or frozen foods such as daphnia, baby brine shrimp, and micro worms to enhance coloration and conditioning. Feed small amounts two to three times daily, only what the fish can consume within two minutes.
Behavior
Black Harlequin Rasboras are active, peaceful schooling fish that thrive in groups of six or more, displaying their best colors and natural behaviors when kept in larger schools. They occupy the middle water column and are constantly on the move, creating a dynamic and visually appealing display. They are non-aggressive and coexist well with similarly sized peaceful tankmates, making them ideal for community setups.
Breeding
Breeding Black Harlequin Rasboras is moderately challenging and requires soft, acidic water with a pH around 5.5-6.5 and temperatures near 27-28 C (80-82 F). They are egg scatterers that typically deposit adhesive eggs on the undersides of broad-leaved plants such as Cryptocoryne or Anubias. Parents may eat eggs, so removing adults after spawning is recommended; eggs hatch within 24-36 hours.
Tank Mates
Similar size, peaceful, and shares soft acidic water preferences
Peaceful nano fish with matching water parameter requirements
Peaceful bottom dweller that complements the rasbora's middle-zone activity
Gentle, small gourami that shares soft water preferences without aggression
Tiny, peaceful tetra thriving in similar soft acidic conditions
Peaceful algae eater that occupies a different zone and shares water parameters
Common Diseases
Ich (White Spot Disease)
Small white salt-like spots on body and fins, flashing against surfaces, lethargy, and loss of appetite
Raise temperature gradually to 28-30 C (82-86 F), treat with ich medication such as malachite green or copper-based treatments; perform regular water changes
Velvet (Oodinium)
Fine gold or rust-colored dust on skin, rapid gill movement, flashing, clamped fins, and lethargy
Dim tank lighting, treat with copper-based medication or acriflavine; raise temperature slightly and perform water changes
Fin Rot
Fraying, discoloration, or deterioration of fins, sometimes with reddened edges and lethargy
Improve water quality with frequent water changes, treat with antibacterial medication such as kanamycin or erythromycin
Neon Tetra Disease (Microsporidian infection)
Loss of color, white or pale patches on body, curved spine, bloating, and progressive wasting
No reliable cure; isolate affected fish immediately to prevent spread, maintain excellent water quality; euthanize severely affected individuals
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Quick Facts
- diet
- Omnivore – accepts micro pellets, flake food, and small live or frozen foods such as daphnia and brine shrimp
- lifespan
- 3-5 years
- max size
- 4.5 cm (1.75 in)
- tank size
- 10 gallons minimum
- temperament
- peaceful
Water it likes
- ph
- 5.5-7.0
- ammonia
- 0 ppm
- nitrate
- <20 ppm
- hardness
- 1-10 dGH
- temperature
- 72–81°F (22–27°C)