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Harlequin Rasbora

By The Aquarium Calculators Editorial Team ·

Trigonostigma heteromorpha

Complete Harlequin Rasbora care guide covering omnivore diet requirements, peaceful temperament, minimum 10 Gallons tank setup, and compatible freshwater tankmates. Difficulty: Easy.

Harlequin Rasbora

Quick Answer

Harlequin Rasbora (Trigonostigma heteromorpha) is a captivating and highly sought-after freshwater species. It requires a minimum 10 Gallons aquarium with a pH of 6.5 - 7.5 and temperature range of 22-26°C. This omnivore occupies the middle zone and makes an excellent addition to community setups.

Intro

Harlequin Rasbora (Trigonostigma heteromorpha) is a captivating and highly sought-after freshwater species. Known for their peaceful nature and distinct appearance, they occupy the middle levels of the aquarium and bring dynamic energy to any setup.

Setup

Harlequin Rasbora requires a stable, well-filtered aquarium of at least 10 gallons. They thrive best with moderate water movement and a reliable heater to maintain temperatures around 22-26°C. Ensure pH levels remain consistent between 6.5 - 7.5 to prevent stress and support long-term health.

Feeding

As a omnivore, the Harlequin Rasbora is not a picky eater. They should be fed a high-quality base of flakes, sinking pellets, or wafers. Periodic supplementation with frozen or live foods, such as bloodworms or brine shrimp, will boost their health and colors.

Compatibility

Harlequin Rasbora has a peaceful temperament. They are schooling fish and MUST be kept in a group of at least 6 individuals to exhibit natural schooling behavior and reduce stress. Avoid placing them with aggressive species or tankmates they are listed as incompatible with, such as: None.

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Tank Position
Middle
Water Temp
22-26°C
Adult Size
See profile
Water pH
6.5 - 7.5

Species Characteristics

Adult Size
Lifespan
Growth Rate
moderate
Tank Compatibility
Community compatible
Indoor Aquarium
Yes

Water Parameters

Water Temperature
Humidity
Water pH

Tank Lighting

Tank Lighting
Standard lighting
Light Hours
N/A
Intensity
moderate

Feeding & Diet

Diet Type
Diet: Omnivore
Feeding Schedule
N/A
Live Food Options
N/A

Continue Learning

Recommended Tools

Fish Compatibility Calculator fish compatibility

Health & Disease

Ich (White Spot Disease) common disease • all fish

Related Guides

Understanding pH in Aquariums water parameters • ph

Similar Species

African Red Eyed Tetra Care Guide: Schooling & Tank Size semanticSimilarity Apistogramma Care Guide: Temperament & Diet semanticSimilarity Banded Corydoras Care Guide: Substrate & Diet semanticSimilarity

Frequently Asked Questions

How many Harlequin Rasboras should be kept together?
Maintain a minimum school of 8 to 12 individuals in a tank of at least 15 gallons (57 liters) with a footprint of 24x12 inches (60x30 cm). Harlequin rasboras (Trigonostigma heteromorpha) are schooling fish that display their signature black wedge only in groups over 8. Groups under 6 cause faded colors, fin-nipping, and chronic hiding. A school of 15+ creates natural shoaling dynamics. Provide dense planting (Cryptocoryne, Java fern) and dark substrate. Tank length must exceed 24 inches (60 cm) for their active midwater swimming.
What are the exact water parameters for Harlequin Rasboras?
Target pH 6.5 - 7.5, General Hardness 3 - 10 dGH, Carbonate Hardness 2 - 8 dKH, Total Dissolved Solids 80 - 250 ppm, Electrical Conductivity 160 - 500 μS/cm, and temperature 72°F - 80°F (22°C - 27°C). They prefer stable parameters; sudden shifts cause stress. Maintain nitrates below 15 ppm with weekly 20% water changes. Use a sponge or HOB filter with moderate flow. Add driftwood and floating plants to diffuse light. Hardness below 3 dGH causes clamped fins.
What is the dietary and medication protocol for Harlequin Rasboras?
They are omnivores requiring 35% protein, 10% fat, 55% plant matter. Feed premium flake food, small pellets, frozen daphnia, brine shrimp, and bloodworms twice daily. Offer spirulina flakes weekly. Medication alert: Tolerate copper (0.2 mg/L) but sensitive to formalin. Praziquantel is safe. Salt baths up to 5 ppt treat external parasites. Quarantine with methylene blue for 7 days. They are susceptible to ich; treat with malachite green at half-dose (0.05 mg/L).
How to breed Harlequin Rasboras in a home aquarium?
Select 10-12 mature fish and condition with live blackworms and brine shrimp for 2 weeks. Set up a 10-gallon (38 liter) breeding tank with 5 inches (12 cm) of water (pH 6.5, dGH 5, 78°F/25.5°C), a spawning mop, and fine-leaf plants (Cryptocoryne). Simulate dawn with gradual light. Spawning occurs in the morning; female releases 100-200 adhesive eggs on underside of leaves. Remove parents after 4 hours. Eggs hatch in 24-30 hours at 75°F (24°C). Fry feed on infusoria for 3 days, then microworms, then baby brine shrimp after day 7.

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