Harlequin rasbora

The Harlequin rasbora is a common and popular aquarium fish that can be found in most well stocked fish stores. It is a small and friendly fish that can be kept in community aquariums with other small and friendly species. It should not be kept with small and/or aggressive fish. There are three common variations of this species in the trade: the normal wild type, the black type and the golden type.

The Harlequin rasbora originates from Thailand, Eastern Sumatra and the Malaysian Peninsula where they live in rivers and streams located in peat forests. They are typical blackwater fish that prefers soft and acidic water. It is a shoaling fish that should be kept in a shoal of 8 or more fish.

This species is one of three species that are often confused with each other and sold under the wrong names. The other two species are the Glowlight Rasbora (Trigonostigma hengeli) and the lamb chop rasbora (Trigonostigma espei). The Glowlight rasbora and the lamb chop Rasbora are both sold as false harlequin Rasbora which should tell you how similar to this species they really are. It is possible to tell the species apart if you take a closer look at their colorations and patterns. The Harlequin Rasbora is higher (stalkier) than the other two species. It has a pink to bright red colour. The black spot is located close to the triangle on the back of the body and the spot as a blue hue to it. The Harlequin Rasbora also has a larger triangle then the other two species. The Lambchop Rasbora has a bronze pink colour. The Glowlight Rasbora is butter coloured and has a faint orange line above its black spot. This line is not present in the Lambchop Rasbora.


The Harlequin rasbora is one of the hardiest rasbora species kept in aquariums and it will adapt to a variety of different conditions. It is however best kept in pH 6-7.8 and the water should be soft to medium hard (max 15°dH). The species has much more particular water preferences if you want it to breed. It is a black water species and prefers water that has been filtrated through peat although this is not mandatory.

Low filtration is enough for this species but it tolerates more powerful filtration than many other rasbora species. Use enough filtration to keep the water clean.

The aquarium where you house your Harlequin rasbora should be densely planted along the sides and back while leaving open areas in the front for the Harlequin rasboras to swim. They seem to prefer plant species that are found in their native water such as Cryptocoryne and Aponogeton species, but other similar species will do as well. They will need broad leafed plants to spawn. You are free to use other plants as well as long as plants of this type are included in the decoration. Use plants and bogwood to create shaded areas where the fish can seek refuge if spooked and to rest. Just like many other rasbora species, the Harlequin rasbora prefers dimmed light and a few floating plants on the surface in the open area is therefore a good idea. A dark bottom substrate is recommended.

As mentioned above, this species should always be kept in groups consisting of at least eight specimens, preferably more.

The Harlequin rasbora is easy to feed and will usually accept most food types including flake food when kept in aquariums. It is important to give them a varied diet consisting on frozen and live food as well as vegetables. The basis of their diet can be flake food but they should not be fed flake food exclusively.


The Harlequin rasbora can be hard to sex but the females are usually a little bit larger and rounder than the males. The males are usually smaller and more slender. It is however hard to say for sure using this method. What looks like a male can be a small unconditioned female and what look like a female can be a fat male.


The Harlequin rasbora is a hard species to breed. It requires very soft acidic water. The water hardness should not be higher than 1.5 to 2.5 (4) DH when trying to breed this species. The pH-value can be kept around 6.0 and the temperature should be at 28°C (82.4°F).

Unlike many other rasbora species the Harlequin rasbora is not an egg-scatterer; it will deposit its eggs on the underside of a broad leaf. In the wild it is usually a cryptocoryne leaf. The spawning usually takes a long time and they might spawn for days before mating finally takes place. The eggs are deposited 6-12 at a time and a total of up to 300 eggs can be deposited. A typical mating results in 80-100 eggs. Once fertilization has taken place you will need to remove the parents as they will eat their own eggs and fry.

When the parents have been removed the water level should be lowered to 10-15 cm (4-6 inches), unless this would not put any eggs above the water line. Harlequin rasbora eggs hatch after 18-36 hours and the offspring will become free swimming 3-5 days after that. The fry are 3 to 4 millimetres long and need to be feed infusorians or other small food. They will be large enough to accept newly hatched brine shrimp after 7-14 days. The fry grows rather quickly, much quicker than many other rasbora species. The fry will look as miniature adults after 8-10 weeks.