Harlequin Rasbora (Trigonostigma heteromorpha) Fish Species Profile

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The Harlequin rasbora is a small, peaceful and playful fish.

The species became a favourite among hobbyists after its introduction in the early 1900s.

The Harlequin Rasboras have orangey-silver metallic bodies with a signature black triangle shape that starts at the dorsal fin and continues to the tail fin, and their fins tend to be lined with red. This fish is relatively hardy and can live aside pretty much any tankmates that aren't aggressive, or they become timid and tend to hideaway.

Scientific NameTrigonostigma heteromorpha
Other NamesRed Rasbora, Harlequin Fish, Red Razor
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 6+
Lifespan3 - 5 years
Maximum Sizeup tp 5 cm
Water Conditions
Water TypeFreshwater
Temperature72 - 80 ℉ (22.2 - 26.7 ℃)
PH5.5 - 7
GH2 - 15

Origins of the Harlequin Rasbora

The Harlequin rasbora is native to Malaysia, Singapore Sumatra and southern Thailand. It lives in streams, rivers, and swamp forests, and other watercourses with soft, slow-moving, calm, low acidic and neutral water, low mineral content, and high concentrations of dissolved humic acids.

They prefer high vegetation in their habitat, which provides the much-needed shade that they need.


Harlequin Rasbora is an omnivore, so will eat a wide range of foods but make sure it is relatively small as they only have little mouths.

At feeding time, these fish will become very active and will happily take flakes or pellets from the surface, but you will also need to feed them live or frozen foods such as Daphnia and Bloodworms.

Sexing the Harlequin Rasbora

It is easy to determine the sex of a Harlequin Rasbora.

The male harlequin rasboras usually have more distinctive colours than the females, and the triangular patch is rounder and more elongated in the male. The females are plumper than the males.

Breeding the Harlequin Rasbora

For successful breeding, the water must be soft and acidic, as the fish are unlikely to spawn in hard, alkaline water.

The Harlequin rasbora deposits sticky eggs underneath leaves of plants. The female will swim beneath a chosen leaf, rub her stomach against it ready for spawning hoping to encourage the mail to join her.

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. The male will curl his tail fin around the body of the female and with a shaking motion, releases the sperm that will fertilise the eggs. She will lay six to twelve eggs at a time, and the fish will repeat this process over 2 hours or so and once completed, she may lay up to 300 eggs.

It is advisable to remove the parents from the aquarium once eggs have been laid as they may eat the eggs.

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Date Added: 6/2/2020 - Updated: 6/5/2020 11:31:44 AM