Harlequin rasbora
Trigonostigma heteromorpha
easy careOverview
The harlequin rasbora (Trigonostigma heteromorpha) is a small, hardy shoaling fish from Southeast Asia and a long-standing favourite in the hobby. Its warm copper body and bold black “pork-chop” triangle make a tight shoal look striking against green plants. Peaceful, adaptable and long-lived, it is one of the easiest community fish to recommend to a beginner running a properly cycled tank.
Tank & water
Give a shoal of six a minimum of 40 litres (10 gallons), with 60 litres or more preferred for a larger group. Harlequins are mid-water swimmers that need open swimming lanes plus planted cover.
- Temperature: hold 22–27 °C with a reliable heater; they are tropical and do best kept stable.
- Filtration: a gentle filter keeps water clean without a fierce current.
- Water: soft to moderately hard, pH 6.0–7.5. They tolerate a range, but stable, dechlorinated water matters more than chasing exact numbers.
- Planted: dark substrate and plenty of plants deepen their colour and make them feel safe.
Feeding
Harlequins are easy-going omnivores. Feed a good-quality micro-pellet or flake food as the staple, sized for small mouths, with regular treats of frozen or live daphnia, cyclops, baby brine shrimp and bloodworm. Feed small amounts once or twice a day — only what the shoal clears in a couple of minutes — to keep water quality high.
Tankmates
Peaceful and non-nippy, harlequins suit almost any calm community. Excellent companions include other small rasboras such as the lambchop rasbora, celestial pearl danios, small tetras, corydoras, pygmy loaches, dwarf gouramis and shrimp. Avoid large or aggressive fish that see them as food.
Set them up in a mature, planted tank with a full shoal and harlequin rasboras are a rewarding, trouble-free centrepiece. Browse our nano aquarium picks and beginner tanks to get started.
Harlequin rasbora — frequently asked questions
How many harlequin rasboras should I keep together?
At least six, and ideally eight to ten or more. Harlequins are a shoaling species that feel secure and colour up best in numbers. Kept in ones and twos they hide, fade and behave nervously, so buy a group from the start.
What size tank do harlequin rasboras need?
A shoal of six is comfortable in a 40-litre (10-gallon) tank, though a 60-litre or larger tank lets you keep a bigger, more impressive group and stays more stable. They are active mid-water swimmers, so length matters more than height.
Are harlequin rasboras good for beginners?
Yes. They are hardy, adaptable to a range of water parameters, peaceful and inexpensive, which makes them one of the best beginner shoaling fish for a cycled community tank.
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