Trigonostigma heteromorpha: living card for the harlequin rasbora

Trigonostigma heteromorpha (harlequin rasbora) is a calm community fish, but its behaviour improves when the group is real rather than symbolic.

Quick read

• Type: small schooling cyprinid.
• Aquarium: mature planted tank with front swimming space.
• Indicative temperature: 23-27 C.
• pH: 6.0-7.5.
• Hardness: soft to moderate.
• Base volume: 70 L for 10 or more fish.
• Feeding: micro pellets, fine flakes, and small frozen foods.
• Difficulty: low-medium; benefits from stability and group size.

What to check before buying

Look for a cohesive group, clear triangular patch, and full bodies. Avoid isolated, pale fish or twitchy swimming.

Before buying, confirm that the aquarium is cycled, the group size or pair plan makes sense, and the setup runs at the species’ real temperature.

Aquarium design

Side planting, a somewhat dark background, and gentle current allow visible swimming without exposing the group. Do not fill the whole front with decor.

Use the card as a baseline, then watch the fish. Loss of colour, constant hiding, or all-day competition calls for a design correction before a chemical fix.

Working parameters

It is adaptable if transitions are slow. Filter stability and regular changes matter more than chasing perfect blackwater.

Treat these ranges as a working zone, not permission to swing parameters. Rapid changes, immature aquariums, and incompatible species cause most problems.

Compatibility and warning

It works with calm tetras, corydoras, and peaceful labyrinth fish. Avoid overly fast competitors or large predators.

If the group hides permanently, check light, cover, group size, and intimidating tankmates.

Reference sources

FishBase for taxonomy and distribution; NOAA/University of Florida historical ornamental-trade data for frequent market species; Aquarium Co-Op and specialist aquarium guides for practical husbandry ranges.