Harlequin Rasbora (Trigonostigma heteromorpha) is a peaceful, vibrant freshwater fish native to Southeast Asia, and it's a favorite among aquarists for its schooling behavior and striking appearance. 

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Species Overview

• Scientific Name: Trigonostigma heteromorpha
• Common Names: Harlequin Rasbora, Red Rasbora
• Family: Cyprinidae
• Size: 1.75–2 inches (4.5–5 cm)
• Lifespan: 5–8 years
• Temperament: Peaceful, shoaling
• Tank Level: Mid-dweller

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Appearance

• Body Color: Copper-orange to pinkish-red
• Markings: Distinctive black triangular wedge on the rear half of the body
• Sex Differences:
  • Males: Slimmer, more vibrant colors, rounded wedge
  • Females: Larger, fuller belly, straighter wedge 

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Tank Requirements

• Minimum Tank Size: 10 gallons (20+ gallons preferred for larger schools)
• Water Temperature: 72–81°F (22–27°C)
• pH: 6.0–7.8
• Hardness: 2–15 dGH
• Substrate: Dark sand or gravel enhances coloration
• Décor: Dense vegetation, floating plants, driftwood, leaf litter
• Lighting: Subdued or dim lighting preferred

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Diet

• Type: Omnivore / Micropredator
• Foods:
  • Flake and micro pellets
  • Live/frozen: Brine shrimp, daphnia, bloodworms
  • Vegetables and algae-based foods
• Feeding Frequency: 2x daily; avoid overfeeding 

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Tank Mates

• Ideal companions:
  • Tetras, Danios, Corydoras, Dwarf Gouramis, Bettas (1 per tank), Shrimp
• Avoid:
  • Large or aggressive fish that may prey on them 

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Breeding

• Method: Egg-layer (not scatterer)
• Spawning Behavior:
  • Female inverts under broad leaves to lay eggs
  • Male fertilizes eggs during spawning dance
• Conditions:
  • pH ~6.0, temp ~80°F (27°C), soft water
  • Use plants like Cryptocoryne or Anubias
• Fry Care:
  • Eggs hatch in ~24–48 hours
  • Fry feed on infusoria, then baby brine shrimp