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

Harlequin Rasboras are an eye-catching species of freshwater fish that provide a bright splash of color to aquariums all over the globe.

Adored by aquarists, these fish are easy to care for and make for an impressive visual display. No matter how often you see a school of them swim around, it never gets old!

This guide provides all the information you need to know to care for Harlequin Rasboras. We’ll cover tank mates, size, habitat, breeding, lifespan, and more!

Whether you’re a seasoned aquarist or just starting, this guide will provide all the knowledge you need to keep your Harlequin Rasboras thriving and satisfied in their new home.

Species Summary

Harlequin Rasboras, or Red Rasboras, have become a favorite among aquarists due to their vibrant colors and markings. They create a stunning display in any aquarium, regardless of its size.

These fish, native to Southeast Asia, can be found in Thailand, Malaysia, Sumatra, and Singapore, where they inhabit fresh blackwater streams and ponds.

These fish have been a popular choice among hobbyists for over a century. Moreover, they are incredibly hardy and easy to care for, making them a great addition to any aquarium.

With their captivating color and iconic patterns, these fish are one of the world’s most beloved schooling fish.

They add incredible beauty and vibrancy to any aquarium, making them a must-have for any fish lover.

Average Harlequin Rasbora Size

The Harlequin Rasbora reaches a maximum size of around 2 inches when kept in an aquarium. These fish grow very little, mostly around the 1.75-inch, and this makes them an ideal choice for tanks that are on the smaller side.

Considering the size, these fish can uniquely appeal to your aquarium. They will only take up a little space and can be a great addition if you want something special.


If you want your Diamond-like Southeast Asian fish to live a long and happy life, it’s important to know that Harlequin Rasboras have a 5-8 years lifespan.

Most of these fish have lifespans of around 6 years, with certain factors deciding if they can make it to the upper limit of that number. This species in freshwater is unique because its survival is greatly affected by the quality of its habitat and water.

You can ensure your little friends thrive and enjoy a healthy existence with proper care and attention.


The Harlequin Rasbora stands out with its diamond-like shape. It’s thicker in the middle and thins towards the head and tail, and the tail is particularly tapered, emphasizing its unique silhouette.

These fish display a variety of pink and orange color tones, with variations between individuals and the potential to shift with the water conditions. The color is most noticeable on the upper body and gradually fades to white on the underside.

Some fins may also take on a richer shade than the rest of the body. The pelvic and anal fins, however, are usually transparent.

The name “Harlequin Rasbora” comes from the bold black patch on their bodies. Each fish has a wedge-shaped marking that resembles traditional jester costumes, and it starts at the dorsal fin and ends at the base of the tail. The rest of the body is unadorned, making the pattern even more striking.

Males and females have slight differences in their markings. The patch is usually bigger on males, and the bottom of the triangle may be rounded.

Harlequin Rasbora Care


Harlequin Rasbora care is surprisingly straightforward, even for those just starting fish-keeping. These fish are quite hardy and can handle changes in temperature with ease.

But that doesn’t mean you can just plop them into any tank! These fish need the right environment to thrive, like any other species.

Follow the guidelines below to give your fish the best chance at a healthy life.

Tank Size

You’ll need to ensure your tank is at least 10 gallons to give your diamond-shaped Harlequin Rasboras plenty of room to swim comfortably. Choosing the right tank size for your fish is important, as overcrowding can cause stress and health problems.

While a smaller tank may seem more manageable, it can lead to a buildup of toxins and waste that can harm your fish. On the other hand, a larger tank can provide more room for your fish to explore and can be easier to maintain with proper filtration.

When choosing the right tank, consider the pros and cons of different tank sizes and the needs of your Harlequin Rasboras.

Optimal filtration is also important to maintain good water quality and keep your fish healthy. A filter that can handle 2-3 times the volume of your tank is recommended, and regular water changes are essential to keep the water clean.

Your Harlequin Rasboras can thrive in their new home with the right tank size and filtration.

Water Parameters

The right water conditions can help your fish thrive and stay healthy, while poor water quality can lead to stress, disease, and even death. Maintaining pH, temperature, and filtration is crucial for the well-being of your Harlequin Rasboras.

Here are some key points to keep in mind when it comes to water parameters:

  • Regularly test your tank water to ensure it meets the right pH, ammonia, nitrite, and nitrate levels.
  • Use buffers or other chemicals to adjust your water’s pH and hardness if necessary.
  • Harlequin Rasboras prefer a temperature range of 72-80°F, so use a reliable heater to maintain a stable temperature.
  • A good filtration system helps to keep the water clean and clear and removes harmful substances like ammonia and nitrite.
  • Proper water parameters are essential for the health and well-being of your fish and can help them live longer and happier lives.
  • When considering the pH levels for your aquarium, the ideal range is 6.0 to 7.8, with the sweet spot being 6.5.
  • Water hardness, the lower, the better, so aim for numbers between 2 and 15 KH.

By following these guidelines, you can create a healthy and happy home for your Harlequin Rasboras that will allow them to thrive and flourish.

Setting Up Their Tank

Let’s start setting up your aquarium for these beautiful Harlequin Rasboras! Since they prefer warm blackwaters with a slightly acidic pH balance and low mineral content, choosing the right filtration system and decor options for your tank is important.

Live plants like Cryptocoryne are recommended for tank decor, but you can also use driftwood and rocks to create a natural-looking environment. Make sure to avoid any sharp or rough edges that could harm your fish.

Additionally, consider adding a dimmer switch to your lighting system, as Harlequin Rasboras prefer low light levels and can be easily stressed by bright lights.

When it comes to filtration systems, you have a few options. A sponge filter is a good choice, as it will only create a little current and provide a gentle water flow. A hang-on-back filter can also work well, but keep it on a low setting to prevent too much agitation in the water.

Whichever filtration system you choose, cycle your tank properly before adding any fish, and this will ensure that the water is healthy and free from harmful toxins.

With the right decor, filtration system, and lighting requirements, your Harlequin Rasboras will thrive in their new home!

Potential Diseases

Knowing about potential diseases that could affect your Harlequin Rasboras and how to prevent them is important.

Poor water conditions can cause Ich, a common freshwater disease that manifests as white spots on the fish’s body. Maintaining a clean tank and monitoring water parameters regularly is essential to prevent this disease.

Suppose you notice any symptoms of Ich, such as white spots or lethargy. In that case, you should immediately isolate the affected fish and treat the tank with medication to eradicate the parasite.

Another disease that can affect your Harlequin Rasboras is Fin Rot, which is characterized by the deterioration of the fins. This disease can be caused by poor water quality or bacterial infections and can lead to the loss of fins if left untreated.

Preventative measures for Fin Rot include regular water changes and maintaining a healthy environment for your fish. If you notice any signs of Fin Rot, such as ragged or frayed fins, you should isolate the affected fish and treat the tank with antibacterial medication.

Early detection and treatment are crucial for preventing this disease’s spread and ensuring your Harlequin Rasboras’s health.

Food & Diet

These little guys are not picky and will happily munch on various foods. Feeding options include bloodworms, Daphnia, or brine shrimp, which provide a good dose of protein. Just ensure the food is safe and small enough for their tiny mouths.

Nutritional balance is important, too, so try to provide a variety of foods to ensure your Harlequin Rasboras get all the nutrients they need.

When it comes to feeding Harlequin Rasboras, it’s important to remember that they are opportunistic eaters and will eat pretty much anything they can. However, you should still be discerning in your food choices to ensure their health and well-being.

Safe food choices include live or frozen foods free from parasites and bacteria. Additionally, provide a variety of foods to keep your Harlequin Rasboras happy and healthy.

With the right diet, these little fish will thrive in your aquarium!

Behavior & Temperament


These little fish are a joy to watch as they swim peacefully in their warm, slightly acidic blackwater tank with their fellow schooling companions.

Harlequin Rasboras are known for their schooling behavior, an instinct for survival in the wild. In a group, they feel safer and more confident exploring their surroundings. They swim together in harmony, creating a beautiful display of synchronized movements.

Regarding compatibility with other fish, Harlequin Rasboras are generally peaceful and non-aggressive. They prefer the company of their kind and should be kept in groups of 8-10 individuals.

They also get along with other small and peaceful fish like tetras, gouramis, and corydoras. However, it’s important to note that they are incompatible with aggressive or fin-nipping fish like bettas or barbs.

Tank Mates

When considering tank mates for your Harlequin Rasboras, remember that they are schooling fish and prefer to be in groups of 8-10 individuals. You can pair them with other small, peaceful species like tetras, gouramis, and corydoras.

These fish will get along well with Harlequin Rasboras and add variety and color to your aquarium.

Just be sure to avoid aggressive or fin-nipping fish like bettas or barbs, as they may harm your Harlequin Rasboras. These fish are great for creating a peaceful and vibrant community aquarium.


You should know a few things if you’re interested in breeding these little beauties. First, you’ll need a separate breeding tank with appropriate water conditions and live food.

Harlequin Rasboras prefer slightly acidic water with low mineral content, so keep the pH around 6.0-6.5 and the water temperature between 75-80°F. For live food, you can try infusoria or baby brine shrimp.

Once you set up the breeding tank, you must introduce a pair or group of Harlequin Rasboras and wait for them to spawn. Breeding requirements for Harlequin Rasboras are relatively simple, females will lay their eggs under broad-leaf plants, and males will fertilize them.

After breeding, adult fish should be removed from the breeding tank to prevent them from eating the fry. Baby fish will emerge after 24 hours and should be fed fine infusoria for the first two weeks before transitioning to powdered fish food. It takes about 6 months for Harlequin Rasboras to reach full maturity.

You can successfully breed these beautiful fish in your home aquarium with proper breeding tank setup and fry care.


Congratulations! You now have all the information you need to take care of your Harlequin Rasboras. Remember to keep their tank clean and well-maintained and to provide them with a balanced diet.

These fish are peaceful and social, so ensure they have plenty of space and compatible tank mates.

If you’re interested in breeding your Harlequin Rasboras, set up a separate breeding tank and provide them with the right conditions.

With their striking coloration and active personalities, Harlequin Rasboras will surely be a great addition to any aquarium. Happy fish keeping!