Harlequin Rasbora Fish Species Profile

A Great Breeding Fish for Beginners

rasbora heteromorpha

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The harlequin rasbora, a prolific little fish, belongs to the family Cyprinidae. It comes from the Malay Peninsula, Thailand, and Sumatra. It is the most common and the easiest-to-keep member of the rasbora family and was first imported into Europe in 1906, making its way to the rest of the world’s aquariums soon thereafter.

Species Overview

Common Names: Harlequin rasbora, harlequin, harlequin fish, red rasbora, red razor

Scientific Name: Rasbora heteromorpha

Adult Size: 2 inches

Life Expectancy: 3 to 4 years


Family Cyprinidae
Origin The Malay Peninsula, Thailand, and Sumatra
Social Peaceful
Tank Level All levels
Minimum Tank Size 10 gallons
Diet Omnivore
Breeding Egg layer
Care Easy
pH 5.0 to 7.0
Hardness 2 to 12 dGH
Temperature 72 to 79 F (22 to 26 C)

Origin and Distribution

The natural origins of the are the harlequin rasbora are the rivers and streams of the Malay Archipelago, Thailand, Kuala Lumpur, Selangor, Singapore, Borneo, and Sumatra. In the wild, these fish prefer peat swamps and gently flowing areas of forest streams and tributaries where vegetation is thick. Light in these areas is filtered by leaves and tends to be fairly dim.

The water in the harlequin rasbora’s natural setting is extremely soft, and its temperature often rises quite high during the day and drops much lower at night. Currently, most of these colorful little fish have been raised on Florida tropical fish farms and in aquariums so their natural need for very soft water has somewhat abated.

Since the advent of air travel, harlequin rasboras have been imported by the tens of thousands from their native Malaya. In spite of constant demand, the source in their natural home is never depleted. They swarm in great numbers in pools in Malaya; even when all are caught in a large net, the pool fills up with fish again in what seems like weeks.

Colors and Markings

The appearance of the harlequin rasbora, with a dark triangular patch extending all the way back from the front of the dorsal fin, is very distinctive. The silvery tone of the rest of the body may be broken with yellow or reddish markings, which has resulted in this species' nickname, the red razor. Males tend to be brighter in color and have slimmer bodies than females. The female has a rounder lower profile and, at breeding time, becomes quite plump.


In nature, the harlequin rasbora does not usually tolerate contact with fish of other species; if you keep them in a community tank, keep at least five or seven (or more), and make sure there are plenty of places to hide. Choose small, peaceful tankmates that are unlikely to agitate or attack them. In a peaceful tank, your harlequin rasboras will be happy community members and will not bother any other fish in the tank.

Shoaling fish should always be kept in odd numbers of three, five, seven, or more to ensure that there will be odd numbers of males and females. This encourages competition and interest in the shoal, keeping them together, rather than having them pair off in different areas of the aquarium.

Harlequin Rasbora Habitat and Care

Harlequin rasboras prefer slow-moving, highly vegetated, peaty waterways in the wild. In captivity, start with a dark, sandy or gravely substrate and add some leafy detritus. Also, include plenty of live plants, rocks, and driftwood. Be sure to keep the plants toward the back and sides of the tank to leave room for an active shoal of fish. Keep lights relatively dim, and add some floating vegetation as well.

In a well-planted aquarium with other docile community fish, harlequin rasboras have been known to breed and live alongside their young with little or no assistance from the aquarist. This is indeed a fun fish to breed, offering beginners and experts alike very satisfying results.

Harlequin Rasbora Diet and Feeding

Rasboras are not picky eaters and enjoy a varied diet of high-quality flakes or granules and live foods such as daphnia and artemia. You can supplement this diet with meaty options such as freeze-dried bloodworms or tubifex worms. Rasbora also enjoy frequent treats of fresh vegetables.

Gender Differences

Male and female rasboras are roughly the same size, but the sexes are easily distinguished. Males have much more red coloring in the dorsal and caudal fins as well as in the caudal peduncle region. The female is more of a golden hue, and when full of roe, her belly is deeper than that of her mate.

Breeding the Harlequin Rasbora

To breed harlequin rasboras, first set up a separate breeding tank that includes broad-leafed cryptocoryne plants, the rasbora's favorite location for laying eggs in its natural environment.

Next, place a well-conditioned adult male with a female, heavy with roe, in the breeding tank late in the day. Courtship begins early the next morning; it is initiated by the male and includes the usual fin-flaring and dancing. The pair starts swimming together, eventually moving under a suitable broad leaf of a plant. Here they turn upside down and deposit a few eggs. They move off to court again before coming back to spawn again, which will probably take place on the same plant, or even the same leaf.

A healthy pair will have deposited 25 to 100 eggs. Rasboras are not avid egg eaters, but they will eat some of the eggs occasionally. Therefore, it's a good idea to remove the parents as soon as breeding has concluded.

The fry hatch in about 24 hours and are free-swimming on the third day. At this point, feed them infusoria or liquid fry food or an egg yolk squeezed through a cheesecloth for the first week. Then, wean them slowly onto baby brine shrimp and commercial dry ground fry food. Harlequin rasboras grow extremely fast and have reached adult size within three months if fed well and often. Add a sponge filter after the first week, and change 10 percent of the water every week after the first month.

More Pet Fish Species and Further Research

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