Harlequin rasbora - Trigonostigma heteromorpha

Scientific name: Trigonostigma heteromorpha

Common name: Harlequin rasbora

Family: Cyprinidae

Usual size in fish tanks: 3 - 5 cm (1.18 - 1.97 inch)

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Recommended pH range for the species: 5 - 7

Recommended water hardness (dGH): 4 - 12°N (71.43 - 214.29ppm)

0°C 32°F30°C 86°F

Recommended temperature: 23 - 28 °C (73.4 - 82.4°F)

The way how these fish reproduce: Spawning

Where the species comes from: South Asia

Temperament to its own species: peaceful

Temperament toward other fish species: peaceful

Usual place in the tank: Top levels

Tank Requirements

Harlequin Rasboras (Trigonostigma heteromorpha) thrive in a well-planted aquarium with ample swimming space at the top levels. As schooling fish, they need to be kept in groups of at least 6 to 8 individuals, which helps them feel secure and exhibit their natural behaviors. A minimum tank size of 40 liters (10 gallons) is recommended to provide enough space for a small school.

These fish prefer soft, slightly acidic water, with a pH range of 5.0-7.0 and water hardness between 4-12°N (71.43-214.29 ppm). The ideal temperature range is 23-28°C (73.4-82.4°F). To mimic their natural habitat, include plants such as Cryptocoryne and Amazon Swords, along with some floating plants to provide shaded areas. A dark substrate will enhance their colors, and a gentle filtration system will maintain calm water conditions, which they prefer.

Tankmates

Harlequin Rasboras are peaceful and do well in community aquariums with other similarly non-aggressive fish. Ideal tankmates include:

They are best kept with other peaceful species that thrive in similar water conditions, avoiding larger, more aggressive fish that may stress them or see them as food.

Food and Feeding

Harlequin Rasboras are omnivorous and will accept a variety of foods. A high-quality flake or micro-pellet food can be used as their staple diet. To provide balanced nutrition, offer live or frozen foods such as daphnia, bloodworms, and brine shrimp, which help bring out their vibrant colors. They also enjoy small, crushed vegetable-based foods. Feeding them twice a day in small amounts ensures they get enough nutrition without polluting the water. Make sure all food particles are small enough to fit into their mouths, as they have relatively small mouths.

Sexing

Sexing Harlequin Rasboras can be subtle. Males are typically slimmer and have a brighter coloration, especially during breeding periods. Females are slightly rounder, particularly when carrying eggs, and may have a more subdued hue compared to the males.

Breeding

Harlequin Rasboras are relatively easy to breed in captivity. Set up a separate breeding tank with plenty of fine-leaved plants such as Java Moss or spawning mops. The water should be soft and slightly acidic, with a pH around 6.0 and a temperature of 26°C (78.8°F) to encourage spawning.

The female will scatter up to 100 eggs among the plants, which will hatch in approximately 24 hours. It is crucial to remove the parents after spawning, as they may eat the eggs. The fry can initially be fed powdered fry foods or infusoria until they are large enough to accept crushed flakes or baby brine shrimp. Maintaining pristine water conditions in the fry tank is essential for their survival and growth.

Lifespan

With proper care and a well-maintained environment, Harlequin Rasboras can live up to 6 years in captivity, making them a rewarding addition to a peaceful community tank.

Origin

Harlequin Rasboras are native to Southeast Asia, primarily found in slow-moving waters in Thailand, Malaysia, and Indonesia. They inhabit forest streams and swamps with dense vegetation, where the water is soft, slightly acidic, and often shaded by overhanging foliage.

Short Description

Trigonostigma heteromorpha, commonly known as the Harlequin Rasbora, is a popular schooling fish that adds a dynamic splash of color to community aquariums. With its distinctive black triangular patch on the body and peaceful nature, it makes an excellent choice for aquarists of all levels. To truly appreciate their natural behavior and vibrant appearance, keep them in groups of six or more, in a well-planted tank with soft, acidic water conditions.