Harlequin Rasbora Care Guide: Simple Tips for a Happy Aquarium

Harlequin rasboras are magnificent, vibrant little fish that can bring life to any freshwater aquarium. With their striking appearance and entertaining demeanor, they’re sure to capture your heart. Caring for these beautiful fish isn’t as daunting as you might think, and with proper attention, they’ll thrive in your tank.

In this care guide, you’ll find everything you need to know about proper harlequin rasbora care, from tank mates to water parameters and feeding habits. By the time you’ve finished, you’ll have all the knowledge you need to ensure a healthy, happy environment for your harlequin rasboras.

So, get ready! You are about to embark on an exciting journey of adding these colorful fishes to your aquarium and enjoy the lively atmosphere they create.

Harlequin Rasbora Basics

Caring for Harlequin Rasboras can be a rewarding experience for both beginners and experienced aquarium enthusiasts. In this section, we’ll go over some basic information and care tips for these beautiful fish to help you maintain a healthy and thriving aquarium.

Species Overview

Property Information
Scientific name Trigonostigma heteromorpha
Common names Harlequin Rasbora, Harlequin Fish
Distribution Singapore, Malaysia, Sumatra, southern Thailand
Size Up to 2 inches (5 cm)
Lifespan 5-8 years
Diet Omnivorous; prefers small insects, crustaceans, and plant matter
Temperament Peaceful and schooling
Minimum tank size 10 gallons per 5-6 fish
Temperature 72°F to 81°F (22°C to 27°C)
pH 6.0 to 7.8
Water hardness 2 to 15 dGH
Care level Easy
Filtration/Water Flow Moderate
Water type Freshwater
Breeding Egg-scattering
Breeding difficulty Moderate
Compatibility Generally compatible with other small, peaceful fish species

Natural Habitat

Harlequin Rasboras thrive in slow-moving streams, rivers, and swamp areas with dense vegetation and dim lighting. They appreciate tanks mimicking this environment, including driftwood, rocks, plants, and subdued lighting. Your fish will be more comfortable swimming in groups, so we recommend keeping at least 5-6 Rasboras per 10-gallon tank.

Physical Appearance

Harlequin Rasboras have a laterally compressed body shape, with pinkish-orange to reddish-brown coloring and a distinctive triangular black patch that starts at the mid-section and slopes toward the caudal fin. Males usually have a more distinct and intense coloration and a slightly slimmer body than females. These stunning little fish will bring a vibrant touch to your aquarium.


Harlequin Rasboras typically have a lifespan of 5-8 years when properly cared for in a suitable environment. Their longevity in a freshwater aquarium can vary due to factors like genetics and tank conditions. Keep their tank clean and maintain correct parameters to ensure a longer, healthier life for your Harlequin Rasboras.

Tank Requirements

Proper tank requirements are essential for the health and well-being of your Harlequin Rasbora. In this section, we’ll guide you through selecting the appropriate tank size, maintaining the right water conditions, setting up your aquarium, and choosing the appropriate filtration. Let’s dive in!

Tank Size

Your Harlequin Rasbora will need ample space to swim and thrive. As a general rule, aim for a minimum tank size of 10 gallons, with about two rasboras per gallon of water. This means that a 10-gallon tank can comfortably house five rasboras, allowing them to live happily and healthily.

Water Conditions

It’s important to ensure your Harlequin Rasbora’s habitat has the right water conditions. Maintaining suitable water parameters helps promote their overall health and longevity. Aim for the following ideal water conditions:

  • Temperature: 72-78°F (22-25°C)
  • pH: 6-7.5
  • Hardness: 2-10 dGH

Regularly test the water parameters for ammonia, nitrite, and nitrate levels to ensure they remain within safe and stable limits.

Aquarium Setup

Creating a comfortable environment for your Harlequin Rasbora involves more than just the right water conditions. Consider the following factors when setting up your aquarium:

  • Substrate: Opt for a dark, soft substrate to mimic their natural habitat and make their vibrant colors stand out.
  • Plants: Include live plants for hiding spots, reducing stress, and promoting a healthy ecosystem in the tank.
  • Decorations: Add driftwood, rocks, and other hiding spots to provide an engaging environment for your rasboras to explore.


A good filtration system is essential for maintaining a clean and stable environment for your Harlequin Rasbora. Choose a filter that can handle the tank size and the number of fish you plan to keep. This will help to maintain optimal water quality and prevent the buildup of harmful toxins. Consider biological filtration options, as they facilitate beneficial bacteria growth to break down ammonia and nitrites, ensuring long-term water quality stability for your rasboras.

By carefully considering tank requirements, water conditions, aquarium setup, and filtration, you can create an ideal habitat for your Harlequin Rasbora, ensuring their overall happiness and well-being.

Diet and Feeding

Diet Composition

Harlequin rasboras thrive on a well-balanced diet, which includes a mix of high-quality pellets and flakes. Along with these, occasionally treat your fish with live or frozen foods like brine shrimp and bloodworms. Offering a varied diet ensures that they receive the essential nutrients that contribute to their overall health and well-being.

Feeding Frequency

Feed your harlequin rasboras once or twice a day, providing only as much food as they can consume within a couple of minutes. Overfeeding can lead to poor water quality and health issues for the fish. Regularly monitoring their feeding habits and adjusting the portion sizes accordingly ensures that your fish stay healthy and energetic.

Behavior and Temperament

Harlequin rasboras are peaceful, small tropical fish that make a great addition to your aquarium. They are schooling fish, meaning they thrive in groups of 8-10, creating a visually stunning display as they swim together.

When it comes to their sociability, harlequin rasboras prefer the company of their own species. However, they also get along well with other non-aggressive, similarly-sized tank mates. It’s important to provide a stress-free environment, as stress can lead to health issues for your fish.

To ensure a comfortable and engaging habitat, add plants, rocks, and hiding spots in your aquarium. This will allow them to exhibit their natural behaviors such as hiding and exploring. A well-planned tank setup will significantly contribute to the happiness and well-being of your harlequin rasboras, ensuring a harmonious community in your aquarium.

Compatible Tank Mates

When setting up your aquarium for Harlequin Rasboras, it’s important to keep a group of 8 to 10 individuals as they are shoaling fish. Make sure you have a spacious tank to accommodate the recommended group size, and ensure that their tank mates are small and non-aggressive species that share similar water parameters.

Some suitable tank mates for Harlequin Rasboras include:

  • Rummy Nose Tetra
  • Neon Tetras
  • Dwarf Gouramis
  • Cherry Barbs
  • Danios
  • Apistogramma
  • Cory Catfish
  • Honey Gourami
  • Other small Rasboras
  • Bolivian Ram
  • Mollies
  • Kuhli Loach

You may experiment with other small and peaceful tank mates, but it’s crucial to monitor their interactions to make sure everyone gets along. Harlequin Rasboras can also coexist with Betta fish if provided with an appropriate tank size and under watchful supervision.

These fish showcase their best behavior when kept in larger schools, even beyond the recommended group size. Harlequin Rasboras are peaceful by nature, and they don’t nip or quarrel with other species. You could also consider adding Cardinal Tetras and other small, non-predatory fish to enhance the beauty of your community tank.

Breeding Your Harlequin Rasboras

Breeding Harlequin Rasboras can be a rewarding challenge. To begin, you’ll want to select young, healthy specimens and condition them with live foods before attempting to breed.

Set up a breeding tank with appropriate water chemistry parameters and a temperature between 76-80°F. Introduce broad-leafed plants, as they will serve as a spawning location.

You’ll notice the breeding process start when the male performs a dancing and trembling display to attract the female. Once the female selects a suitable leaf, she will lay 6-12 eggs beneath it. This process may repeat, resulting in up to 300 eggs.

After spawning, quickly remove the adult fish to prevent them from consuming the eggs. The eggs will hatch in about 24 hours, and the fry will remain attached to the leaf, absorbing their yolk sac.

During the first 7-14 days, feed your fry with finely sized foods such as infusoria. You can then transition them to newly hatched brine shrimp or prepared commercial fry foods. Your Harlequin Rasboras will reach sexual maturity in about 6-9 months after hatching, and you can then enjoy your growing school of these beautiful fish.

Health and Disease

Caring for your Harlequin Rasbora also means keeping an eye on their health and being aware of potential diseases. In this section, we will discuss common illnesses, prevention, and treatment for your fish.

Common Illnesses

  • Ich (White Spot Disease): Caused by a parasite, Ich appears as small white spots on your fish’s body and fins. Fish with Ich may also exhibit rapid breathing and lethargy.
  • Fin Rot: A common bacterial infection, fin rot causes fins to appear frayed and discolored, often with a white or black edge. If left untreated, the infection can progress to the body.


To keep your Harlequin Rasbora healthy and prevent disease, follow these guidelines:

  • Maintain high water quality by performing regular water changes and testing the water parameters.
  • Do not overcrowd your tank, as this can cause stress and lead to poor water conditions.
  • Avoid rapid changes in water temperature and pH.
  • Quarantine new fish for at least two weeks before adding them to your main tank.
  • Feed your fish a varied and balanced diet to keep their immune system strong.


If your Harlequin Rasbora becomes sick, it is essential to act quickly. Here are some treatment methods for common illnesses:

  • Ich: Raise the water temperature to 82°F (28°C) for about a week, and treat the entire tank with an Ich medication following the product instructions.
  • Fin Rot: Use an aquarium antibiotic or antibacterial medication designed for fin rot treatment. Make sure to follow the dosing instructions provided by the manufacturer.

Remember to keep monitoring your fish during and after treatment, and always consult with an aquatic veterinarian if you are unsure about a diagnosis or treatment plan.

Frequently Asked Questions

What is the ideal water temperature for Harlequin Rasboras?

The ideal water temperature for Harlequin Rasboras is between 72 to 78 degrees Fahrenheit (22 to 25 degrees Celsius). Maintaining a stable water temperature within this range will help ensure your fish stay healthy and comfortable.

How many Harlequin Rasboras can comfortably live in a 20-gallon tank?

In a 20-gallon tank, you can comfortably house a school of about 10 to 15 Harlequin Rasboras. These fish prefer to live in groups and will thrive in an appropriately sized and well-maintained aquarium.

What is the average size of a Harlequin Rasbora?

The average size of a Harlequin Rasbora is between 1.5 and 2 inches (3.8 to 5 centimeters) in length. These small, brightly colored fish make an attractive addition to your freshwater aquarium.

What is the typical temperament of Harlequin Rasboras?

Harlequin Rasboras are peaceful and sociable fish that generally get along well with other non-aggressive tank mates. They have a calm demeanor and will exhibit interesting group behaviors when part of a school.

What is the minimum tank size needed for Harlequin Rasboras?

The minimum tank size recommended for Harlequin Rasboras is 10 gallons. However, a larger tank is always preferable, as it provides more space for your fish to swim and interact with their environment.

Do Harlequin Rasboras prefer bright or dim lighting?

Harlequin Rasboras prefer a moderate level of lighting in their aquarium. Not too bright, but not too dim either. It’s essential to balance the lighting to help maintain a healthy environment for your fish while also allowing them to display their vibrant colors.