Harlequin Rasbora – Care, Feeding, Tank Mates & Full Details!

Harlequin Rasbora, bearing the scientific name Trigonostigma heteromorpha, are stunning freshwater fish gracing aquariums worldwide. Recognized for their beauty and ease of care, they are a favorite among novice and experienced aquarists alike.

Harlequin Rasboras are undoubtedly a delightful spectacle in freshwater aquariums, offering an engaging visual experience with their vibrant colors and dynamic behavior.

Also referred to as Red Rasboras, Harlequin Rasboras are indigenous to Southeast Asia, inhabiting fresh blackwater streams and ponds in Thailand, Malaysia, Sumatra, and Singapore.

The allure of these freshwater gems, discovered over a century ago, is their radiant coloration and distinctive markings, making them an aesthetic delight in aquariums of any size.

Their resilience and captivating beauty make them an ideal choice for aquarists, irrespective of their expertise level.

Our comprehensive guide will delve into every facet of Harlequin Rasbora care – from understanding their unique appearance, determining appropriate tank mates, to the art of successful breeding.

Recently Harlequin Rasbora species has become very popular and can be found in many pet stores. The fish themselves are unpretentious, and it is interesting to watch them since they behave quite actively in the water.

Quick Stats About Harlequin Rasbora

Scientific name: Trigonostigma heteromorpha
Common names Red rasbora, harlequin fish, harlequin rasbora, harlequin
Distribution: Singapore, Malaysia, Sumatra, and southern Thailand
Size: 1.75–2 inches
Life expectancy: 5–8 years
Color: Orange-pink body with a black wedge-shaped marking
Diet: Omnivore
Temperament: Peaceful
Minimum tank size: 10 gallons
Temperature: 72–81°F (22–27°C)
pH: 6.0–7.8
Hardness: 2–15 dGH
Care level: Easy
Breeding: Egg-layer

Appearance of Harlequin Rasbora

Often referred to as a living gem, the Harlequin Rasbora’s appearance is truly remarkable and mesmerizing.

Boasting a unique diamond-like shape, they are known for their more rounded bodies in the center, with the head and tail tapering into finer points. This distinctive shape accentuates their vibrant color palette.

One cannot ignore the alluring pinkish-orange hue that pervades their bodies. The color intensity may vary from fish to fish and may be influenced by water conditions.

This coloration envelops their heads and bodies, with the most intense color concentration usually observed on the top of their bodies.

In contrast, their bellies often exhibit a lighter, almost white tone.

The Harlequin Rasbora’s fins do not escape this color spectacle. The dorsal and caudal fins often display a richer hue than the body, creating a captivating contrast with their body’s more muted tones.

On the other hand, the pelvic and anal fins are frequently transparent, adding another dimension to their visual appeal.

The defining characteristic of these fish, however, is the striking black patch on their bodies.

This wedge-shaped marking starts at the dorsal fin and tapers to a fine point at the base of the tail. This pattern, evocative of traditional jester costumes, earns these fish their “Harlequin” moniker.

Natural Habitat of Harlequin Rasbora

The natural habitat of the Harlequin Rasbora encapsulates the warm, tropical blackwater environments of Southeast Asia.

These waters are dark due to high concentrations of humic acid from decaying plant matter, providing a unique setting for these fish.

These waters may appear murky due to high tannin content, but they are typically clear and contain low mineral content, giving them a slightly acidic pH balance.

Replicating these conditions in your aquarium will help your Harlequin Rasboras feel right at home and display their best colors and behaviors.

Origin and Distribution Of Harlequin Rasbora

Tracing their origin and distribution, Harlequin Rasboras (scientifically named Trigonostigma heteromorpha) are native to Southeast Asia. Specifically, they hail from Thailand, Malaysia, Sumatra, and Singapore.

These locations offer ideal conditions for these freshwater fish, with blackwater streams and ponds providing a perfect setting for their survival and growth.

Ever since their discovery over a century ago, Harlequin Rasboras have held a firm place in the hearts of aquarists around the globe.

Their dazzling appearance and hardiness make them an ideal choice for fish enthusiasts, regardless of their skill level.

Growth, Size & Lifespan of Harlequin Rasbora

The growth, size, and lifespan of the Harlequin Rasbora reflect its hardy nature and suitability for home aquariums. Typically, the Harlequin Rasbora will grow to about 2 inches in length when in captivity, although most individuals will likely reach around 1.75 inches.

Despite their small size, these fish have a significantly long lifespan compared to other freshwater species.

They can live between 5 and 8 years, with proper care and suitable genetic factors often enabling them to reach the higher end of that range.

This impressive lifespan is influenced significantly by water conditions and habitat quality, underlining the importance of proper tank maintenance and care for these captivating creatures.

Harlequin Rasboras Behavior and Temperament

The Harlequin Rasbora’s behavior and temperament reveal a peaceful and social species. They are naturally schooling fish, preferring to swim in groups of at least 5-6 individuals.

This social nature enables them to showcase their vibrant group dynamics, and you will often see them darting around the tank in an energetic yet synchronized ballet.

Harlequin Rasboras are also quite shy. When they’re in a group, this shyness dissipates, giving way to more confident and playful behavior.

However, when alone, they tend to hide, underlining the importance of keeping them in adequate numbers.

Overall, their behavior and temperament make them an excellent addition to community aquariums.

Tank Setup for Harlequin Rasbora

Setting up the perfect environment for Harlequin Rasboras goes beyond the basics.

Here’s a deep dive into the essential components of their ideal tank setup:

Tank Size

A tank size of at least 10 gallons is recommended for a small group of Harlequin Rasboras. However, a larger tank of around 20-30 gallons would allow for a bigger school and provide them with more swimming space, contributing to their overall well-being.


The substrate should ideally be dark to mimic the Rasbora’s natural blackwater habitats. Using dark, smooth gravel or sand can help replicate these conditions, encouraging natural behavior and enhancing their coloration.

Decorations and Hiding Spots

When considering decorations and hiding spots, think natural. Incorporate live plants, driftwood, and rock formations to offer security and mimic their natural habitat. Plants like Java Fern or Anubias are great options.

Water Parameters

Water parameters are crucial for the Harlequin Rasbora’s health. Maintain a pH level between 6.0-7.5, a temperature range of 72-81°F (22-27°C), and a water hardness of 2-10 dH.

Filtration and Aeration

For filtration and aeration, use a high-quality aquarium filter to ensure clean, oxygen-rich water. Air pumps can supplement aeration, though they aren’t essential if your filter creates enough surface agitation.


When it comes to lighting, moderate levels are best to mimic the slightly dim environments of their natural habitats. However, it should be balanced with the needs of live plants if you have them in your aquarium.

Tank Mates

Choosing the right tank mates is crucial. Other peaceful species like Tetras, Guppies, or Corydoras Catfish are ideal. Avoid aggressive or large predatory fish that can cause stress or harm to the Rasboras.


The Harlequin Rasbora is omnivorous and will enjoy a balanced diet. Feeding them high-quality flake food, brine shrimp, and daphnia will keep them healthy and vibrant.

Remember, a varied diet is key to their well-being.

However, caring for a Harlequin Rasbora isn’t just about the initial setup; ongoing maintenance is a must.

Let’s delve into the crucial aspects of tank maintenance, including regular water changes, cleaning practices, filter upkeep, and how to monitor the health of your Rasboras.

Tank Maintenance of Harlequin Rasbora

An optimal tank environment is central to your Harlequin Rasboras’ well-being.

Regular cleaning, diligent water changes, filter upkeep, and close monitoring of your fish’s health contribute to a thriving aquatic community.

Water Changes

Regular water changes are vital in a Harlequin Rasbora tank. These changes help control nitrate levels and remove any harmful waste or chemicals.

Aim for a 25-30% water change every week. Always ensure the new water matches the temperature and pH of the existing tank water to avoid shocking the fish.

Cleaning the Tank and Decorations

Cleaning the tank and decorations might seem daunting, but it’s essential for your Rasboras’ health. Algae can build up on tank walls and decorations over time.

Use an aquarium-safe scraper or brush to gently remove this algae during water changes. Be careful not to disturb the tank’s substrate, as this could disrupt beneficial bacteria essential for a healthy aquarium ecosystem.

Filter Maintenance

Filter maintenance is a critical yet often overlooked aspect of tank upkeep. The filter removes harmful toxins, keeps water clear, and aids in oxygenating your tank.

Rinse filter media with tank water (never tap water, as it could kill beneficial bacteria) during water changes.

Replace media as per manufacturer guidelines, and check the filter regularly to ensure it’s working effectively.

Monitor Fish Health

Last but not least, always monitor your fish’s health. Healthy Harlequin Rasboras are active with vibrant colors. Watch out for any signs of disease or stress such as loss of color, lethargy, erratic swimming, or loss of appetite.

Regular observation will help you spot any potential problems early, enabling you to take swift action to protect your aquatic pets’ health.

By adhering to these tank maintenance practices, you’ll ensure your Harlequin Rasboras live in an environment that encourages their natural behavior, promotes health, and showcases their exquisite colors.

Remember, a clean and well-maintained tank is key to a happy, thriving school of Harlequin Rasboras.

Acclimating Harlequin Rasbora

To make your Harlequin Rasbora feel right at home in their new tank, acclimation is essential. This procedure will allow them to adjust to the water conditions in their new environment gradually, reducing the risk of shock or stress.

Start by floating the bag containing the fish in the tank for about 15-20 minutes. This will equalize the temperatures.

Next, slowly add small amounts of tank water into the bag over the next hour, allowing your fish to adapt to the new water chemistry gradually. After this, gently release the fish into the tank.

Harlequin Rasbora Diet and Feeding

Harlequin Rasboras are omnivorous, enjoying a varied diet that includes both plant and animal matter.

Feeding your Rasboras a balanced diet will ensure they maintain their beautiful coloration and remain healthy and active.

Here are some key points to consider:

Flake and Pellet Foods

Offer your Rasboras high-quality flake or pellet foods daily. These foods are specially formulated to provide a balanced diet and are easy to consume due to the small size of Harlequin Rasboras.

Live and Frozen Foods

Supplement the diet of your Harlequin Rasboras with live and frozen foods. These could include daphnia, brine shrimp, bloodworms, or mosquito larvae. These foods add variety and are particularly useful for encouraging healthy breeding behavior.

Vegetable Matter

Consider adding some vegetable matter to their diet. Finely chopped spinach or peas can provide essential nutrients that your fish might not get from other food sources.

Feeding Times and Quantities

Harlequin Rasboras should be fed small amounts 1-2 times a day. Only provide what they can consume in a few minutes to prevent leftover food from decaying in the tank and causing water quality issues.

Harlequin Rasbora Tank Mates

Harlequin Rasboras are peaceful, schooling fish that get along well with other similarly sized, non-aggressive fish.

Here are some of the best choices:

  1. Neon Tetra: These fish are similarly sized and share the Rasbora’s peaceful temperament, making them ideal tank mates.

  2. Guppies: Known for their vibrant colors, guppies are peaceful and can coexist with Harlequin Rasboras.

  3. Dwarf Gouramis: Dwarf Gouramis are calm, slow-moving fish that won’t disrupt the Rasboras.

  4. Corydoras Catfish: These bottom-dwelling fish won’t compete for space and share a similar peaceful nature.

  5. Cherry Shrimps: These invertebrates are safe to house with Harlequin Rasboras, offering a bonus of additional color.

  6. Zebra Danios: Their active nature and similar size make Zebra Danios good companions for Rasboras.

  7. Platies: Platies are peaceful, easy to care for, and make a colorful addition to a Rasbora tank.

Tank mates to avoid for Harlequin’s:

However, some fish species should be avoided due to their aggressive behavior or size:

  1. Cichlids: Most Cichlid species are aggressive and can stress or harm your Rasboras.

  2. Oscars: These fish are larger and more aggressive, making them unsuitable.

  3. Bettas: Male Bettas can be territorial and aggressive.

  4. Arowana Fish: Their size and predatory nature make them a threat to your Rasboras.

  5. Piranhas: Despite being a freshwater species, their aggressive and predatory nature makes them unsuitable.

Breeding Harlequin Rasbora and Fry Care

Breeding Harlequin Rasboras can be a delightful experience.

Here’s a detailed guide on how to breed them and take care of the fry:

Preparing for Breeding

Prepare a separate breeding tank with slightly acidic water and a temperature around 80°F. Use broad-leafed plants for the female to lay eggs.

Identifying Sexes

Males are smaller and slimmer with a more curved black patch, while females are rounder with a straighter black patch.


The male will display a unique dance to woo the female. If the female is receptive, she’ll lay eggs on the underside of a leaf, which the male will then fertilize.


After spawning, remove the adults to prevent them from eating the eggs. The eggs will hatch in about 24-36 hours.

Caring for the Fry

Initially, the fry can be fed infusoria, moving on to brine shrimp nauplii as they grow. Keep the tank clean and monitor the fry’s health closely.

Signs of Stress in Harlequin Rasbora

Stress can be harmful to your Harlequin Rasbora, affecting their health and even their lifespan.

Here are a few signs to watch for:

  1. Abnormal Swimming: Harlequin Rasboras typically swim peacefully. If you notice erratic swimming or an increase in restlessness, it may signal stress.

  2. Loss of Appetite: A stressed Harlequin Rasbora may lose its appetite. Regular feeding routines and a balanced diet can keep this stress at bay.

  3. Fading Colors: If the vibrant colors of your Harlequin Rasbora begin to dull or fade, it could be due to stress.

  4. Breathing Heavily: Look for unusual breathing patterns, which might indicate anxiety or stress.

Common Health Issues and Treatments for Harlequin Rasbora

While Harlequin Rasboras are hardy fish, they can still suffer from common health issues:

  1. Ichthyophthirius (Ich): This is a common parasitic disease in aquarium fish. Symptoms include white spots on the body and gills. Treating Ich involves raising the water temperature and using aquarium salt or medication.

  2. Fin Rot: A bacterial disease that causes the fins to fray, discolor, and rot away. Clean water, reduced stress, and appropriate medication can prevent and treat fin rot.

  3. Fungal Infections: These manifest as fluffy, white growths on the body. Anti-fungal medications can help in these situations.

Regular water changes and monitoring water parameters can help prevent these issues and keep your fish healthy.

Additional Tips for a Healthy Aquarium

Maintaining a healthy aquarium is vital to the health and happiness of your Harlequin Rasboras:

  1. Water Quality: Ensure regular water changes and keep your filtration system clean.

  2. Diet: A balanced diet is essential. Consider a mix of high-quality flake foods and occasional live or frozen treats.

  3. Stress-Free Environment: Keep the tank free from aggressive species and create plenty of hiding spots.

  4. Regular Monitoring: Regularly observe your fish for signs of stress or disease.

Should You Get a Harlequin Rasbora for Your Aquarium?

Harlequin Rasboras can be fantastic additions to your aquarium. They bring vibrant colors, peaceful temperament, and are relatively easy to care for, making them suitable for beginners and experienced hobbyists alike.

Remember, they thrive in a community environment, so consider keeping a school of them together.

Keep in mind, they require a well-maintained and stress-free environment to thrive. If you can provide this, Harlequin Rasboras will prove to be a delightful addition to your aquatic family.

Conservation Status

Harlequin Rasboras are not currently listed as endangered or threatened according to the International Union for Conservation of Nature (IUCN). Their population in the wild is considered stable.

They are widespread throughout Southeast Asia, particularly in Malaysia, Singapore, and Thailand.

Despite this, it’s always important to purchase your fish from reputable breeders or stores. This ensures the preservation of their natural habitats and supports ethical breeding practices.

Availability & Pricing

Thanks to their popularity among aquarists, Harlequin Rasboras are widely available both in physical pet stores and online.

They are generally affordable, with prices varying depending on factors like age, size, and the seller’s location.

As of now, individual Harlequin Rasboras are often priced around $2-$4, making them a reasonably priced choice for those wanting to keep a school of vibrant, active fish.

However, prices may vary, so it’s always wise to check with your local stores or trusted online sellers.

Frequently Asked Questions About Harlequin Rasbora

In this section, let’s tackle some of the most commonly asked questions about Harlequin Rasboras.

1. How many Harlequin Rasboras should I keep together?

Harlequin Rasboras are schooling fish, which means they prefer to be in groups. Ideally, you should keep a group of at least five to six fish, although they will be happier in larger groups.

2. How long do Harlequin Rasboras live?

With good care and a healthy environment, Harlequin Rasboras can live for around five to eight years.

3. Can Harlequin Rasboras live with bettas?

Yes, they can! Harlequin Rasboras are peaceful fish that can coexist with bettas. They are neither aggressive nor fin nippers, making them ideal tank mates.


Harlequin Rasboras are a joy to have in any aquarium, thanks to their vibrant colors and peaceful nature. They are hardy, easy to care for, and readily available, making them a popular choice among fish keepers of all levels.

They also make excellent community fish, as they can peacefully coexist with a wide variety of species.

However, like all creatures, they have their unique needs and requirements.

But with a good understanding of these, you can create a thriving and vibrant environment for your Harlequin Rasboras, providing them with a happy and healthy life.