Fish Profiles: Harlequin Rasbora
Fish Profiles: Harlequin Rasbora

One of the most common types of Rasbora you'll find in the shops are Rasbora heteromorpha, the harlequin rasbora, also referred to as the "red rasbora" or simply "the rasbora".

Harlequin rasbora are very popular amongst fish hobbyists, being vibrant in colour and very easy to care for. Harlequin rasbora are an ideal species for smaller-sized community aquarium being a peaceful, shoaling fish.

Here's everything you need to know about the beautiful harlequin rasbora species:

Harelquin rasbora

Origin and Distribution

The harlequin rasbora fish species is a native to Malaysia, Singapore, Sumatra, and southern Thailand. Harlequin rasbora can be found in peat swamps, forest pools and streams with lots of cover and decomposing plant matter - acidic blackwater environments.

Characteristics and Care Parameters

Common names: Red rasbora, the rasbora
Scientific name: Trigonostigma heteromorpha
Adult size: 1.75" / 4.5cm
Life expectancy: 6 years
Family: Cyprinidae 
Origin: Southeast Asia
Temperament: Peaceful, ideal community fish
Ideal number kept together: 8+ for shoaling
Swimming level: top to mid-level
Recommended minimum tank volume: 10 gallon / 45 litres
Diet: Omnivore
Breeding: Egg Layer
Care difficulty: Easy to intermediate
Recommended pH: 6.0 to 7.5
Water hardness: up to 12 dGh
Temperature: 23° to 28° degrees Celsius / 73° to 82° Fahrenheit

harlequin rasbora in tank 


Harlequin rasbora inhabits streams and waters that generally have low mineral content and high concentrations of dissolved humic acids, which is typical of water flowing through swamped forests. These conditions resemble those found in the blackwater habitats of South America.

Rasboras are a freshwater family of fish and are rarely if ever seen in brackish waters. They prefer the lowland waters of southeastern Asia, where the water is soft and acidic. Harlequin rasboras prefer an environment with areas of dense vegetation, an open area for swimming, a dark substrate, and subdued lighting.

An ideal aquarium habitat for housing harlequin rasboras should be planted with live plants, and have plenty of open areas for swimming. Plants of the Cryptocoryne species are among the plants that inhabit the harlequin rasbora's native waters.

Diet and Feeding

Harlequin rasbora will eat most common tropical fish food, and will also eat live foods whenever possible. In nature, their diet is omnivorous, consisting mainly of insects. A varied diet combining flake, granule and frozen food will ensure that digestive problems or susceptibility to disease do not occur. Brine shrimp, daphnia, and any type of worm are excellent supplemental foods, especially when conditioning for breeding.

harlequin rasbora fish 

Colours and Markings

Harlequin rasbora are often referred to as a red rasbora, because the body is a reddish-copper color accented by a striking black wedge covering the rear half of the body. The distinguishing triangular patch begins near the dorsal fin and comes to a point near the base of the caudal fin.

Sexing and Breeding

Male harlequins are more slender and slightly smaller than females. Although they share similar colors and patterns males tend to be more brightly colored than the females. In addition, the distinctive black wedge covering the posterior of the fish may be more rounded in males and more angular in females.

Harlequin rasbora are a difficult tropical freshwater species to breed, but spawning may be achieved under the proper conditions. Younger specimens are recommended for breeding, young harlequins reach sexual maturity within 6-9 months. Most species of rasboras are generally egg-scattering spawners, but harlequin rasboras are egg layers. The best way to prepare them to spawn is to feed a rich live or frozen food diet of bloodworm or dapnia.

It is possible to breed a group of harlequins in a single breeding aquarium or single-species fish tank. When breeding, it is recommended to keep two males for every female. You can go the extra mile and try to simulate natural conditions in the wild, mimicing the concentration of humic acid in the water, but this often isn't necessary.

The basic water chemistry you want to achieve is a pH of between 6.0-6.5, soft water with a hardness of 4 dGh or less, and an optimum water temperature of 24-26° celsius. Broad-leaved plants make an ideal spot to lay eggs, along with large leaf-litter such as broad dried cattappa leaves.

Spawning will usually begin in the morning and starts with the male dancing before the female. This spawning behavior is intended to direct the female to a suitable plant for depositing the eggs. You may see the male prodding the sides and rubbing the back of the female to move her to the egg-laying location.

When ready to spawn, the female turns upside down and rubs her belly against the underside of a leaf, which signals the male to join her. The male will approach her while continuing to dance, and wrap himself around her body fertilizing the eggs as they are released six to twelve eggs at a time.

The fertilized eggs will rise and stick to the underside of the leaf. Spawning typically lasts a couple of hours, during which time as many as 300 eggs may be laid, although 80 to 100 is more likely.

When spawning is complete, remove the breeding stock from the aquarium, otherwise they will eat fry once they hatch. In water temperatures of about 26° degrees Celsius, eggs will hatch in approximately 24 hours. The fry remain attached to the leaf for up to 24 hours, during which time the yolk sac is absorbed. As the fry become free-swimming and grow, feed them copepods or very fine fry food, leading onto brine shrimp after around 14 days.

harlequin rasboras 

Compatible Tankmates

Harlequin rasbora's are an ideal community aquarium fish, but care must be taken not to house them with specimens much larger than them, especially if they can fit in their mouths - they may be mistaken for food. Harlequins do not typically fin-nip, or act aggressivley towards other fish. Common compatible tankmates include cardinal or neon tetra, other rasbora species, small non-aggressive barbs, dwarf gourami, danios (similar species!) and any bottom-feeders like corydoras and plecos. You may also keep them in a shoal with a single Siamese fighter fish.


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Photo credit(s): Canva Pro Licence

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