Max Size: 5cm

Harlequin Rasbora (Trigonostigma heteromorpha)

Harlequin Rasboras are attractive, peaceful, lively and relatively hardy, making them suitable for a well-planted community aquarium with other small temperate fish or in a species only aquascaped nano aquarium.

Harlequin Rasboras are a shoaling fish that you should keep in groups of at least eight individuals. Maintaining these fish in more significant numbers will create a stunning display. You can keep Harlequin Rasboras with most fish, and they will not bother any other species.

Ideal tankmates for the Harlequin Rasboras could include small Tetras, Bettas, Dwarf Barbs, Dwarf Gouramis, smaller Danios, other Micro Rasboras, and Corydoras Catfish. However, You must not house these fish with larger and more aggressive species such as Cichlids and bigger Barbs as they will be seen as an easy snack.

The ideal aquarium setup for your Harlequin Rasboras would be well planted with soft, acidic water, mimicking their natural environment. It would also benefit your fish if you had a soft, dark sandy substrate with driftwood roots and branches placed so that plenty of shady spots and hiding places are formed.

Adding dried leaf litter would also be beneficial and would further accentuate the natural feel as it stains the water brown as they decay. Harlequin Rasboras prefers dim lighting, so adding floating plants to diffuse the light will also be appreciated. However, make sure you give these fish enough room to swim around.

Harlequin Rasboras have reddish copper, metallic affect bodies contrasted by a signature black triangular-shaped wedge that starts at their dorsal fin and continues to the base of their caudal fin. In addition, their fins tend to be lined with red. Captive bred' black' and 'gold' strains of Harlequin Rasboras are also occasionally available.

Quick Facts
Scientific NameTrigonostigma heteromorpha
Year Described1904
Other NamesRed Rasbora, Harlequin Fish, Red Razor
OriginsIndonesia, Malaysia, Singapore, Thailand
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 6+
Lifespan3 - 5 years
Water Parameters
Water TypeFreshwater
PH5.5 - 7.0
GH2 - 15
TDS18 - 215
72 - 80℉
22.2 - 26.7℃


Harlequin Rasbora
Harlequin Rasbora
Longfin Harlequin Rasbora
Harlequin Rasbora
Harlequin Rasboras
Blue Harlequin Rasbora
Harlequin Rasboras
Harlequin Rasboras
Harlequin Rasboras
Harlequin Rasbora
Harlequin Rasbora
Harlequin Rasbora
Harlequin Rasbora

Natural Habitat

Harlequin Rasboras are native to Malaysia, Sumatra, and southern Thailand in Southeast Asia. You can also find these fish in the Nee Soon Swamp in Singapore.

These fish inhabit slow-moving blackwaters in streams, rivers and swamp forests. The water in their habitats is occasionally stained light brown to yellowish due to tannins and other chemicals released by decomposing organic material, and fallen leaves, twigs, and branches usually cover the substrates.

These habitats contain soft, slightly acidic, neutral water and are generally shaded due to the forest canopy above and all the vegetation.


Harlequin Rasboras are omnivores, so they will eat a wide range of foods but make sure it is relatively small as they only have tiny mouths.

These fish will become very active at feeding time and will happily take dried food like flakes or pellets from the surface. However, you will need to supplement the dried foods with small live and frozen foods such as daphnia, brine shrimp and bloodworms.

Sexual Dimorphism

It is pretty easy to determine the sex of a Harlequin Rasbora. The males are slimmer and usually have more distinctive colours than the females, and the triangular patch is rounder and more elongated in the male. In contrast, the females are plumper and typically duller than the males.


Breeding Harlequin Rasboras can be somewhat challenging however it is possible.

You should set up a separate breeding tank with extremely soft, shallow water; peat filtration is recommended. You will also need to add a good amount of broad-leaved plants, which the fish will use to deposit their eggs.

Spawning is often triggered by the first beams of the morning sun, and the females can deposit anything up to 250 eggs underneath the plant leaves. Next, the females will swim beneath a chosen leaf, rub their stomachs against it, ready for spawning, hoping to encourage the mail to join them. When the male joins the female, he repeats the same beside her and then the female releases her eggs and attaches them to the underside of the leaf. Next, the male will curl his tail fin around the female's body and, with a shaking motion, releases the sperm that will fertilise the eggs.

The females will lay six to twelve eggs at a time, and the fish will repeat this process over 2 hours. It is advisable to remove the parents from the breeding tank once all the eggs have been laid; otherwise, the adults may eat the eggs if given a chance. The eggs are light-sensitive, so you must cover the tank's sides to keep the tank in darkness and prevent the eggs from getting fungus.

The eggs will hatch around 24 hours later, and about 72 hours after that, the babies will become free-swimming. The tiny fry will require very small grade foods, starting with infusoria and slowly moving on to more significant foods as they grow. It would be better to perform small frequent partial water changes as the fry are incredibly sensitive to changes.

The Harlequin Rasbora has been featured on the following stamps

Singapore - 1962