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Harlequin Rasbora

Rasbora heteromorpha


Female Harlequin

Female Harlequin

Male Harlequin

Male Harlequin

Scientific Name: Rasbora heteromorpha
Other Names: Red Rasbora
Family: Cyprinidae
Origin: Southeast Asia, Malaysia, Singapore, Sumatra, Thailand
Adult Size: 1.75 inches (4.5 cm)
Social: Peaceful, suitable for community tank
Lifespan: 6 years
Tank Level: Top, Mid dweller
Minimum Tank Size: 10 gallon
Diet: Omnivore, eats most foods
Breeding: Egglayer - difficult to breed
Care: Intermediate
pH: 6.0 - 7.5
Hardness: up to 12 dGH
Temperature: 73-82 F (23-28 C)


Of the more than five dozen species of Rasbora, the Harlequin is arguably the most popular of them all. Often referred to as the Red Rasbora, the body is a reddish copper color which is accented by a striking black wedge covering the rear half of the body.

Two other species possessing similar features have been described. However, R. espei and R. hengeli, may in fact be subspecies of R. heteromorpha.



Rasboras are a true freshwater fish, and are never seen in brackish waters. They can be found throughout the lowland waters of Southeastern Asia, where the water is soft and acidic. Harlequins prefer an environment with areas of dense vegetation, an open area for swimming, a dark substrate, and subdued lighting.

Water temperature is not critical, however the ideal range is 74 to 78 F (23 -26 C). The pH of the water should be slightly acidic, in the range of 6.0 to 6.5. They are most comfortable in a school, and should be kept in groups of at least three or more. Harlequins make excellent community fish, and will not nip at, or quarrel with any other species.


Undemanding when it comes to diet, they will readily accept flake, dried, frozen, and live foods. A varied diet will ensure that digestive problems, or susceptibility to disease does not occur.


Harlequins are among the more difficult species to breed, however spawning may be achieved if the proper conditions are provided. Young specimens should be selected, and conditioned with live foods prior to spawning attempts. Males are more slender than females, and exhibit a rounded extension at the bottom edge of the distinctive black wedge covering the posterior of the fish. The black wedge on females is perfectly straight.

Groups of young Harlequins may be bred in a single aquarium. When spawned in groups, two males should be kept for every female. The water must be very soft, ideally no more than 2 dGH. Optimum water temperatures are between 76 and 80 degrees F, and the breeding tank should be planted with Cryptocorynes or similar broad leafed plants.

Once the breeding tank has been prepared, the breeding stock should be introduced late in the day. Spawning will usually being in the morning, and is initiated by the male dancing and trembling before the female. This spawning behavior is intended to direct the female beneath a suitable plant for depositing the eggs. The male may be seen nudging the females sides and rubbing his belly against her back in an effort to move her to the spawning location.

When ready to spawn, the female will turn upside down and rub her belly against the underside of the leaf, signaling the male to join her. The male will approach her while continuing to tremble, then wrap himself around her body and fertilize the eggs as they are released. The fertilized eggs rise and adhere to the underside of the leaves. Over the course of one to two hours, as many as one hundred eggs may be laid.

When spawning is complete, the breeding stock should be removed from the aquarium, as they will consume the fry once they hatch. In water temperatures of 80 degrees F, the eggs will hatch in approximately twenty-four hours. Fry should be fed infusoria or freshly hatched napulii, and gradually moved to larger foods as they grow in size. Young reach sexual maturity in approximately six to nine months.


Readers Respond: Have You Kept Harlequins?

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