Harlequin Rasbora tank mates (11 interesting facts)

In this article of “Harlequin rasbora tank mates,” we will cover the characteristics, behaviour, habitat and breeding of harlequin rasbora fish. We will focus on adjusting the harlequin fish in your tank and its care.

Harlequin Rasbora tank mates

Harlequin rasbora is peaceful and not predatory as long as they are not adults. They do not eat other species as long as they are not adults. Harlequin rasbora tank mates are betta fish, neon tetra, cardinal tetra and small barbs. Harlequin rasbora is a shoaling fish and can be kept in a school of 8 to 10 mates.

The best harlequin rasbora tank mates are small and non-aggressive. If the harlequin rasbora tank mates are aggressive then it would be a mess in the fish tank.

Characteristics of harlequin rasbora fish

The scientific name of Harlequin rasbora fish is Trigonostigma heteromorpha.

Harlequin rasbora is a fish breed having metallic colour and it is easy to maintain. Harlequin rasbora belongs to the Cyprinidae family. They are peaceful and are found in southeast Asia, Sumatra, Singapore and Thailand. They are omnivores and are egg-laying fishes. They can survive at a pH range of 6.0 to 7.5.

Among the species of rasbora, harlequin is the most popular species. They are also called red rasbora.

They are found in rivers and streams having a low mineral content and high concentration of humic acid. The humic acid is high in the water that swift through swamped forests. The waterlogged soil of forests decays leaf litter resulting in peat that leaches humic acids. This type of water is present in black water in South America.

Harlequin are freshwater fishes and not the brackish water. They are found in low water which is acidic in nature. They like subdued lighting and dense vegetation. They love to swim in open areas and are found in soft water.

Harlequin rasbora diet

They feed on a variety of diets like live food which primarily consists of insects, frozen dried food and flakes. These varied diet choices help them improve their digestion and are less prone to diseases. They also feed on worms like daphnia which are excellent supplemental food.

Worms are an excellent source of protein and it should be balanced with other supplements to keep your fish healthy and fit.

You need to make sure that the food is safe to use and offer the food in smaller chunks as the fish has a small mouth and cannot take large bites.

Harlequin rasbora tankmates are safe from the predatory behaviour of harlequin rasbora fish as long as the fish is not adult.

Difference between male and female rasbora

Female rasbora is larger than male and has a straight black wedge. Male are more slender than females and have a rounded extension at the bottom edge of the black wedge covering the posterior part of the male.

Harlequin rasbora size

Harlequin has a size of 2 inches which is when they are fully grown. This size is very rare. Most of them will have a size of 1.75 inches. They are small fishes and are excellent to be kept in small tanks.

Harlequin rasbora tank size

The minimum tank size for harlequin rasbora fish is 10 gallon. These fishes are schooling fishes, meaning you cannot keep a single fish in the tank, you need to have at least 10 of the fishes to make a school. 

You should have a pair of this fish in each gallon of water. For instances, if you have 10-gallon fish tank then the number of fishes would be 20 in this case. It is easy to care for these fish but it doesn’t mean that you simply toss this fish and forget it.

We would suggest you have a large aquarium in case you have the room and the budget despite the small size of the harlequin rasbora fish.

Harlequin rasbora tank mates should not be few in numbers. The larger the number of fishes the beautiful is the display of the aquarium.

You can have a tank size of 20 to 30 gallons which is enough for your fish to adjust and swim freely.

Water chemistry of the tank

The most important factor in fish survival and welfare is the type of water condition they are comfortable with. You should provide the same water condition over and over again in which the fish is comfortable and are not prone to environmental changes.

The water condition in which the harlequin rasbora fish is comfortable is like black water of southeast Asia.

The environment of harlequin rasbora fish in the wild is very different from most of the fishes. They live in water that is dark but not stinky and dirty. The dark colour of the water is due to decaying leaves and humic acid. They live in an environment that is slightly acidic in nature.

When you are setting up the environment of the tank you need to maintain the water condition as before instead of making it murky all the time.

The important factors in water chemistry are:

  • pH levels: 6.0 to 7.8 (6.5 is best)
  • Water temperature: 72°F to 80°F( 74 is the best)
  • Water hardness: 2 to 15 KH( low is best)

You need to maintain the water conditions by checking the water daily and testing it. By testing it you will know the change in water condition and its effect on the harlequin rasbora fish.

Harlequin rasbora fish mates need to be adjusted in the same water conditions as that of harlequin rasbora fish.

Maintaining the inside of the tank

Now let’s dive into the details of the inner environment of the fish tank.

The first thing you need to consider is the substrate. The substrate should be dark coloured sand or gravel. The fish do not spend much time in the bottom of the fish tank so you need not worry about the injury that is caused by the gravel.

Now introduce some plants in the fish tank. Harlequin rasbora fish love plants because these plants offer them protection when they are in danger. These plants include Cryptocoryne or species of the broad-leaved plants.

Cryptocoryne are the plants that are native to the area that belongs to harlequin rasbora fish so they love to swim between them. Their leaves are soft and silky when touched.

Diseases and prevention

They are very hardy and tough and are less prone to diseases and ailment. However, they get sick too like other fishes.

The most common disease is Ich. It can affect any freshwater fish and is mainly caused by poor water conditions. The poor water conditions lead to stress and when the body is stressed the immune system is depressed and the body is more prone to diseases.

You can prevent the diseases of freshwater fishes by constantly maintaining the inner environment of fish tanks and giving them proper diet and nutrition.

The behaviour of the harlequin rasbora fish

Harlequin rasbora fish are peaceful creatures and are not aggressive. They are small passive fishes and therefore they are an easy target for larger fishes. Harlequin rasbora tank mates should be small passive so that the environment of the tank remains peaceful.

The real strength of the harlequin rasbora fish is they move in large groups. They do things individually sometimes but most of the time they remain in groups.

Harlequin rasbora tank mates need to be adapted to the environment in which the harlequin rasbora fish is kept. The best harlequin rasbora tank mate is betta fish but as long as the tank has enough space to adjust betta fish.

Harlequin rasbora tank mates that are double the size of harlequin rasbora fish cannot live in the fish tank because they can eat them. One of the common examples of this fish is Cichlids.

Breeding of harlequin rasbora fish

It is not easy to breed the harlequin rasbora fish but it is not impossible. You need to provide the same environment to your fish as provided by the wild. You should give them a protein diet like blood worms are the best choice. A slight warm temperature would be good.

You need two females for one male. You also need broad leaves in the tank because the female encourages the male to mate by rubbing their bellies on the broad leaves. This signals the male to come and fertilize the egg. The egg attached to broad leaves hatches in 24 hours.

You need to separate the parents from the hatched one because they try to eat them. Newly hatched fry will feed on yolk for 24 hours and afterwards you need to feed him or her brine shrimp.

It would be better if harlequin rasbora tank mates are of the same species as the harlequin rasbora itself.

They are peaceful and the only thing that is difficult to maintain is the breeding of this fish but following the right methodology, it is not difficult to breed them in the tank.

They can be adjusted in any tank, especially in a Betta tank.


After reading this article on “Harlequin Rasbora tank mates” the reader will be able to take good care of this fish. He will also know about the breeding process and the diet that is necessary for this fish.

Feel free to ask anything about “Harlequin Rasbora tank mates” in the comment section below.

FAQ; Harlequin rasbora tank mates

Frequently asked questions of “Harlequin rasbora tank mates” are:

Are Harlequin Rasboras fin nippers?

No, harlequin rasbora are not fin nippers. They live in a school of fishes very peacefully.

Can Harlequin Rasboras live with guppies?

Yes, harlequin rasbora can live with guppies. Both of them are compatible with each other because both have a peaceful nature and you wouldn’t see any clash among them.

How long do Harlequin Rasboras live?

Harlequin rasbora live from 5 to 8 years in the captivity if provided good care and nutrition. They are less likely prone to illness and other conditions.

Why are my Harlequin Rasboras dying?

The most common cause of harlequin rasbora death is dirty water. You should have a filter in the aquarium that can process the whole water of the tank 3 times per hour. Dirty water can also spread diseases.

Do Harlequin Rasboras need a heater?

Yes, you need to maintain the temperature between 72 to 82 degrees Fahrenheit. Harlequin rasbora fish are tropical fishes and cannot live below 70 degrees Fahrenheit.

Do Harlequin Rasboras jump?

They are not natural jumpers. The jumping you are watching is because of many reasons. One of the reasons is the water is not suitable for them or they are being preyed on. Some of the fishes remain in the middle layer of the water and rarely come to the surface of the water.











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