Harlequin in Portrait

The harlequin is one of the most popular carp fish due to its pretty color and sociable way of life and is very popular in the community aquarium. The species, which originally came from Southeast Asia, no longer has to be caught in the wild, because it is now reproduced very frequently, especially in breeding farms in Asia and Eastern Europe.


  • Name: Harlequin
  • System: Carp-like
  • Size: about 5 cm
  • Origin: Southeast Asia
  • Attitude: easy to maintain
  • Aquarium size: from 54 liters (60 cm)
  • pH value: 5.0-7.5
  • Water temperature: 22-27 ° C

Interesting facts about the Harlequin

Scientific name

Trigonostigma heteromorpha

Other names

Harlequin barb, Rasbora heteromorpha


  • Class: Actinopterygii (ray fins)
  • Order: Cypriniformes (carp fish-like)
  • Family: Cyprinidae (carp fish)
  • Genus: Trigonostigma
  • Species: Trigonostigma heteromorpha (harlequin harlequin)


The harlequin can reach a total length of 5 cm but usually stay a bit smaller.

Shape and color

This Bärbling is named after a dark wedge spot on the back of the fish, which is also found in a similar form in the other Trigonostigma species (T. espei and T. hengeli) that are occasionally offered in pet shops. Trigonostigma heteromorpha is the most high-backed species of the genus and has red fins.


Harlequin rasbora are widespread in Southeast Asia. Their distribution ranges from Thailand over the Malay Peninsula and Singapore to Sumatra and Borneo. They live mainly in swamp areas with dense vegetation, so they prefer slowly flowing to stagnant water.

Gender differences

The females of the harlequin are usually slightly larger than the males and show a more robust physique. Sexually mature females also develop quite a full belly area. The males are a little more attractively colored.


These danios are not difficult to reproduce under suitable conditions, but for this, you need your own small aquarium, which is best filled with soft and acidic water (pH value around 5-6). You can filter this through a small sponge filter, which only generates a slight movement of water. You should bring in a few large-leaved aquatic plants, and the females will attach their eggs to the underside of these. The very small fry hatch after 1-2 days and initially still carries a yolk sac. After about a week they swim freely and should initially be fed with the finest food (e.g. paramecia).

Life expectancy

With good care, harlequin can easily reach an age of around 6 years and sometimes even get older.

Interesting facts


In nature, the harlequin mainly feeds on small insects and their larvae, crustaceans, and worms. You can also feed them with dry food (flake food, granules, etc.) without any problems. A regular offer of smaller live or frozen food, e.g. B. in the form of water fleas, mosquito larvae, etc. the animals are very happy.

Group size

These danios are very peaceful and sociable fish, which actually only feel at home in a small school and can show their natural behavior. In this respect, you should acquire at least 8-10 animals, but better 20-25.

Aquarium size

An aquarium measuring 60 x 30 x 30 cm (54 liters) is completely sufficient for the care of a small swarm of these danios. If you have a larger school of animals and would like to socialize them with a few other fish, you should perhaps better buy a meter aquarium (100 x 40 x 40 cm).

Pool equipment

These fish feel most comfortable in planted aquariums. However, you should make sure that there is enough free swimming space for a school of fish.

Socialize harlequin harlequin

When caring for harlequin you have many options for possible socialization. Since the fish are very peaceful and adaptable, they can be socialized with virtually all other species that are also not aggressive. Other barbs and danios, loaches, smaller catfish, but also tetra and rainbow fish are particularly suitable as a company.

Required water values

Although these wild animals come from soft waters with an acidic pH value, care for them even in harder tap water is no problem at all. So you don’t necessarily have to make special water for caring for harlequin. The water temperature should be between 22 and 18 ° C.

Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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