Harlequin Rasbora Tank Mates, Care, Size, Breeding & More

Harlequin Rasboras are beautiful freshwater fish that can be found in plenty of tanks all over the world.

I love this species because of its ease of care and stunning appearance. Watching a school of Harlequin Rasboras in my aquarium swimming around just never gets old!

This guide will go over everything you need to know about Harlequin Rasbora tank mates, care, size, breeding & more. Here we will cover habitat, tank mates, their size, breeding, lifespan, and many more!

For home aquariums, Shoaling fish are very popular. It is because of their striking colors and fun group behaviors. To add to your tank harlequin Rasboras are a great example of an easy shooling fish.

They are striking fish that, when added as part of a group, will add a vibrant splash of color to your tank.

These fish are not very demanding. This captivating tiny fish has very low specific care requirements. They’re easy to care for, and as long as they’re fed a simple diet, and their tank is kept clean, they’ll thrive. The perfect match for a beginner.

Learn how to care for these fish including breeding, tank setup, what to feed them, and much more… Keep reading…

Care Level:Easy
Color Form:Silver Body with Orange Fins and Black Patch
Lifespan:5-8 Years
Size:Up to 2 inches
Minimum Tank Size:10 Gallons
Tank Set-Up:Freshwater with Plants and Open Swimming Space
Compatibility:Peaceful Community Aquarium

Harlequin Rasbora Overview

The harlequin rasbora fish (also known as Trigonostigma heteromorpha) is a tropical fish from the Cyprinidae family. It is often referred to as harlequins, For home aquariums, they are one of the most popular rasbora species.

This species is native to Asia and is commonly seen around Malaysia, Singapore, and Thailand. Here they inhabit rivers, streams, and swamp forests that resemble the blackwater habitats of South America.

These small shoaling fish are easy to care for, so you shouldn’t have any problems. They can be looked after by people of experience levels.

This makes them perfect for beginners starting a community aquarium. A small group adds some color and shoaling behaviors to the middle levels of the tank.

They’re peaceful so get on well with other peaceful fish, but they can become a snack for larger species.

You won’t struggle to find harlequins; they’re usually in high demand so most aquarium stores will stock them. You should expect to pay $2-4 per fish.

How big do Harlequin Rasboras get?

Harlequin Rasbora Size

The max size of the Harlequin Rasbora is about 2 inches in length when in captivity. These fish don’t get very large at all when fully grown.

Even still, that’s on the higher end of the size spectrum. Most will only get about 1.75 inches! That makes this species a great fish for small tanks (more on that later).

Temperament & General Behavior

Harlequin Rasboras are very peaceful. They won’t nip on the tails of other fish or show any signs of aggression. In fact, they’re more likely to be targets of aggression rather than causing it.

Their small size makes them an easy target for larger fish. You have to keep your aquarium peaceful with some smaller passive species to keep your fish happy.

For the Harlequin Rasbora, it’s strength in numbers. These shoaling fish will group up and spend their time exploring the habitat together.

They might stray off and do their own thing every once in a while. But for the most part, they stick together and swim throughout the middle and top parts of the aquarium.

They are peaceful creatures; they won’t harass any of their tank mates. If anything, they are more likely to be the victims and will become stressed by boisterous fish.

Most of their time will be spent in the middle layers of the water, rarely journeying to the surface or substrate. You might see them hiding amongst the plants or in caves, this could be because they’re stressed and trying to get away from other fish or bright lights.

When you have a group, you’ll see some shoaling behaviors. The harlequins will move around together, sometimes displaying some interesting behaviors.

On their own, they are quite shy, but when they form part of a group, they come alive and you’ll notice they are much happier and content.

The larger the group, the more impressive their movements and colors will be.

Harlequin Rasbora Appearance

Cherry Rasbora Harlequin Fish

These rasboras rarely grow larger than 2 inches. Since they’re small you can comfortably fit quite a few in one tank.

Their body has a tall mid-section but narrows towards the mouth and forked caudal fin. The rear half of the body has a black patch that narrows with the body and stops at the caudal fin.

This black patch is what gives this fish its name, being similar to the black patterns found on a classic harlequin outfit.

The rest of the body is silver, with tinges of orange. The fins are a darker orange but can vary in color intensity. This depends on lots of factors such as the conditions of the tank, stress levels of the fish, and the population they were bred from.

While these designs aren’t striking on their own, a group can create quite a spectacle. This is the same for other fish too, like neon tetras.

Spotting the difference between males and females can be difficult. Male rasboras tend to possess slightly bigger black patches and have a more rounded portion where the anal fin attaches.

The appearance of the Harlequin Rasbora is where these fish stand out most. The species takes on a diamond-like shape. They are considerably girthier in the center of the body.

The head and backend taper to a smaller point. The tail, in particular, has a more exaggerated taper to accent the tail.

They have a distinct light orange or pink hue. The exact shades vary from specimen to specimen. Not only that, but the colors can change based on water conditions.

The color covers most of the body. This includes the head. It’s concentrated mostly on the top of their bodies. The bellies tend to be light white.

The color doesn’t stop with the body. Usually, it can be found on some fins as well. For many specimens, the dorsal and caudal fins take on a richer color than the rest of the body. It stands out against the more muted tones of their scales.

Meanwhile, the pelvic and anal fins are often transparent.

So, why are these fish called Harlequin Rasboras? Well, it all comes down to the bold patch of black on their bodies. Every fish of this species has a wedge-shaped marking. It’s reminiscent of the triangular patterns found on old-school jester costumes.

The shape starts at the dorsal fin and tapers to a fine point at the base of the tail. The rest of the body is free of any marks, creating a very staunch contrast that stands out.

Male and female fish have slight differences between their markings. Generally, the patch is a little bit larger on male fish. It may also be rounded on the bottom of the triangle.

With females, the shape is completely straight. Another big difference between males and females is size. The females are the dominant-looking ones as the other fish species. They’re larger and girthier than the males.

Harlequin Rasbora Lifespan

The average lifespan of the Harlequin Rasbora is between 5 and 8 years. Most will live until they’re about 6 years old, with good care and genetics determining if they will hit the upper end of that range.

This variance in potential lifespan is fairly significant compared to other freshwater species. These fish are especially affected by water conditions and the quality of their habitat. We’ll get into those specifics in a bit.

Habitat and Tank Conditions

In a wild environment, the harlequin rasbora’s habitat might differ from rivers, the whole way to peat swamp jungles. Though conditions will differ between these habitats, there are a few things that are constant.

The waters in these areas are tropical so the temperatures will be fairly warm and the pH will be near neutral (these fish won’t survive in extreme acidity or alkalinity).

Swamp forests will have waterlogged soil substrates, whereas rivers are more sandy. Planted in the substrate would be plants surrounded by rocks and debris.

Water flow is usually quite slow.

Water Parameters

The perfect habitat starts with high-quality water. When you’re planning a tank for any fish, it’s important that you replicate the same water conditions as the water they are endemic to. In the case of Harlequin Rasboras, you need to replicate the warm blackwaters of Southeast Asia.

Their environments in the wild are pretty unique. The waters are very dark. This is a result of decaying leaves and high concentrations of humic acid.

Despite the dark appearance, the water isn’t dirty. In fact, it’s very low in minerals and has a slightly acidic pH balance.

When you’re preparing the tank, you don’t need to recreate the murkiness of their natural environment, but you do need to stick with the same water parameters.

Here are a couple of important parameters to stick to:

  • Water temperature: 72°F to 80°F (74°F should be your target)
  • pH levels: 6.0 to 7.8 (6.5 is best)
  • Water hardness: 2 – 15 KH (the lower is the better)

In order to maintain consistency in your tank, we recommend performing regular water tests. This will ensure that your Harlequin Rasboras don’t go through any unexpected water changes that can impact their health.

Tank Setup

Harlequins bred for aquariums are grown in environments based on their river habitats, so this is the habitat you need to recreate in your tank.

Start with a soft sandy substrate at the bottom of the tank. You could use gravel instead; this choice is not that important because they will rarely stray down to the bottom of the tank.

Place some plants around the tank for them to hide in, though leave plenty of open swimming areas for them to shoal and swim around in. Any rocks or decorations you add will be purely aesthetical for these fish; they’ll spend most of their time in open water.

You don’t need any specialist equipment; the filter outlet creates a strong enough current and most commonly sold aquarium lights are suitable. You just need to add a heater.

Set your heater between 72-81°F. pH should be 6-7.8 and keep hardness to 2-15 KH.

Setting Up The Inside Of Their Tank

Now, onto the tank decor! Again, the primary goal is to replicate the natural habitat of the Harlequin Rasbora as much as possible.

We always like to start with the substrate. You can use a dark-colored sand substrate or gravel. The choice is yours. These fish will not spend much time at the bottom of the tank, so you don’t need to worry about possible injury from the gravel.

Once you have the base ready, you can introduce some live plants into the mix. Harlequin Rasboras love plants because they offer some protection if they ever feel threatened. Include dense plants like Cryptocoryne or species with broad leaves.

Cryptocoryne plants originated in the same place that Harlequin Rasbora fish are from. Not only that, but they’re soft and leafy enough to swim through.

What Size Aquarium Do They Need?

Tank Size

10 gallons is the minimum tank size for the Harlequin Rasboras. Thanks to their small size, these fish don’t need a ton of room.

This size is perfect assuming you’re keeping a very small group of Harlequin Rasboras. Remember, these are schooling fish. That means you won’t be getting just one of them!.

As a good rule of thumb, you can keep a pair of Harlequin Rasboras for every gallon your tank will hold. However, we always recommend going with larger aquariums if you have space in your home and budget.

Larger tanks of 20 or 30 or 55 gallons will provide your fish with plenty of room to swim around and get comfortable.

Harlequin rasboras need at least a 10-gallon aquarium. Any smaller and there would not be enough space to shoal so you’d have to keep them in pairs or on their own.

How Many Can Be Kept Per Gallon?

Aim for around two per gallon. The larger the tank, the more you can get, and the more impressive a shoal’s display will be.

What fish can live with Harlequin Rasboras?

Harlequin Rasbora Tank Mates:

Before you think about Harlequin Rasbora tank mates, you need to make sure they have enough company within their own species.

How many Harlequin Rasboras should be kept together?

We always recommend keeping a group of 8 to 10 Harlequin Rasboras together. Some aquarists have been successful with smaller groups or even bonded pairs. But these are shoaling fish that do best in a larger group.

Be mindful of your tank size and try to get as big of a group as possible. Just make sure that there’s still plenty of space to swim freely.

You can add a large group to an established community tank as well. The best Harlequin Rasbora tank mates are small and non-aggressive (don’t consider anything else).

Here are a few common species that do very well with these fish:

  • Rummy Nose Tetra
  • Neon Tetras
  • Dwarf Gouramis
  • Cherry Barbs (and other small barbs)
  • Danios
  • Apistogramma
  • Cory Catfish
  • Honey Gourami
  • Small Rasboras
  • Bolivian Ram
  • Mollies
  • Kuhli Loach

As long as their tank mates are small and peaceful, feel free to experiment. This list is only meant to get you started and definitely doesn’t include all your options!

Harlequin rasboras are very peaceful fish. They will stay out of everyone else’s way. This means you’re free to pick other similar fish to keep as tank mates.

You should avoid most species that are larger than double the harlequin’s size as they will probably view them as a snack. Cichlids are likely to do this, especially the larger ones.

Boisterous fish can be a problem too. This species is quite timid so may become stressed if they’re chased by overactive fish. Clown Loaches and Bettas are a couple of species that may harass others.

Small peaceful fish are ideal. Cherry Barbs, Corydoras Catfish, Danios, Dwarf Gourami, Guppies, Hatchetfish, Mollies, Platies, Tetras, and Zebra loaches are just a few good options. Aquarium invertebrates are growing in popularity all the time. You can keep shrimp and snails together with harlequin rasbora; they are unlikely to notice each other.

Keeping Them With Bettas

A lot of people ask about the potential compatibility of Harlequin Rasboras and Betta fish. This combination can definitely work as long as you have the appropriate tank size.

We recommend providing a few extra gallons of buffer space if you want to keep these fish together. Also, keep an eye on how they interact to make sure everyone is getting along.

Keeping Harlequin Rasboras Together

How many Harlequin Rasboras are in a 10-gallon tank?

You can keep harlequins together; in fact, you should keep them in groups of at least four. They’re a shoaling species so do well in the company of their own kind.

The larger the group, the better their displays will be. Only keep an amount that can comfortably fit in your tank though, around two per gallon in at least a 10-gallon tank. You can keep up to 6 harlequin rasbora tank mates in a 10-gallon, sometimes even up to 10 fish together.

What and How To Feed Them?

Food & Diet Recommendations:

Harlequin Rasboras are omnivores. They’re highly opportunistic and will eat pretty much anything they can. This makes things a lot easier for you when it comes to their diet.

However, you do have to make sure that their food is safe to eat. The fish have tiny mouths that aren’t always capable of getting around common fish foods, so keep things as small as possible.

Most owners use tiny pellets or use flaked food as the foundation of their diet. As long as it’s nutritionally balanced, your fish should do just fine with it.

It’s always a good idea to supplement dry food with live food every once in a while. Consider feeding your fish bloodworms, Daphnia, or brine shrimp for a good dose of protein.

As omnivores, these fish will eat a wide range of foods. The main thing to watch out for is the size of the food. Harlequin rasboras have small mouths, so they’ll only be able to eat small particles.

In the wild, this means they’re restricted to foods like plant detritus, small insect larvae, and eggs. Their omnivorous diet means they are opportunistic; they eat whatever comes their way.

The easiest way to cater to their needs in an aquarium is through store-bought foods. At feeding times they will become active and happily take flakes or pellets from the surface. These have been specially designed to contain a range of nutrients.

It’s always best to vary their diet, if not for nutritional purposes, then just to keep it interesting for them.

This can be done with live or frozen foods. Daphnia, bloodworms, and insect larvae are some small examples. Particularly live foods make feeding times more interesting by introducing some movement.

Even though they can eat plants, it’s unlikely so you don’t need to worry about damage. This does mean you can feed them green vegetables though, or even use these to make your own homemade fish foods.

Feed them twice a day, only giving them what they can finish in a couple of minutes. This is easier on their digestive system than giving it to them all in one go.

Any excess food should be removed from the fish tank after eating time to prevent decay.

How to Care for Harlequin Rasboras

Harlequin Rasbora’s care is quite easy no matter how much experience you have, which is great news if you’re a potential owner. These fish are quite tolerant and have no problem dealing with slight fluctuations in temperature.

However, that doesn’t mean that you can just toss them in any old tank! Like any other species, Harlequin Rasboras have their preferences and ideal conditions that help them thrive.

To help your fish reach their full potential in your care, you need to follow the basic guidelines below.

Harlequins don’t get ill very often because they are hardy fish. With proper care, you’re unlikely to experience any problems.

Some common diseases affecting them include dropsy (fluid buildup causing swelling), Ich (White spots over the body), and fin rot.

These diseases, as well as many others, thrive in poor-quality water. A dirty tank is one of the leading causes of disease outbreaks.

Therefore, cleaning your tank is a simple preventative measure to make sure you don’t lose your fish. After cleaning the tank, you might see an improvement in your fish. If not, there are treatments you can buy to help get rid of the disease.

Another factor that raises the likelihood of disease is poor nutrition. If fish isn’t getting all the nutrients they need from their diet, they will be too weak to fight off disease.

Make sure your harlequins are getting a varied diet containing the foods we mentioned earlier. This should give your fish everything they need to stay strong.

If you keep them healthy, they can live for 5-8 years.

Diseases To Watch Out For

One big perk of the Harlequin Rasbora is that they don’t get sick very often. As we mentioned earlier, they’re very hardy and tough. There are no ailments that are specific to this species either.

However, they can still get sick just like any other fish.

The most common disease you should be wary of is Ich. The condition can affect any freshwater fish, and it’s no fun. It’s caused by stress due to poor water conditions.

There are other common freshwater diseases that can impact these fish as well, but they all share similar causes.

You can lower the chance of your fish getting sick by constantly maintaining water conditions. Test the water frequently and do water changes on a regular schedule.

That should keep your fish healthy enough to avoid most of these problems.

Harlequin Rasboras Breeding

Harlequin Rasbora breeding can be a bit tricky. They require pristine conditions to initiate the process. It’s tough but completely manageable with the right knowledge.

First, create a separate breeding tank. It should be relatively large and have the same type of water as the main tank. If you want to provide that added boost of comfort, throw in some peat moss. It can incorporate those humic acids that are available in blackwater environments.

Harlequin Rasbora Eggs

Ensure that there are some broad-leaf plants in your aquarium. The females will use the leaves to keep the harlequin rasbora eggs protected.

Introduce some Harlequin Rasboras when you are completely ready. There should be two females for every male. Then, kick the temperature up to about 80 degrees Fahrenheit. Do this slowly to avoid shock.

Feed some nutrient-rich foods to your fish to prepare them for breeding. Things like bloodworms and Daphnia are good options.

When they’re ready, the female will find a good leaf and call the male over. She will release the eggs under the leaf as the male fertilizes them. The eggs will float upwards and stick to the underside of the leaf.

This occurs several times during the breeding process. Usually, smaller groups of up to 12 eggs are laid. Once the breeding process is over, you may have up to 300 eggs in several groups.

After breeding, remove all of the adult fish. They will eat the fry. The little baby fish will emerge from the eggs after about 24 hours. They will stay on the leaf and consume the egg sac for another 24 hours.

At that point, they will begin to swim freely. Provide very fine infusoria for food. Feed this meal for about 2 weeks before transitioning to powdered fish food. It will only take about 6 months for these fish to reach full maturity.

Unfortunately, Harlequin Rasbora breeds are one of the harder species to breed in an aquarium, however, it is possible. They need to be kept healthy and the conditions in the tank need to match what they’d be used to in the wild.

To encourage spawning, a slightly warmer aquarium temperature (around 80°F) will help. Your fish will need nutritional foods full of protein too; daphnia and bloodworms are good options.

Keep two females for every male. These males will perform a display to entice the female to mate.

You’ll need some broad-leaved plants (such as Anubias Nana) in your tank because once ready to spawn, the female rubs her belly on the underside of a leaf to signal the male. The male will come to fertilize the eggs. These will be attached to the leaf and hatch after 24 hours or so.

The parents will try to eat the fry, so separate the parents from the fry. The fry will be nearly completely clear and feed on a yolk sac for the next 24 hours.

After this, you will have to start feeding them. Newly hatched brine shrimp is one of the few foods small enough to give them. A poor diet can affect development.

Is the Harlequin Rasbora Suitable for Your Aquarium?

These fish are peaceful tank mates, so they do well in most tanks.

To keep these fish happy all you need is a small arrangement of plants.

If you’re looking to breed them then they will need much more attention. Conditions need to be perfect or else they won’t start to spawn.

Add these fish to your tank and you will be rewarded with unique shoaling behaviors and strong colors. The more you’re able to fit in the tank, the more impressive these displays will be. A very big group can compete with some of the most attractive fish in the aquarium industry.


Do harlequin rasboras get along with bettas?

When finding Tankmates in bettafish the rasboras are frequently cited as among the best. Harlequin Rasboras aren’t an exception and there are several interesting reasons as to why these two species make great tankmates.

Will harlequin rasboras eat cherry shrimp?

As with all rasboras, and danios, this fish is tranquil and safe to keep in a tank with other fish (as the other fish are also peaceful) and snails or shrimp, as well as live plants. While it’s safe with adults, the shrimp can feed on shrimp fry.

How big do harlequin rasbora fish get?

Harlequin Rasbora can reach two inches (5 cm) in length.

How many harlequin rasboras can I put in a 5 gallon tank?

This is what makes Harlequins not the ideal choice for a tank of 5 gallons but with regular maintenance and water changes even a small group of more than four fish could be maintained happily.

Do harlequin rasboras lay eggs?

To breed, a female harlequin rasbora swims upside down and then rubs her belly against the lower part of an open leaf or similar structures. This is done to attract the attention of males. Females then lay their eggs. The eggs are sticky and she then ties them to the bottom of the leaf.


Now that you know the fundamentals of Harlequin Rasbora care it’s time for you to pick some up!

These fish are a joy to own and provide endless entertainment without even trying. Trust us, you’ll get sucked into watching your tank quite a bit.

If you’re still a little unsure about this species or how to care for them, send your questions our way. We’re more than happy to help and look forward to hearing from you!

Do you have a group of these shoaling fish? Let us know your experiences in the comments section below…


Dibyajyoti Bordoloi is the creator and author of FishCampRehab.com, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.