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Harlequin Rasbora

Trigonostigma heteromorpha

Male Harlequin Rasbora


The Harlequin Rasbora (Trigonostigma heteromorpha, formerly Rasbora heteromorpha) is the most popular of the Rasboras, likely because it is colorful, has an unusual shape, is peaceful, and very hardy.  It has been available to the hobby since 1934.  Other names for this fish are Triangle or Red Rasbora.  It has an attractive black triangle on its’ side with red or pink in its fins and body.  The deep body shape is unusual for a rasbora.  Two other closely related species, T. espei, and T. hengeli appear similar but have more slender bodies and not as prominent a black triangle.  Adults reach a maximum of around 2 inches and they have a lifespan of 5-6 years.  It is a strong schooling fish and inhabits the mid levels of the aquarium.  They are a desired species for a show tank because they school tightly, are active, and have striking colors.  Males are slightly smaller, have more red in their fins and body, and sport a slight gold line above the triangle.  Females have a fuller body and more gold coloration than red.  They come from Southeast Asia and inhabit slow flowing creeks or swampy peat bog pools with much leaf litter and dark tea stained water.  They will eat most any foods, but should be given a variety of frozen, live, and prepared foods for best health.  They seem somewhat susceptible to getting fat and sometimes eggbound if overfed.  They prefer subdued lighting and dark substrate, but want plants in their aquarium, so low light plants such as Java moss, cryptocoryene, or anubias work well.  Ideal temperature for them is 76-80 degrees, with 82 degrees best for spawning.  They will tolerate a wide range of water chemistry as long as it is clean.


Spawning the Harlequin Rasbora can be done by supplying 3 basic needs: 1) Use rain or RO water, 2) High water Temperature, and 3) A suitable spawning plant. 

  1. These fish come from very low mineral content waters.  They are considered difficult to spawn mainly because it is imperative to use mineral free water that is acid to get them to spawn and the eggs to hatch, even though they are otherwise very tolerant of harder water.  I got my first spawning of them in rain water, a peatmoss box filter, and a 2 gallon drum bowl.  After several days, the water was darkly stained and it was difficult to see if they had spawned or not.  A PH of around 5.5 works well.

  2. These fish come from a lowland, warm environment.  Spawning temperature is optimum at about 82 degrees.

  3. They do not just scatter eggs like most rasboras.  They need broadleaf aquarium plants where they can lay eggs on the underside of the leaf by going upside down to lay them.  Their eggs are adhesive, but I observed many times where the eggs did not adhere and fell to the bottom.  There was not any egg-protecting behavior observed, just egg-hunting and eating!  The best plant for them to spawn on seems to be anubias.  They can be spawned in groups or pairs.


The Harlequin Rasbora can lay 100 to 200 eggs.  The eggs are sensitive to light, so keeping them dark is recommended.  Hatching in 18-24 hours, the fry take 3-5 days to become free swimming.  Then they must be fed infusoria for a week or so before they can take newly hatched brine shrimp.  Growth at first is fairly slow and the fry hide very close to and up against the plants.  Later they will venture out and school up.  Attaining full maturity may take 9-12 months.


The Harlequin Rasbora is a common, beautiful, and peaceful fish and I recommend it for most everyone to keep.  Attempting to spawn it is a bit of a challenge, but doable, with the rewards of accomplishment and a large school of attractive fish!

Female Harlequin Rasbora