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

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

This species is loved by aquarists because of their ease of care and stunning appearance. Watching a school of them swimming around just never gets old!

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

Species Summary

Harlequin Rasboras (Trigonostigma heteromorpha) are one of the most popular schooling fish in the world. Thanks to their shimmering color and iconic markings, they produce a beautiful show in aquariums of any size.

Sometimes called Red Rasboras, these freshwater fish are endemic to Southeast Asia. They can be found in Thailand, Malaysia, Sumatra, and Singapore. Usually, they habitat fresh blackwater streams and ponds.

Since they were discovered over 100 years ago, Harlequin Rasboras have been a hot commodity in the fish-keeping community. Thanks to their stunning appearance and hardiness, they’re a great fish for aquarists of any skill level.

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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.


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.

The side profile and colors of a Harlequin Rasbora

The fish have a distinct light pink or orange 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. Typically, the patch is slightly 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. Unlike other fish species, the females are the dominant-looking ones. They’re larger and girthier than the males.

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).


Harlequin Rasbora 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.

A lone Harlequin Rasbora swimming in an aquarium

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.

Tank Size

The minimum tank size for Harlequin Rasboras is 10 gallons. 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 the space in your home and budget.

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

Author Note: We find that giving these fish a little extra room brings out their active side a bit more. This makes for a better viewing experience if you’re someone who likes to spend a lot of time watching their tank!

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 to 15 KH (the lower 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.

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.

The Cryptocoryne plants are native to the same region that Harlequin Rasboras are from. Not only that, but they’re soft and leafy enough to swim through.

Author Note: Add plants sparingly. You want to have plenty of vegetation in the tank without overcrowding it. Leave a good amount of open space in the center of the tank for schooling and swimming.

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.

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 its 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.

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. To keep your fish happy, you need to keep the tank peaceful with smaller passive species.

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

A school of Harlequin Rasboras

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 part of the aquarium.

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.

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:

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!

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.


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 give it that added boost of comfort, throw in some peat moss. This will incorporate those humic acids found in blackwater environments.

Make sure that there are some broad-leaf plants in the tank. The females will use the leaves to keep the eggs protected.

When you’re ready, introduce a group of Harlequin Rasboras. 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 a good option.

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. After about 24 hours, the baby fish will emerge from their eggs. 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.

Now You’re Ready

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!

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