Skip to Content

Harlequin Rasboras: Complete Care Guide (Diet, Tank & More)

get 5 secrets to thriving plants

Harlequin rasboras are beautiful little fish that go great in a larger tank. They have a pleasant demeanor and are easy to care for.

Keep reading to learn how to care for a vibrant school of harlequin rasboras and to ensure they thrive in your freshwater tank.

Harlequin Rasbora Care Guide

Common Name:Red rasbora, Harlequin rasbora, harlequin fish, harlequin tetra
Scientific Name:Trigonostigma heteromorpha
Adult Size:1.75 Inches
Minimum Tank Size:10 Gallons or More 

Harlequin rasboras are small reddish-copper fish that are common with new freshwater aquarium hobbyists. They are easy to care for and add a beautiful metallic coloring to your tank. They do best in schools of 8 to 10 fish of their kind.

Trigonostigma heteromorpha Harlequin rasbora

Harlequin Rasbora Size, Lifespan & Appearance


Harlequin rasboras are on the smaller side of the spectrum of most freshwater aquarium fish.

For this reason, they are very popular with freshwater aquarium owners. They also have a pleasant demeanor and do well amongst a group of their kind.

With that being said, harlequin rasboras grow to around 1.75 inches to 2 inches. The females are a bit larger than the males which is common amongst fish.

Colors and Markings

Harlequin rasboras have a diamond-shaped body that is a mixture of orange and pink in color.

They often appear to be copper in color due to the mixture of these colors. They also have a black wedge-shaped marking on the lower half of their body. 

An interesting fact about the harlequin rasbora is how they got their name in the first place!

The name harlequin comes from a joker’s costume (on a deck of cards) because of the coloration similarities. 

Gender Differences

Despite the males and females having the same colorations, there are a few differences between the two.

Female harlequin rasboras are larger and a bit thicker than their male counterparts.

A good differentiator between the two is that the males have a dorsal patch that goes straight from the head to the end of the fish. It also becomes round at the end. The females do not have these distinguishing features on their dorsal patches. 


The lifespan of a harlequin rasbora is dependent on its environment. In the wild, they only typically live about 3 years. However, they can live between 5 to 8 years in a freshwater aquarium. 

Of course, this is dependent on their genetics, and if their tank is kept clean and within the correct parameters at all times. 

Feeding Harlequin Rasboras: Food & Diet 

Harlequin rasboras are omnivores that will need various foods to stay healthy.

Your harlequin must have a well-balanced diet consisting of high-quality pellets and flakes, as well as the occasional live food such as brine shrimp, or bloodworms.

It is best to always make sure that the food given to the harlequin is safe for them to consume.

Since they have such small mouths, they aren’t always able to consume common fish foods. Keeping the food tiny is best to ensure that the harlequin rasboras can safely swallow.

You should also be feeding your harlequin rasbora smaller amounts of food several times a day.

This is opposed to feeding your fish a large amount of food once a day, which is common for some fish.

Keep in mind you should only give them what they can consume within two to three minutes to avoid any digestive issues in your school of fish.

However, if you do choose to only feed once a day, increase the timing to about five minutes, and again only give them the amount that they can consume in this five minutes.

It is also a good idea to remove any uneaten excess food from the bottom of your tank to keep your tank clean and avoid changes in your tank’s water parameters.

Harlequin Rasbora Tank Mates

As mentioned, the harlequin rasbora is a schooling fish that should be kept in larger groups.

Rasboras prefer to be in a group of at least 8-10 fish. Make sure you have enough of the harlequin rasboras before looking into adding different types of fish to your tank.

It is also very important to ensure that there is plenty of extra room in your tank for them to swim and roam around. You do not want to have just enough room for them to swim to a few spots. 

With that being said, there are quite a few different fish that are peaceful and compatible tank mates for the harlequin rasbora if there is enough room for them.

These tank mates are small and non-aggressive like the harlequin.

  • Mollies
  • Guppies
  • Neon tetras
  • Platies
  • Cory Catfish
  • Other small rasboras 

Tank Mates to Avoid

You will want to avoid adding fish to your tank if they are larger than twice the size of your harlequin rasboras.

Aggressive or territorial breeds should be avoided as well. This is because your harlequin rasboras will get attacked and become prey.

A few examples of aggressive or larger fish to avoid adding to your tank are angelfish, cichlids, Oscars, and jack dempseys.

Ideal Tank Set-Up

Tank Size

Since the harlequin rasbora is a smaller fish, it does not need a ton of room in your tank.

However, they are schooling fish and need to be in a larger group of 8-10 of their own kind. You can keep a pair for every gallon of water in the tank. 

A tank size of 10 gallons is the minimum for a decent group of harlequin rasbora.

However, using a larger tank, 20 to 30 gallons, gives your school of harlequin rasboras more room to swim and be active.

Blackwater Environment

When setting up a tank you’ll want to keep the harlequin rasbora’s natural habitat in mind.

This means replicating a blackwater environment inside your tank. Therefore, they need warm slightly acidic soft waters to live and thrive in. These water parameters will be covered in the next section. 

You’ll also want to set a good filtration system for the tank that does not make a strong current in the water.

The harlequin rasboras are used to very slow-moving water in the wild and having a high-powered filter may be stressful for them.

It is also recommended to use a dark substrate at the bottom of your tank. This not only copies that of their natural habitat but will also encourage them to present their brightest colors.

Add Plants

Adding live plants into your tank is crucial for the harlequin rasbora. They originate from highly dense vegetation waters. They use their live plants to swim through, hide, sleep, and also to breed. 

Putting floating plants and leaves at the top of your tank will create a dim lighting environment which is what they are used to in the wild.

The shadows that the plants create darken the water, and this can also give them an extra sense of safety.  

There are certain plants that you should stay away from such as Caladium or Daphne, as they are not good for them, and some are toxic to the harlequin rasbora, so it is best to research the plants before adding them to your harlequin tank. 

Desired Aquarium Water Parameters

Since the harlequin rasbora originates from the dark waters of blackwater streams and ponds, it is best to maintain the following water parameters to ensure a healthy environment for them.

  • Water Temperature: Between 72°F to 80°F; a temperature of 74°F is most ideal and what you should aim for
  • pH Levels: Between 6.0 to 7.8 is recommended; however a 6.5 is most ideal 
  • Water Hardness: Between 2-5 KH; the lower your water hardness, the better

Fortunately, the harlequin rasboras are typically hardier than other fish. This means that the water parameters can change slightly without harm to the fish.

However, they should be kept at the same levels if possible.

The parameters can unexpectedly change due to an increase in waste in tanks, dead fish, or decomposing plants. 

How to Breed Harlequin Rasboras

The harlequin rasbora is one of the more difficult kinds of fish to breed. They require ideal conditions that are crucial to follow, and it is best to mimic their natural habitat as much as possible.

With that being said, if these pointers are followed, you shouldn’t have too much of a problem. 

Before breeding it is best to select a younger fish and give them a proper diet, or nutrient-rich foods (such as live food) several times a day.

This will help prepare for breeding as the females fill up with eggs. Conditioning the fish will also bring out the male’s color to a more vibrant tone.

Breeding Tank Conditions

As previously mentioned, the harlequin rasbora needs to have certain conditions to try to breed, so it is very important to set up your breeding tank to the requirements that will replicate their natural habitat.

To set up the breeding tank, you will want to start off with having dim lighting which replicates the low light of the water they come from.

Keep the water shallow in your breeding tank, about six to eight inches in height.

Make sure the water parameters are ideal for what the harlequin rasbora needs in order to breed if this is different from the water parameters of their main tank.

It is important to adjust the parameters slowly so as to not stress the fish out or put them in shock.

Ideally, your water temperature should be around 77 — 82.4°F, but ideally closer to  80°F. The water should be very soft, as they are used to barely any mineral content in nature.

You will want a water hardness no greater than 2.5 dGH. In nature they live in more acidic waters, so you will want a pH level of about 6.5.

Keep in mind that they are used to blackwater environments full of vegetation, so you will want to add broad-leaf plants to the breeding tank.

The female will lay her eggs under the leaves of the plant, which are also used for the protection of the eggs.

Common broadleaf plants you can use in your aquarium include the cryptocoryne or microsorum.

Breeding Process

When selecting your fish to breed it is best to have two males for every female fish. The male will initiate the breeding process in the early morning, by attracting the female to an ideal mating spot.

Once the female is ready, they will go under the leaves of the plants that you added into the tank. 

The female will lay about 6-12 eggs at a time. The male will then fertilize the eggs. The fertilized eggs will stick to the underside of the leaves. The female will normally lay around 80-100 eggs within an hour or two.

As soon as they are done spawning and laying eggs, immediately remove the parents and put them back in their original tank. Harlequin rasboras will eat their eggs after spawning, as well as the fry.

After removing the parents from the breeding tank, it will take about 18 hours for the eggs to hatch. They will then become free swimming in approximately three to five days. 

During the first few days feed the fry infusoria. They do grow quickly and can start eating baby brine shrimp when they are about 7-14 days old. 

Origin & Natural Habitat

Originating in tropical waters in Southeast Asia, the harlequin rasbora can be found throughout Singapore, southern Thailand, and western Malaysia.  They inhabit the heavily vegetated swamps and forest streams. 

The harlequin rasbora’s natural habitat is full of floating plants and leafy vegetation. This is what creates the dark water environment.

As the plants filter through sunlight it creates pleasant dim lighted waters that the harlequin rasbora feels safe in. The water is slow-moving with high concentrations of humic acid, and low mineral content.

get 5 secrets to thriving plants