Maximum size : 5 cm

Harlequin Rasbora - Trigonostigma heteromorpha : Complete Fish Profile & Care Guide

Table of contents


Harlequin Rasboras (Trigonostigma heteromorpha) are a wonderful addition to any aquarist's collection, with their striking appearance and lively behaviour. These peaceful and hardy fish are perfect for a community aquarium or a nano aquascape. Keeping Harlequin Rasboras in groups of eight or more will create a stunning display and allow you to observe their natural shoaling behaviour. 

These fish are compatible with most small temperate fish, such as Tetras, Bettas, Dwarf Barbs, and Gouramis, but should not be housed with larger or more aggressive species. For the ideal aquarium setup, mimic their natural environment with soft, acidic water and plenty of plants, driftwood, and leaf litter. Providing dim lighting and floating plants will create a natural feel and add to their comfort.

Harlequin Rasboras have a copper-red metallic body with a signature black triangular wedge and red-lined fins. Captive-bred black and gold strains are also available, adding to the variety of this already captivating fish. Feeding Harlequin Rasboras is relatively easy; they are omnivores and will readily accept dried foods like flakes and pellets, supplemented with small live and frozen foods such as daphnia, brine shrimp, and bloodworms. Overall, Harlequin Rasboras are a beautiful, peaceful, and fascinating addition to any aquarium, providing a lively display and adding a touch of elegance to any aquascape.

Harlequin Rasbora Photos

Sexual Dimorphism

The process of identifying the gender of Harlequin Rasboras is relatively straightforward. Males tend to have more striking colours and a slimmer physique than their female counterparts. In addition, the triangular patch on the male's body is typically rounder and more elongated than in females. On the other hand, females tend to have a plumper body shape and less distinct colouration compared to males.

Featured Male
Featured Female
Female Male

Quick Facts

Scientific NameTrigonostigma heteromorpha
Year Described1904
Other NamesRed Rasbora, Harlequin Fish, Red Razor
OriginsThailand , Malaysia , Singapore , Indonesia
Max Size5 cm
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 6+
Diet & FeedingOmnivore
ReproductionEgg Depositor
LifespanUp to 8 Years

Water Parameters

Water TypeFreshwater
pH 6 - 7
GH 2 - 15
TDS 18 - 215
Ideal Temperature
72 - 82
22 - 28

The Harlequin Rasbora has been featured on the following stamps.

Natural Habitat

Harlequin Rasboras are native to Malaysia, Sumatra, and southern Thailand, located in Southeast Asia. In addition to these areas, you can also find Harlequin Rasboras in the Nee Soon Swamp in Singapore, where they inhabit slow-moving blackwaters in streams, rivers, and swamp forests. Harlequin Rasboras typically occupy habitats with water that is slightly acidic, neutral, and soft.

These environments are usually shaded, owing to the forest canopy above and the dense vegetation surrounding them. Fallen leaves, twigs, and branches often cover the substrates, creating a perfect environment for the fish to feed, shelter, rest, and hide. Adding Harlequin Rasboras to your aquarium is an excellent way to showcase their unique beauty and contribute to their conservation efforts.


Breeding Harlequin Rasboras can be a challenging yet rewarding experience for aquarists. To successfully breed these fish, it is recommended to set up a separate breeding tank with soft, shallow water and peat filtration. Broad-leaved plants should also be added to provide a suitable spawning site. Spawning usually occurs in the morning, triggered by the first rays of sunlight. Females can lay up to 250 eggs on the underside of leaves, with males fertilizing them using a shaking motion.

The process may last up to two hours, with the female laying six to twelve eggs at a time. After the eggs are laid, it is crucial to remove the parents from the breeding tank to prevent them from eating the eggs. The tank should be covered to prevent light exposure and fungus growth. Hatching occurs around 24 hours after laying, and the fry will become free-swimming 72 hours later.

These tiny fry require small-grade foods, starting with infusoria and gradually moving on to more significant foods as they grow. Frequent partial water changes are necessary as the fry is highly sensitive to changes. Overall, breeding Harlequin Rasboras requires careful attention to water quality and the right environment for the fish to spawn.

Diet & feeding

Harlequin Rasboras have an omnivorous diet and will accept a variety of food sources; however, their small mouths require relatively small-sized foods. During feeding time, Harlequin Rasboras become very active and will eagerly consume high-quality dried foods like flakes or pellets. To ensure a balanced diet, it is recommended to supplement their diet with small live and frozen foods such as daphnia, brine shrimp, and bloodworms.

Frequently asked questions

Harlequin Rasboras thrive in slightly acidic, soft water environments, similar to their natural habitat in the peat swamps of Southeast Asia. They prefer a temperature range of 72-82°F (22-28°C) with a pH between 6.0 and 7.0. Providing a well-planted tank with a dark substrate can mimic their natural habitat and make them feel comfortable.

Provide a well-filtered aquarium with stable water conditions. They appreciate some water movement, as well as a variety of plant life to hide in. Regular feeding with a balanced diet and maintenance to keep the water clean and free from toxins is essential.

With proper care and optimal living conditions, Harlequin Rasboras typically live between 5 to 8 years in captivity.

They are omnivores and accept a wide range of food, including high-quality flake food, freeze-dried and live foods like daphnia, brine shrimp, and bloodworms. A varied diet will help keep them healthy and vibrant.

Males are generally slimmer and more brightly colored than females. Females tend to be larger, rounder, and slightly less colorful. The black patch on the side of the body is straight in females and curved in males.

Harlequin Rasboras are small, colorful fish, typically reaching about 2 inches in length. They are known for their distinct triangular black patch starting from the dorsal fin and extending to the caudal fin. The body color is usually a metallic pink or orange.

Condition the fish with high-quality foods and simulate a drop in water temperature, mimicking the onset of the rainy season in their natural habitat. Provide a breeding tank with fine-leaved plants on which the female can lay her eggs. After spawning, remove the parents to prevent them from eating the eggs.

Yes, they are peaceful fish and do well in community tanks. They can be paired with other small, non-aggressive fish like Tetras, Guppies, and other Rasboras. Avoid housing them with larger, aggressive fish that might see them as food.

Like many fish, Harlequin Rasboras can be susceptible to ich, a parasitic disease that manifests as white spots on the fish. Maintaining good water quality can help prevent this. If it does occur, various over-the-counter treatments are available.

Harlequin Rasboras can reach up to 2 inches (5 cm) in length. As schooling fish, they should be kept in groups of at least 5-6. For such a group, a tank of at least 20 gallons is recommended to provide them with adequate swimming space.

Other Rasboras of interest