Harlequin Rasbora – A Complete Guide (Care, Diet, Facts)

What characteristics make a good beginner fish? Ease of care would rank towards the top. Bright colors and a distinct appearance also matter. Good health is important as well, along with affordability and a demeanor that is tolerant of other fish in a tank.

For freshwater fish keepers, the Harlequin Rasbora (Trigonostigma heteromorpha) may be just the species to acquire and add to their tank. Also known as the Red Rasbora, this peaceful, schooling fish is an easy pet to maintain. At $2-4 at most pet or fish stores, they make a terrific starter fish, or an easy addition to a tank with an already established population.

The Harlequin Rasbora is native to southeast Asia, in particular Thailand and Malaysia. They can be found in slow, shallow streams, where the waters are consistently warm. These streams often flow through peat forests, where the leaves fall from trees and never fully decay. This means that the Harlequin Rasbora is quite tolerant of different water parameters.

It is one of roughly 84 species of rasbora, but thanks to its appearance, generally good health, and adaptability, the Harlequin Rasbora is perhaps the most popular among home aquarium owners. Most fish stores, and general pet supply stores, will carry this rasbora in stock.



The Harlequin Rasbora is a fairly small fish, reaching only two inches (5 cm) in adulthood. Their bodies are thin and fairly long for their proportions. From the side, the rasbora has a distinct teardrop profile, with its body tallest at the dorsal fin, and then tapering from there along the tail.

Its fins generally have a splash of color around the edges, before giving way to a translucent white. The tail fin is most notable, as it is fairly long, with a sharp notch in the center.

The name of the Harlequin Rasbora is inspired by the reddish tint it acquires in most water conditions, and the triangular black spot that begins just behind its dorsal fin. This spot starts as a vertical line and follows the shape of the fish’s body. It then tapers to a point at the start of the rasbora’s tail fin.

Its black spot is also how it can be told apart from other rasbora, particularly the lambchop rasbora, which also has a similar black marking on its body. The lambchop rasbora’s spot begins in the same place, but does not extend to the tail in a triangular shape. Instead, it cuts in vertically below the caudal fin, and then follows a horizontal line to the tail fin.

The rasbora’s prominent crimson and black coloration etch a sharp contrast to most other freshwater fish. Their shoaling behavior only adds to their visibility, allowing them to stand out in any tank setup.

Male and female harlequin rasbora can be distinguished by looking at a few specific details in their appearance. Females often have slightly taller bodies when seen in profile. Viewed from the front, the males appear to be more thin. The wedge shape of the male’s black spot is also slightly different than the female’s. The male’s spot will be more rounded at the bottom.

Over the years, breeders have produced several color variations on the harlequin rasbora’s crimson and black hues. The gold harlequin retains the signature black spot, while the rest of the body is a golden or copper shade. A primarily black variant is known as the black harlequin rasbora. There is also a blue harlequin rasbora, which has a soft blue hue to its body.


The Harlequin Rasbora is one of the easiest community fish to keep. They have a social and peaceful nature, and enjoy being in large groups. They are a schooling fish, so the larger the shoal that you keep, the more active and bold they will be. Due to their small size, most tanks can accommodate groups of 10 or more.

The rasbora prefers swimming in the middle of the water column, but will explore the surface and bottom of your tank as well. The more plants and rocks they have to enjoy, the more active they will be. As they explore the tank and its features, they can be playful with both each other and their tank mates. Males especially may seem more extroverted, as they seek the attention of females.

Due to their small size, they can be timid in solitude, or even in small groups. An individual fish will seek shelter when stressed, and may be more prone to harassment from other fish in your tank. To ensure the harlequin rasbora’s health, it is extremely important to provide the harlequin rasbora with enough company of its own kind.


The Harlequin Rasbora is an excellent community fish. It shows no instinct to harass or nip at other fish, and is also peaceable towards its own kind. This allows owners to keep the rasbora in larger schools. These larger shoals make their crimson and black colors all the more visible.

As a peaceful, non-aggressive fish, the rasbora is susceptible to being preyed upon by more aggressive species. Even semi-aggressive larger fish may be drawn to their bright colors and make them a snack.

For their safety, keep them with fish of similar temperaments. Many species of tetra will be suitable tankmates, as will gouramis, small catfish, and other rasbora species. The safer the harlequin rasbora feels, the more apt it is to swim about in direct light and flash its colors.


The Harlequin Rasbora is an enthusiastic eater. They can be sustained on an omnivorous diet, and will be happy to nibble at food provided for other tank mates. Flakes and pellets make a suitable food source for them.

Meaty foods, such as brine shrimp, mysis shrimp, and blood worms, may help to bring out the rasbora’s vibrant colors. Frozen pellets are also a welcome treat.

For breeding purposes, insect larvae and daphnia should be included in their meals. To replicate their natural food sources in the wild, leafy plants such as kale, spinach, chard can be given to them. They also may enjoy zucchini and other soft vegetables.

Feed them 1-2 times each day, and your harlequin rasbora should thrive.

Tank Setup

The Harlequin Rasbora is a hardy, healthy species, and can handle certain variations in its water parameters. Nevertheless, there are a few key guidelines to follow.

Your tank’s pH levels should be relatively low, and kept at a consistent number. Experts recommend a level between 5.5 and 8.0, with guidance towards the lower end of that range. Their natural environment produces a fairly soft water, so hardness should also be low to medium, between 2 and 15 dH. Keep your ammonia and nitrite levels as low as possible.

The forests of Southeast Asia can be warm, so the fish can handle fairly high temperatures. Keep your tank in a range of 72 to 82 degrees fahrenheit (approximately 25 – 28 degrees celsius). A tank heater that provides a consistent temperature is recommended.

While they are not a large fish, their schooling behaviors mean that a microtank environment is not ideal. Consider a tank of at least 20 gallons or more. This will allow them room to remain active, as well as to seek shelter if they are stressed.

These rasbora evolved in slower moving streams and pools, so moderate water movement is all that they require. As long as you purchase an appropriately sized filter for your tank, that should be all that the rasbora needs  for sufficient water flow.

Tank Environment

The Harlequin Rasbora will enjoy features that best replicate their natural environment. The water parameters mentioned above are the first step in creating their aquarium habitat. Plants, rocks, lighting, and substrate are other items for an owner to keep in mind.

Broad, leafy plants that provide shelter and shade will be appreciated by the harlequin rasbora. Consider selecting plants that will grow up through the water column and reach the surface. They will also enjoy other elements like floating plants, driftwood, and bogwood.

Rocks also provide them both with shelter and places to explore. Porous or arched rocks will allow them to swim in and out of tunnels and caves. Try to select softer rocks without sharp edges to avoid any accidental jostling.

A soft bottom to your tank will also mimic the pools and slow streams of Southeast Asia. Dark sands and dirt, or driftwood, will provide maximum contrast to the harlequin rasbora’s bright colors, and allow the school to shine out even in low light.

The tall forests of their natural habitat provides considerable shade for them in the wild. Low, soft lighting will help to recreate this for them. The fish may be stressed by light that is too harsh or bright, so be sure to pay attention to their energy and activity.


Given the right conditions and preferable water parameters, Harlequin Rasbora are capable of breeding in captivity. If your ambition is to encourage your fish to spawn, keep a close on your all of the levels in your tank. Spawning does not happen without work, however.

Experienced breeders have a variety of suggestions aimed at creating the right circumstances for the rasboras to reproduce. Younger fish are more likely to mate together, but you can maximize your chances by providing two females for each male.

You can also use peat as a source of filtration for your aquarium water. This simulates the conditions that the rasboras would find in the wild. It is also the only way to introduce the humic acids that the fish are accustomed to.

You will likely have better success if you keep a separate spawning tank, furnished with plants and rocks. Place the male and female fish in the spawning tank. If they are interested in mating, the male will begin to dance and tremble, and the female will move towards the leaves of the plants.

She then will release her eggs, and the male will fertilize them as they drop and cling to the leaves. This can continue for 1-2 hours, so be patient and watch for her to finish laying her eggs. You should remove the breeding fish from the tank once she is complete, as the harlequin rasbora have a reputation for eating their eggs in captivity.

Try to keep the water temperature in your spawning tank at 80 degrees.The eggs should develop on their own, and begin to hatch after about 24 hours.

For the next 12-24, the fry will remain on the leaf. After this period, they should begin swimming freely. They will eat infusoria, which are microscopic organisms that are essentially the equivalent of freshwater plankton. Infusoria can be found at specialty aquatic supply stores. Ambitious fish keepers can also cultivate infusoria on their own.

Juvenile rasbora reach maturity around 9-12 months of age. They will be able to spawn until they are around 3 years old.

The Fish for You?

Aquarium owners prize the Harlequin Rasbora for a number of reasons. Their coloration and shoaling behaviors make them a prominent member of any adequately large tank. With the right plant and substrate in your tank, their crimson and black colors be all the more visible.

As a smaller fish, they do not require constant feeding, or large amounts of food. They coexist well with other species, and are relatively adaptable to most tank setups. As long as their water parameters are kept consistent, they have good health and a 6-10 year lifespan.

The Harlequin Rasbora is an easy fish to keep, and as such may be ideal for new freshwater fish keepers. More experienced aquarium owners may enjoy the challenge of creating a spawning tank, and breeding select pairs from their shoal.

The rasbora is also available at most pet stores for $2-4, with select colorations also available through aquatic pet stores and special dealers. This makes keeping a school of 10 a fairly affordable endeavor. Their peaceful but curious temperaments and flashy colors make them a joy for any owner.

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