6 × Harlequin Rasboras (Trigonostigma heteromorpha)

This listing is for a group of 6 Harlequin Rasboras (Trigonostigma heteromorpha). Older aquarium books and product labels may still use the former name Rasbora heteromorpha, but Trigonostigma heteromorpha is the accepted name used on this listing.

Harlequin Rasboras are peaceful, active shoaling fish recognised by their copper-orange body and dark wedge-shaped flank marking. They are excellent display fish for a mature planted community aquarium because the group creates steady midwater movement without the territorial behaviour associated with many larger species.

The pack contains six fish, but six is not our recommended final social group. We recommend keeping at least eight Harlequin Rasboras where aquarium capacity allows. Treat this six-fish product as a starter pack or an addition to an existing compatible shoal.

What you are buying

• Sale unit: 6 Harlequin Rasboras
• Scientific name: Trigonostigma heteromorpha
• Former/common scientific combination: Rasbora heteromorpha
• Supplied size: approximately 2.5–3 cm
• Maximum recorded size: FishBase records up to 5.0 cm total length
• Recommended group: 8+ fish where aquarium capacity allows
• Aquarium guidance: about 60 litres and at least 60 cm of useful swimming length
• Routine temperature guidance: 22–25°C
• pH guidance: about 5.0–7.0
• Hardness guidance: about 5–12 dGH
• Temperament: peaceful
• Diet: omnivore

Appearance and natural behaviour

The classic black wedge is the feature that makes a true Harlequin Rasbora so easy to recognise. In settled fish the copper-orange body contrasts strongly with the dark flank marking, especially in a planted aquarium with shaded areas and a darker background.

These are not solitary display fish. Their strongest visual effect comes from keeping a proper group and giving that group enough horizontal space to move together. A cramped aquarium or token group can reduce the very behaviour that makes Harlequins attractive.

Aquarium setup

Use a fully cycled, mature aquarium with stable filtration. We recommend at least 60 cm of swimming length and around 60 litres for one proper group, before considering other livestock. Tank dimensions, adult tank mates, planting and filtration all matter, so the litre figure should not be used as an automatic stocking permission.

Planting around the back and sides works well because it gives the shoal cover while preserving open midwater. Floating plants or taller stems can soften bright lighting. Gentle to moderate circulation is suitable; the aim is clean, oxygenated water without forcing the fish to swim constantly against strong current.

Do not choose a tall narrow tank simply because its volume looks sufficient. Harlequin Rasboras use horizontal swimming room, and the usable length after hardscape matters more than a headline litre figure on its own.

Water parameters

For Harlequin Rasboras, use 22–25°C, pH 5–7 and 5–12 dGH as the starting range. These are practical aquarium values, not a promise that every fish will fail outside one exact number.

Test the source water and the aquarium water before purchase. Stable conditions are more important than aggressively altering chemistry to chase a target. If the fish are moving from different holding water, gradual acclimation and careful observation are more useful than a fixed one-size-fits-all recipe.

Feeding

Use a complete small tropical fish food as the staple: fine flakes, micro-pellets or small granules that the fish can take easily from midwater. Add suitable frozen or live foods such as daphnia, cyclops or small brine shrimp for variety.

Feed in a way that lets the entire shoal participate. In busy community tanks, very fast feeders can take everything before Harlequins settle into the meal. Small controlled portions help maintain body condition without allowing excess food to break down in the aquarium.

Tank mates

Harlequin Rasboras suit peaceful community fish that share compatible water and are not large enough to treat them as prey. Calm Corydoras, suitable small loaches, peaceful gouramis and many similarly sized community fish can work when the full aquarium is planned around adult size and water needs.

Avoid large predators, highly territorial cichlids and persistent fin nippers. Also avoid using a generic “community fish” label as proof of compatibility; temperature, water chemistry, adult size and feeding behaviour still have to overlap.

Why this six-fish pack is a starter or add-on pack

The product quantity is a commercial unit, not a welfare target. Six fish can be useful if you already keep Harlequins and want to increase the group, or if you are intentionally buying more than one pack for a suitable aquarium. Our long-term recommendation is at least eight fish, with additional space required as the group and community grow.

Before ordering

Choose this pack if the aquarium is mature, at least around 60 cm long, and you have a clear plan for an appropriate long-term shoal. Reconsider if the tank is newly filled, very small, already crowded, or if the six fish would have to remain as the final group indefinitely.

For more on Trigonostigma heteromorpha taxonomy, distribution, maximum size, group guidance, water guidance and breeding behaviour, use our Harlequin Rasbora Care Guide. This product page focuses on the six-fish sale unit and the buying decision, while the care guide carries the full scientific references.