Beautiful Aquarium Fish: Harlequin Rasbora

The harlequin rasbora (Trigonostigma heteromorpha), is a very fashionable and nice-looking cyprinid aquarium fish.  It is hardy fish with brilliant body coloration. In 1904, it was first described by Duncker and it has placed in Cyprinidae family (Minnows or carps)) under Order Cypriniformes of Class Actinopterygii (=Ostecihthyes). It is now listed as Least Concern (LC) on the IUCN Red Data List. Urbanization, drainage, overfishing for the aquarium trade is the main threats for this fish. Synonym of this species is Rasbora heteromorpha Duncker, 1904.

Systematic Position

  • Phylum: Chordata
  • Subphylum: Vertebrata
  • Class: Actinopterygii (=Osteichthyes)
  • Order: Cypriniformes
  • Family: Cyprinidae
  • Subfamily: Danioninae
  • Genus: Trigonostigma
  • Species: Trigonostigma heteromorpha (Duncker, 1904)

Distribution and Habitat

It is distributed in Singapore, southern Thailand, Sumatra, and Malaysia. In nature, it prefers to live in the calm or gently flowing waters of streams, rivers, ditches, canals where peat swamp forests with heavily vegetated waters are available.

Common Names

It has several common names due to color variations such as Harlequin Fish, Harlequin, Red Rasbora, Black Harlequin Rasbora, Gold Harlequin Rasbora and Blue Harlequin Rasbora.

Body Shape

Body is an elongated and laterally compressed with small, terminal mouth and deeply forked caudal fin. The dorsal fin is large and upright while anal fin has 5 branched rays. The mouth does not contain any Barbel and lateral line is incomplete with 6-9 pores.

Body Colors

Topside and bottom of the body is pale pink or bright red to a copper orange in colors while the ventral side has noticeably blue shade. A large and triangular black marking or hatchet-shaped patch with a bluish tint is present at the posterior half of the body and at the base of the caudal fin, it becomes tapers. Tint red color is seen in the outer rays of the dorsal, anal, caudal and pelvic fins.

Body Size and Lifespan

It is a small sized fish which can grow up to 5 cm in length. Its lifespan ranges from 5-6 years or more if you take proper care.

Quick Harlequin Rasbora Facts

  • Scientific Name: Trigonostigma heteromorpha (Duncker, 1904)
  • Origin: South East Asia
  • Grown-up size: 5 cm
  • Temperament: Peaceful
  • Minimum Tank Size:  15 gallons
  • Tank Level: All
  • Diet: Omnivore
  • Breeding: Egglayer
  • Water pH: 5.5-8.0
  • Hardness: up to 12 dGH
  • Temperature: 73- 82° F
  • Water Movement:  Normal -moderate
  • Lighting need: Normal-moderate
  • Care level: Moderate
  • Lifespan:  5-6 years

Food and Feeding Behavior

It is an omnivore and its food consists of insects, larvae, worms and different types of zooplankton such as Cyclops, Daphnia, and Brine shrimp. It also takes a balance of quality flake or pellet food. You should also offer blanched lettuce or spinach to their diet. It is recommended to feed them 2-3 times every day for making your fish happy.

Housing and Care Facts

It needs at least 15 gallons tank with dimmed light and floating plants. In this case, aquarium plants such as Cryptocoryne and Aponogeton are best suited for your fish. The tank should have good water quality with aquarium filtration system and peat substrates. In this case, water pH should be varied from 5.5-8.0, hardness 8-12 dGH while water temperature should be between 73.0 and 82.0°F. To keep your tank environment healthy, 20-25% water changes should be replaced every other week.


In captive condition, it should be kept in a group with 6 individuals or more due to its peaceful schooling behavior. Suitable tank-mates include barbs, danios Corydoras catfishes, other rasboras, Small characins and Otocinclus catfishes.

Breeding Behavior

It is an egg-laying fish but difficult to breed in captive condition. The breeding tank should be decorated with some aquarium plants (such as Cryptocoryne, Aponogeton) and strong filtration system. Filtration system provides a sufficient supply of oxygen which is essential for hatching of eggs.

In the aquarium condition, the female lays up to 300 eggs underside of the aquarium plant`s leaf. Hatching of eggs occurs within 2-3 days and baby fish become free swimming after 5 days of hatching. For proper growth of baby fish, infusoria, baby brine shrimp (Artemia) and any liquid fry food should be offered.

Male and Female Sex Differences

Sex determination is difficult. Generally, the female is larger with the rounded body while the male body is smaller and slender. Besides these, the body color of the male is brighter than the female.

Concluding Remarks

The Harlequin rasbora is a very popular and attractive aquarium fish among the pet fish keepers. It is a small sized fish with brilliant coloration. It is now available in the pet fish market with rational price. You can also purchase this fish from the online shop. I think it is an attractive and gorgeous fish. You can keep this fish in your aquarium to create more amusement.

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