Harlequin Rasbora (Trigonostigma Heteromorpha): Ultimate Care Guide


Common Name(s)Harlequin Rasbora
Scientific NameTrigonostigma Heteromorpha
OriginThailand, Malaysia, Singapore, Sumatra
Temperature72F to 81F
Sizeup to 2 inches
Minimum Tank Size10 gallons
Food & DietOmnivorous
Lifespan5 to 8 years
Water pH6.0 to 7.8
Tank MatesTetras, Corydoras, Barbs, and Danios
BreedingEgg scattering spawner
DiseaseCommon diseases include fin rot, Columnaris, Ich, and Dropsy

Harlequin Rasbora Facts

  • Harlequin Rasboras are a shoaling species of fish. This means that they prefer to swim together in groups. They exhibit all of their social behaviors by shoaling. They eat together and explore their tank together. The more space you can provide Harlequin Rasboras with, the more of these interesting behaviors they will display.
  • Make sure you have a secure lid on your tank. Harlequin Rasboras are active fish that will easily startle and jump right out of their tank.
  • Harlequin Rasboras are a shoaling fish that have been know to shoal with other species of Rasbora.
Harlequin Rasbora (Trigonostigma Heteromorpha)
Harlequin Rasbora (Trigonostigma Heteromorpha)

Harlequin Rasboras have very distinctive markings that make them easily identifiable from other Rasbora species. Harlequin Rasboras have a round shape to their bodies with short fins. They have a silvery sheen to their bodies that seem to have an orangish shine emanating from its core. Harlequin Rasbora male and females have a black triangle shape that extends vertically from their dorsal fin to their caudal fin. The tip of the black triangle ends at the tail of the Harlequin Rasbora.

Male and Female Harlequin Rasbora

Male and female Harlequin Rasboras look very similar to one another, but they can easily be distinguished from one another when they have reached full maturity. The male Harlequin Rasboras grow to have more red, and deeper orange colorations on their fins. The female Harlequin Rasbora will also appear to be more rounded in her belly area when she is full of eggs and ready to spawn.

Harlequin Rasbora Size and Lifespan

Harlequin Rasbora can grow up to 2 inches in length at full maturity. If cared for properly, Harlequin Rasboras can live anywhere from 5 to 8 years in captivity.

Harlequin Rasbora Care

The minimum tank size for Harlequin Rasboras is 10 gallons, but if you have the space, more room is always welcome. Harlequin Rasboras are active little fish that spend their time shoaling together. By giving them the most space possible for their aquarium, you will be able to more easily see their unique behaviors that make them such a popular choice for home aquariums.

In the wild, Harlequin Rasboras inhabit waters that have much more constant water parameters. In captivity, Harlequin Rasboras have been bred to withstand a much more varied temperature of around 72F to 81F, and 6.0 to 7.8 pH. Harlequin Rasboras are small and water cleanliness is important to their health and happiness. It is a good idea to invest in a quality filter for their tank. As well as providing them with clean water, the filter also adds just enough water movement to mimic the slow moving waters of the Harlequin Rasbora’s natural environment.

How Many Harlequin Rasbora Will Fit in a 10 Gallon Tank?

Harlequin Rasboras are a shoaling fish that need to be housed in groups of at least 6. A group of up to 6 could fit in a 10 gallon tank, but that is the minimum size of tank that they should occupy. They are an active fish, and if you have the space to give them a larger tank and offer them more room, the fish will be able to show off their interesting behaviors, and you will have a much better view of it.

Food and Diet

In the wild, Harlequin Rasboras inhabit small streams and waterways. They can also be found in peat moss swamp forests. They are opportunistic feeders. This means that they are not picky eaters and will eat the detritus that falls down from the trees and plants around them, as well as insects, larvae, and worms. In captivity, you can expect them to readily accept foods with the same amount of enthusiasm. Even though you will see them eating whatever you give them, it is still important to offer Harlequin Rasbora a varied diet of high quality foods.

The most accurate way to recreate their diet in the wild would be to offer your Harlequin Rasbora flaked plant foods regularly, and frozen meat or live meat foods every once in a while. Make sure that you are choosing foods that can fit in the Harlequin Rasboras small mouths. Bloodworms are too big.

How to Setup a Tank for Harlequin Rasbora

When setting up a tank for Harlequin Rasbora it is best to try to stick to a setup that closely mimics their natural environment. In the wild, Harlequin Rasboras live and thrive in the lowland waters of southeast Asia. These waters are densely planted with vegetation and have lots of open spaces for them to explore and roam. These waters are also darkened significantly by overhanging plants and dark, muddy substrate.

When choosing substrate for a Harlequin Rasbora tank you can’t go wrong as they will mostly leave the substrate, plants, and decor alone. Just be sure to choose something that is dark in coloration. For plants, choose a thicker variety such as Cryptocoryne or Aponegeton. Plant these plants in dense little groups to leave as much open space for Harlequin Rasbora to shoal as you can. Harlequin Rasboras do not need anything more than a regular aquarium filter for water flow as well. They don’t enjoy much current, and the flow from the filter is more than enough to keep them happy.

What Does a Natural Habitat for Harlequin Rasbora Look Like?

Harlequin Rasbora’s natural habitat is darkened by the substrate, densely planted vegetation, and low lighting due to overhanging plants and foliage. They inhabit the dark, slow moving waters of southeastern Asia where they shoal together in the open spaces as they search the waters for food.

Do Harlequin Rasbora Like Current?

Harlequin Rasboras inhabit slow moving waters that do not provide their natural habitat with a lot of fast moving waters or current. A regular tank filter will provide your Harlequin Rasboras with enough water movement to mimic what they are used to in the wild as well as keep their water clean.

Tank Setup

When choosing decor for a Harlequin Rasbora tank, you should choose items that will closely mimic their natural environment in the wild. Harlequin Rasboras are fish that shoal together, and they will not usually bother any of the objects placed in your aquarium in favor of free swimming while looking for food in the more open spaces of the aquarium.

The Harlequin Rasbora’s natural environment is darkened by thick foliage, and overhanging plants, rocks, and driftwood. You will also want to make sure that you have a secure lid for your Harlequin Rasbora tank as they are easily startled and will jump out of the water.

Harlequin Rasbora Tank Mates

The best tank mates to choose for Harlequin Rasboras are other fish of the same species. Harlequin Rasboras are shoaling fish. This means that several Harlequin Rasboras live and travel together in the same group as part of their social behavior. Other compatible tank mates for Harlequin Rasboras would be some Tetras, Corydoras, Barbs, and Danios. You will want to make sure to monitor any fish that you put together in a community setup. This is to make sure that they are getting along well together. It is a good idea to frequently monitor them at first so that you can identify and correct any problems as they arise.

The worst tank mates to house with Harlequin Rasbora are any fish that are larger, territorial, or would potentially see Harlequin Rasboras as food. Fish to avoid in a Harlequin Rasbora tank include some Gouramis, Cichlids, Loaches, and some of the more aggressive Bettas.

Harlequin Rasbora and Betta

Harlequin Rasboras can be great tankmates for some species of Bettas as they are both hardy fish that enjoy many of the same water parameters and foods. Betta Fish are territorial and will often chase away other fish that wander into their territory, but Harlequin Rasbora shoals are quick enough moving that they will not get in the way of the Betta. One small 10 gallon tank will house up to 6 Harlequin Rasboras with one male Betta. The tank would need an additional 5 gallons for every 1 fish added to the community tank.

Are Harlequin Rasbora Schooling Fish?

Harlequin Rasboras are schooling and shoaling fish. They do this as a way to provide themselves with protection and safety. By grouping together, it makes them safer from predators.

Therefore, they prefer to live its life as a part of a grouping of other Harlequin Rasboras. In the wild, Harlequin Rasboras can travel in a much larger grouping than they do in captivity.

How Many Harlequin Rasbora Should Be Kept Together?

The minimum schooling size that Harlequin Rasboras should be kept in is 6. This small grouping happens most frequently in captivity. In the wild, Harlequin Rasboras shoal together in much larger groups.

Will Harlequin Rasbora School with other Fish Species?

Harlequin Rasboras will school with other Rasbora species, and owners of community tanks that contain multiple types of Rasboras have reported this happening. Schooling is still a behavior that is mostly unknown by science, but it could potentially be explained by their peaceful nature and similar social behaviors.

Harlequin Rasbora Breeding

Harlequin Rasboras are extremely difficult to breed in captivity. If you are planning on breeding Harlequin Rasboras in your home aquarium, you may want to consider setting up a dedicated breeding tank. The difficulty in breeding Harlequin Rasboras at home mostly lies within the specific water parameters that they require to spawn. An ideal breeding tank setup would be densely planted, and also have the low light that mimics the waters in which they are endemic.

How to Breed Harlequin Rasbora

When Harlequin Rasboras are ready to spawn, you will be able to visibly see that the female is more rounded and full of eggs. This is the time to move her to the breeding tank. Female Harlequin Rasboras prefer to spawn in or around Cryptocoryne plants.

Place the mature male and female Harlequin Rasboras in their breeding tank late in the day, and they will begin courtship early in the morning. The courtship of the Harlequin Rasbora begins with a short dance. The male and female will spend a small amount of time together, and you will be able to see the fin flaring and dancing like movements.

When the two are ready, they will find a large leaf to go under. The eggs are laid upside down and deposited onto the leaf. The pair will swim away to begin this process again, but they will return, most likely, to the same leaf to deposit more eggs. A healthy pair of Harlequin Rasboras can lay anywhere from 25 to 100 eggs in one spawning.

Do Harlequin Rasbora Lay Eggs?

Harlequin Rasboras deposit their eggs on the underside of leaves, or around the same plant in one spawning.

How  Many Eggs Do Harlequin Rasbora Lay?

In the right conditions, with healthy fish, a breeding pair of Harlequin Rasboras can lay up to 100 eggs in one spawning. This number is largely dependent on the female Harlequin Rasbora. Even though they are not known to actively seek out their eggs or fry to consume, Harlequin Rasbora parents have been known to consume their own offspring. This makes it a good idea to remove the parent fish from the breeding tank once they have completed spawning.

It takes a Harlequin Rasbora egg about 24 hours to hatch, but they do not become free swimming until they are roughly 3 days old. It is at this time that you will want to start introducing food to the Harlequin Rasbora fry. Make sure that the food you choose is small enough to fit into their mouths. Harlequin Rasbora fry grow extremely fast. If they are fed well, and maintained correctly, they can reach their full adult size at just 3 months.

Harlequin Rasbora Disease

Harlequin Rasboras are susceptible to many of the same diseases and ailments as other freshwater fish. They become more susceptible to disease if they are not cared for properly. It is important to establish a regular cleaning routine. Water changes are essential to keeping Harlequin Rasboras healthy and happy. Here is a short list of some of the most common ailments that can affect Harlequin Rasboras.

Fin Rot – Fin Rot is an ailment that has symptoms that show up exactly like it sounds. You will see deterioration of the fins of the fish. Fin Rot is a bacterial disease that is fairly common and preventable. Poor water quality is the main contributing factor to fish being affected by Fin Rot.

Columnaris and Ich – Columnaris is a common Rasbora disease that is also caused by a bacteria. This bacteria is often mistaken for other common ailments such as Ich. Both Ich and Columnaris both show up as bleached looking white patches on the skin of the fish. This bacteria is mostly caused by poor water quality, and can also be prevented with regular cleaning and water changes. Both ailments are potentially curable if caught early and treated. Note that both infections are contagious and you will want to quarantine your fish away from others until they are healthy again.

Dropsy – Dropsy is a disease that causes bloating and swelling in the abdomen of the fish. You can identify Dropsy by observing your fish. A fish affected with Dropsy will have a swollen belly, pale gills, and become lethargic. There is a treatment for Dropsy that could potentially save your fish if it is caught early enough. You should quarantine any new fish away from others to prevent accidental spread of these common diseases and ailments.

Where Can I Find Harlequin Rasbora for Sale?

If you are looking to purchase Harlequin Rasboras for your home aquarium, you can purchase them in pet stores or online. You will want to make sure that you are purchasing them from a reputable source so that you are assured to get the correct fish. You can expect to pay anywhere from $2 to $4. Keep in mind that you want to keep them in a grouping of at least 6 since they are a shoaling species.

Harlequin Rasbora VS Neon Tetra

Harlequin Rasboras and Neon Tetras make great tank mates as they both have the same water parameter needs and both fish enjoy similar dietary needs as well. Harlequin Rasboras can be safely housed with most species of Tetra as they are a more peaceful fish with similar size.

Harlequin Rasbora VS Lambchop Rasbora

The main difference between Harlequin Rasboras and Lambchop Rasboras is their coloration. The Harlequin Rasboras have a more pinkish brown tone to their bodies, while the Lambchop Rasboras have a more orange coloration. Other than their coloration, both of these fish are similar in size, and shape. They both enjoy the same dietary needs, and have the same social behaviors.

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With decades of collective fishkeeping experience, we are happy to share the fish care tips that we've picked up along the way. Our goal at Fish Laboratory is to keep publishing accurate content to help fishkeepers keep their fish and aquarium healthy.

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