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Family: Cyprinidae, Subfamily Danioninae

Common Name: Harlequin Rasbora

Origin and Habitat: Thailand, Malaysia, Singapore, Borneo and Sumatra. Inhabits slow-flowing forest streams (blackwater) thick with aquatic plants, primarily in peat swamps.

Compatibility/Temperament: Very peaceful, it is suitable for any aquarium of non-aggressive fish. A shoaling fish, it must be kept in groups of at least six, preferably more. The intense colouration of the males will be more evident in groups.

Harlequin Rasbora Diet

In its habitat it feeds on insects, crustaceans, worms and zooplankton. It readily accepts prepared foods, but colouration will be best with some frozen or live foods.


Can attain 2 inches but usually slightly smaller.

Minimum Tank Suggestion

24 inches in length.

Water parameters for Harlequin Rasbora

Soft to moderately hard (hardness below 15 dGH), acidic to slightly basic (pH below 7.5) water, temperature 21-28C/70-82F. Most available fish will be commercially bred, but the fish fares better in soft slightly acidic water and this is necessary for spawning.


One of the most popular of the rasbora fishes, and a good choice for beginning aquarists. It adapts to varying water parameters that are not extreme, is colourful, extremely peaceful, and reasonably active. It prefers a thickly-planted and dimly lit aquarium with a dark substrate, all traits of its habitat sites; swimming room is essential. In such a setup, with soft, acidic water, and fed well with live and/or frozen foods, the fish will readily spawn. Females are rounder than males; the eggs are laid on the underside of leaves.

This fish is sometimes labelled as a "tetra" in stores, but it has no relationship to the true tetra which are characins.

This fish shares a near-identical colour and pattern with two other rasbora, Trigonostigma espei and T. hengeli. The subject species has a deeper body, is more pinkish than the others, and the dark side mark is broader, darker and more triangular. A fourth species in the genus, T. somphongsi, has a dark broad stripe [rather than a triangular mark] that runs laterally below an iridescent stripe; this species occurs in the basin and floodplain of the Menam River in Thailand and is very rare.

Unfortunately some selectively-bred variants (morphs) of T. heteromorpha are sometimes available, and these show a marked degree of physical abnormality and should be avoided.

This species was originally described in 1904 by G. Dunker and placed in the genus Rasbora. Rasbora has been a "catch-all" genus for 138 species of small minnow-type fish. Ichthyologists have (especially during the last two decades) questioned the relationships between many of these species, and Maurice Kottelat and others recognized that the genus was polyphyletic [Greek, "of many races"] which in this instance means it contains species whose last common ancestor is not included. Several species have been transferred out of Rasbora into Microrasbora [now considered a Danio], Boraras and Trignonstigma [these latter two are monophyletic, meaning that they include the ancestor and all descendants], and the species remaining in Rasbora were grouped into clades awaiting further study.

As a result of their study of some of the cyprinid fishes, Kottelat & Witte (1999) erected a new genus Trigonostigma for this and the three closely-related species. This name is from the Greek trigonon (=a triangle or hatchet) and stigma (=a spot or brand). The subject fish, T. heteromorpha, is the type species for the genus. This separation was made on the basis of the spawning method that differs from all other rasbora; in these four species, the female attaches the eggs to leaves, usually on the underside, and the male comes along to fertilize them. Other species of rasbora are egg scatterers. Subsequent studies (Liao 2010, and others) have confirmed this division on the basis of phylogenetics.


Fang, F., M. Norén, T.-Y. Liao, M. Källersjö and S. O. Kullander (2009), "Molecular phylogenetic interrelationships of the south Asian cyprinid genera Danio, Devario and Microrasbora (Teleostei, Cyprinidae, Danioninae)," Zoologica Scripta volume 38 (no. 3), pp. 237-156. [Published first online, 1 Jan. 2009, pp. 1-20.]

Kottelat, Maurice & K.-E. Witte (1999), "Two new species of Microrasbora from Thailand and Myanmar, with two new generic names for small southeast Asian cyprinid fishes (Teleostei: Cyprinidae)," Journal of South Asian Natural History, volume 4 (no. 1), pp. 49-56.

Liao, Te Yu, Sven Kullander and Fang Fang (2010), "Phylogenetic analysis of the genus Rasbora (Teleostei: Cyprinidae)," Zoologica Scripta volume 39 (no. 2), pp. 155-176. [Electronic publication occurred online 2 Oct. 2009.]

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