Harlequin Rasbora - Trigonostigma heteromorpha
 Harlequin – Male. Stefan Maurer

Fish hobbyists love the Harlequin Rasbora — it has a beautiful metallic color and it’s easy to care for. A large school make an aquarium vivid and vibrant with movement.

Harlequin Rasbora: Basics

  • Scientific Name:Trigonostigma 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: R. espei and R. hengeli. However, they may actually 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, so keep them in groups of at least three or more. Harlequins make excellent community fish and will not nip at or quarrel with any other species.


Rasboras are 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 do not occur.


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.

Harlequins are among the more difficult species to breed, however, spawning may be achieved if you provide the proper conditions. Select young specimens and condition them with live foods prior to spawning attempts.

You can breed groups of young Harlequins in a single aquarium. When spawned in groups, keep two males 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, with Cryptocorynes or similar broad-leafed plants in the breeding tank.

Once you prepare the breeding tank, introduce the breeding stock 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.

You may see the male nudging the sides of the female 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 100 eggs may be laid.

When spawning is complete, remove the breeding stock 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 24 hours. Feed fry should infusoria or freshly hatched nauplii, and gradually move to larger foods as they grow in size.

Young reach sexual maturity in approximately six to nine months.

Original article from thespruce.com