Harlequin Rasbora: Care Guide, Breeding, Tank Size & Disease

Harlequin Rasbora: A Brief Introduction

Harlequin rasboras are small, colorful fish native to Southeast Asia. They are popular in the aquarium trade for their attractive appearance and peaceful nature. They are relatively easy to care for and do well in groups, making them a good choice for community tanks.

Harlequin Rasbora Overview

Aquarium fanatics love the harlequin rasbora because it’s very easy to care for. Its metallic color is an eye-catching addition to any home aquarium. It has a reminiscent look of a jokester costume, where the fish derives its name.

A fish swimming in water

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Harlequin Rasbora, sometimes known as red rasbora, are schooling fish. They love to move in small groups and keep company with other similar-sized fish. That’s yet another reason behind their massive popularity.

This small and attractive fish is native to Malaysia, Singapore, Sumatra, and Southern Thailand. However, you can see it in small freshwater aquariums all over the world thanks to its vivid and vibrant colors.

If you have no experience with the harlequin rasbora, this article will help you take care of your fish. We’ll tell you everything you need to know about this beautiful creature and how to make sure that it lives happily in your home.

Information ChartHarlequin Rasbora
Scientific Name: Trigonostigma heteromorpha
Family: Cyprinidae
Care Level: Easy
Temperament: Peaceful
Color: Silvery scales with orange hues
Lifespan: 5-8 years
Size: 1.75-2 in
Diet: Commercial and Live foods
Minimum Tank Size: 10 gallons
Temperature: 73 to 82 F
Water Conditions: Mildly hard
Tank Mate Compatibility: Peaceful

Harlequin Rasbora Appearance

There are 45 different rasbora species, but the Harlequin or Red Rasbora is probably the most popular one. The silver body of the fish is lozenge-shaped with orange-pink hues. However, the exact color depends on the living conditions, including the pH level of the water, the stress levels of the fish, and the characteristics of the original population.

A fish swimming in water

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The mid-section is tall and tapers towards the mouth. The rear half of the body has a black patch that ends at the forked caudal fin. All the fins on the fish’s body are red or dark orange, darker than the rest of the body. 

The color doesn’t remain concentrated in its body and sometimes stretches even to its head and tail. In comparison, the pelvic region and the anal fins are more transparent, which is common in the male and females of the species.

However, an easy way to spot the difference is by looking at their markings. Male fish usually have darker black patches on their bodies. The wedge-shaped marking on their bodies appears more boldly and takes a triangular shape at the bottom. For the females, this marking is much flatter and less distinct.

Lifespan Of Harlequin Rasbora

Harlequins are extremely resilient and can live for a fairly long period. On average, their lifespan can stretch anywhere from five to eight years. However, it’s possible that most won’t live that long. 

A couple of goldfish swimming in water

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If you keep the tank clean, make sure that your fish is safe, and feed it right, your fish will be able to live up to 6 years. The biggest stumbling block most aquarists face is maintaining water conditions that are ideal for the species.

Subpar water can significantly hurt its health and drastically affect its lifespan.

Harlequin Rasbora Size

An average fish will be almost 1.75  inches in size. Some fish will reach 2 inches. That’s still significantly smaller than most of its peers. Harlequins can often grow to be larger when in the wild. Unfortunately, that’s not the case when kept in captivity.

Natural Habitat And Origin

Harlequin Rasboras are freshwater fish. These fish are common in the freshwater rivers of Singapore, Malaysia, Sumatra, and certain parts of Thailand. 

The water of these regions flows regularly through peat swaps. That makes them rich in humic acid, with very little mineral content. The natural habitat of harlequins is also filled with leafy vegetation and floating plants. They feel extremely comfortable in this environment.

After leaving its Asian home, the harlequin rasbora became extremely popular among aquarium owners in the 1930s. Even today, this fish can be found in smaller community tanks because of its low maintenance.

Harlequin Care & Tank Set-Up

If you have a community tank, then you need to add several members of the harlequin rasbora to add more vivid colors to the display. This low-maintenance fish is a good choice for kids and beginner aquarium enthusiasts because you can easily give it a loving and suitable home.

Before moving any new fish to your aquarium, you should keep them in quarantine, separated from all the other fish in your aquarium to make sure that they’re healthy. The harlequin rasbora is grown on farms, but it lives in several fish tanks before it reaches yours.

Naturally, this fish lives in several habitats, including slow-moving rivers and swamp forests. The fish doesn’t mind the bottom’s difference; it can be sandy or waterlogged with soil and dead plants.

This fish prefers top to mid-dwelling in the fish tank. It loves living in heavily planted tanks as the fish enjoys swimming around live plants. You should make sure that there is plenty of swimming space to let the fish roam freely.

Harlequin Rasbora Tank Size And Specifications

If you’re thinking of getting a harlequin rasbora, start with a tank of 10 gallons. Despite its small size, this fish needs plenty of swimming space. This is why you should keep it in an aquarium that is 10 gallons or larger. 

If you choose a smaller tank, you might have to keep the fish in pairs or on its own, which isn’t recommended.

Optimum Tank Size for Harlequin Rasboras

A 10-gallon tank is a size that’s perfect only for a small group of harlequins. It’s important to remember that red rasboras are a schooling species. You can’t just get one. 

So if you’re planning to get a bunch of them, try to get one for every gallon of your tank’s size. Instead of going into all those maths, get a large tank of 20 or even 30 gallons. You can place quite a few of the species in such a tank. You can also introduce other mates to keep them company.

Tank Shape For Harlequin Rasbora

There isn’t any particular tank shape for the species. Although considering they are mid-dwellers, it’s love to swim about, opt for a tank with a wide bottom. The expansive surface will give them plenty of room to swim comfortably.

It will also provide you with several options when decorating the surface. You can imitate the natural habitat of the fish more closely, with plenty of plants and rocks.

Filter Type

Installing an aquarium filter is a smart decision as it removes all the impurities and toxins from the water. In nature, fish have the freedom to swim somewhere else if the water isn’t clean. After you move them to a tank, you should make sure that you’re keeping the fish as healthy as possible by getting rid of all the impurities in the water.

Choose a water filter that removes the toxins chemically and mechanically to eliminate all the solid and dissolved chemicals.

Use a water testing kit to test the water every week. This will help you know if the filter is working properly or not. Keeping a journal of the status of the water is extremely important so you can detect the slightest changes in the water.

There are several treatments that you can buy to increase the water quality in the tank. Make sure to try these if you feel that the water isn’t healthy enough for your fish.

Changing 10% or 20% of the water in the aquarium is a must. Do this weekly to keep the water fresh and maintain ammonia levels under control. Changing 25% of the water once a month is necessary, so your fish won’t suffer from health problems.Install an aquarium heater. This fish can tolerate several temperature changes, but it won’t survive if the fluctuations are too extreme. It’s best to install a heater to keep the water temperature under control.


Cover the bottom of the tank with sand followed by at least 1 inch of dark-colored gravel. The dark bottom will encourage the fish to show their brightest colors, creating a great display in your home. Nevertheless, any rocks you keep at the bottom will rarely attract the fish’s attention because they prefer to swim in the mid-section of the tank.

Add some dried leaf litter to your aquarium. The fish live peacefully among dead leaves from water plants in their natural habitat. Imitating the waters where they come from guarantees that the fish won’t display any weird behavior and will live peacefully for several years.

Water Parameters For Harlequin Rasboras

These fish require little maintenance, but you should make sure that you’re providing them with comfortable living conditions so they can stay healthy and happy.

Water Temperature

The harlequin rasbora lives in a tropical climate where the water is warm. Extremely high or low temperatures are not good for the fish as it lives in water where the temperature is between 73 to 82 F.

Water Flow Rate

Most species of rasboras are extremely vulnerable to poor-quality water. It’s the same case for harlequins as well. The health of the fish is likely to decline in a dirty tank or if the water flow is too high. 

The species prefer slow-moving water. Nailing down this aspect of caring for the fish will definitely promote better health among the pack.

Ph Level

In nature, these fish will live in freshwater. It doesn’t live in brackish water and prefers slightly acidic water between pH levels of 6 and 6.5. The fish is extremely sensitive to any sudden changes in the pH of the water. That’s makes it very important to pay close attention to this.

Water Hardness

The species prefers a hardness level up to 12 dGH. Maintaining a hardness level between 2 and 12 is recommended to keep your fish healthy. Harlequins thrive in harder waters as it’s close to the conditions of their natural habitat.

Harlequin Rasbora Tank Landscape

Best Plants For Harlequin Rasbora Tanks

Add live plants, pieces of driftwood, and rocks to mimic the fish’s natural habitat. This helps the fish get accustomed to the new tank. Keep longer plants to the sides of the tank. This will keep the mid-area free of clutter so the fish can swim freely.

Placing plants around your tank also gives your fish a place to hide when threatened or sleep when tired. So, when picking vegetation for the aquarium, you also need to consider the ones that would be suitable. For this reason, try to go with plants like

  • Anubias
  • Vesicularia
  • Hygrophila
  • Weeping Moss
  • Rotala
  • Ludwigia

Worst Plants For Harlequin Rasbora Tanks

While picking plants for your harlequins, it’s better to skip plants that are toxic or won’t be good for them. Plants like Daphne and Caladium are the worst for your fish, and try to steer away from them.

Lighting For Harlequin Rasbora Tanks

In nature, this fish prefers heavily planted waters, so you need to find a way to diffuse the lighting in the aquarium. Ensure that you keep the aquarium away from direct sunlight, which might disturb your fish.

Feeding Harlequin Rasbora

Harlequin rasboras are omnivorous, and they will feed on a variety of plants and other smaller marine insects and eggs. Providing them with various foods is necessary to keep the fish healthy.

Best Diet For Harlequin Rasbora

This fish has a small mouth, so you should feed them small particles that they can easily swallow. Store-bought food like flakes and pellets contain the essential nutrients to keep your fish healthy. Varying the food texture is a great way to keep the fish interested.

Feeding time can become more interesting if you introduce live food. This will include bloodworms, insect larvae, and daphnia. Due to the movement, the fish will display an interesting activity as they chase their food in the tank.

You can also make your homemade vegetables to keep your fish healthy. They’re unlikely to cause damage to the plants in the tank.

How Often Should You Feed Harlequin Rasbora?

You mustn’t overfeed your fish as this can cause several health issues. Provide your fish with enough food that they can finish in 2 minutes to avoid digestive problems. If you have enthusiastic kids in the house, remind them that the fish should be fed twice a day only. Excess food should be removed from the tank to keep it clean.

Harlequin Rasbora Behavior And Temperament

This breed prefers to swim quickly, but the fish might decide to hide between the plants in the tank. If this happens regularly, then your fish are probably stressed out, and you should try to remove the stress factor to make sure that they’re living comfortably.

The harlequin rasbora displays interesting shoaling behavior, usually moving in groups. Watching the fish for hours is something that most aquarium hobbyists enjoy as they can monitor how the individuals communicate to move in harmony within their groups. Any disturbance in the typical behavior is a sign that the fish aren’t living in perfect conditions, and you, as the aquarium owner, should do something to make sure that they’re safe.

One of the shoaling behavior features is that the fish will prefer to show their brightest colors and their most impressive behavior in larger groups. If you want to add an interesting display to your home, you need to invest in a larger tank.

Are Harlequin Rasboras Lone Or Societal In Nature?

This fish is typically peaceful and enjoys swimming with members of its kind and other species. You need to keep this shoaling fish in shoals of at least 8 to 10 fish. Your fish is likely to feel depressed if you decide to keep it on its own.

Most of the time, the fish can be victims of harassment if they live with bigger or more aggressive species.

Harlequin Rasbora Tank Mates

While choosing other fish to add to your aquarium, you need to ensure that there’s plenty of room for your harlequin rasbora to swim. This will guarantee that your fish will be active and healthy.

Schools of larger numbers are very popular due to their vibrant colors. Nevertheless, you should make sure that there’s enough space for the whole population to live comfortably.

Adding big fish to the tank isn’t a good idea if you decide to keep harlequin rasbora. The attractive vivid colors of the fish will attract predators who might be tempted to take a bite off their colorful bodies.

Ideal Tank Mates For Harlequin Rasbora

Choosing peaceful and sociable tankmates is a good idea to ensure that all your fish are living happily. 

Other small rasboras can also be great candidates for your aquarium.

Bad Tank Mates For Harlequin Rasboras

Avoid adding bigger fish like cichlids. These will most likely view your harlequin rasboras as a delicious meal and will try to attack them. As a rule of thumb, you shouldn’t add any fish that is twice the size of your harlequin rasbora.

Some of the other aggressive fishes that you might want to keep away from your harlequins are:

Breeding Harlequin Rasbora

It’s fair to warn you that harlequins are one of the toughest fish to breed. However, you might have better luck by ensuring the ideal condition for the species to breed. Start by selecting a young member of your tank and feed them a proper diet for a few days. 

Unlike other rasboras, harlequins aren’t egg-scattering spawners. It’s an egg-laying species. It’s relatively better to breed the fish in groups in a single aquarium. Ideally, it’s better to have one female for every two males.

Although many aquarists prefer replicating the species’ natural habitat for breeding, that’s not mandatory. What you must try focusing on are the water parameters. 

  • Try to have a water of hardness not more than 4dGH
  • The pH should be ideally around 6.4
  • Temperature between 76-80℉ is preferable
  • Introduce Crpytocorynes in the breeding tank

The males of the species generally start spawning early in the morning. They try to attract the females to an ideal mating spot. Once ready, the females signal the males to approach and wrap around her.

Harlequins lay around 6-12 eggs at a time. Once fertilized, the eggs rise and stick to the surface of the leaves. During each mating session, the fish generally lays up to 100 eggs. However, the number can climb as high as 300 as well.

After hatching, the fries become free-swimming almost immediately. For the first two weeks and live in infusoria. However, you can substitute infusoria with commercial fish foods as well.

Harlequin Rasbora Breeding Level


Harlequin Rasbora Sexual Dimorphism?

For distinguishing the gender of harlequins, most aquarists look for a few signs. 

Firstly the males of the species are comparatively smaller than the females. They also have a dorsal patch that straightens near their head and becomes round towards the bottom. In comparison, the women lack these distinguishing features on their dorsal patches. Besides, the tip is also less extended in females.

Harlequin Rasbora Common Diseases And Their Treatment

As a freshwater fish, it’s not uncommon for harlequins to suffer from a few diseases in an aquarium. Failing to treat them in time can harm your fish and even lead to premature death. Some of the most common diseases for harlequin rasboras are:

Fin Rot

A slight tussle with other fishes can leave harlequins with fin rot. Having poor tank health can aggravate the situation. One way to avoid fin rot is by ensuring a balanced number of male and female fish in the tank.

White Spot Disease

This respiratory disease is common in the species, and poor tank sanitation is the primary cause behind it. Your fish might start feeling restless or get white spots all over its body. However, you can resolve it easily with proper medications.

Facts About Harlequin Rasbora

  • The fish is found only in freshwater streams
  • They are a popular choice for aquariums but not for fish farming
  • It’s a peace-loving fish with no predatory instinct
  • In the Malay language, it has the nickname “Setem.”

Are Harlequin Rasbora Right For you?

Harlequin Rasbora is an ideal fish for beginners. If you’re looking for a peaceful fish for your aquarium that’s easy to care for; then harlequins are ideal.

The might be a bit fussy about their water parameters. However, considering their irresistible looks and easy compatibility with its tank mates, any enthusiast should definitely get them.


Can Harlequin Rasboras Live With Bettas?

Your harlequin rasbora is a peaceful fish that won’t fight with other fish. It won’t eat any other fish and will continue to live peacefully in a large community.

Bettas are excellent tankmates for your harlequin rasboras. They both live in the same conditions and enjoy swimming peacefully, so you’ll guarantee that you’ll have a beautiful display of active fish that keep on roaming the aquarium for hours. Here are some reasons why harlequin rasboras and bettas are great tankmates.

  • They both come from Southeast Asia. They live peacefully in rice paddies and slow-moving water full of plants.
  • These fish prefer the same types of food and living conditions. This means that you won’t suffer to maintain the tank’s condition to keep them healthy.
  • Harlequin rasboras are fast swimmers. Bettas prefer to swim slowly, so they’re unlikely to attack each other. Even if a betta attacks the harlequin rasbora, it will unlikely catch it.

On very rare occasions, the harlequin rasbora might try to bite on the bettas’ fins. If this happens, you should probably isolate the individual doing this or move your betta to another tank.

What’s The Conservation Status Of Harlequin Rasboras?

As per IUCN, they have a status of Least Concern. That means you can choose to pet them without any fears.

Are They Hardy?

Harlequins are pretty hardy in comparison to other fish species. However, they need clean and clear water for prolonged and healthy life. Otherwise, the species becomes vulnerable to a few diseases.

How Many Harlequin Rasboras Should Live Together?

Harlequins loves to live with others of its kind. In a 10 gallon tank, you can safely place five or even six fish together. However, try to keep a healthy balance between male and female fish. That’s because the males of the species can sometimes engage in a fight between themselves.


Harlequin rasbora is a peaceful and active fish that will bring life to your community tank. Setting up the perfect tank for your fish is easy as you just need to arrange your plants to give the fish plenty of space to swim.

Getting a big tank is recommended so you can add several fish as the harlequin rasbora prefers to live with other members of its kind. It makes a perfect tankmate to other less active and peaceful fish, creating colorful displays that you can enjoy for hours.

Harlequin rasboras are omnivorous and they will feed on a variety of plants and other smaller marine insects, and eggs. Providing them with a variety of foods is necessary to keep the fish healthy.

This fish has a small mouth, so you should feed them small particles that they can easily swallow. Store-bought food like flakes and pellets contain the essential nutrients that will keep your fish healthy. Varying the texture of the food is a great way to keep the fish interested.

Feeding time can become more interesting if you introduce live food. This will include bloodworms, insect larvae, and daphnia. Due to the movement, the fish will display an interesting activity as they chase their food in the tank.

You can also make your own home-made food of vegetables to keep your fish healthy. They’re unlikely to cause damage to the plants in the tank.

It’s important that you don’t overfeed your fish as this can cause several health issues. Provide your fish with enough food that they can finish in 2 minutes to avoid digestive problems. If you have enthusiastic kids in the house, remind them that the fish should be fed twice a day only. Excess food should be removed from the tank to keep it clean.

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