Harlequin Rasbora

Harlequin Rasboras are fascinating freshwater fish and a notable relative to Danios. Boasting an appealing orange color along with a distinct black 'wedge' on their tail, they have won the hearts of aquarium hobbyists. These amiable fish necessitate modest maintenance, rendering them a prime choice for community tanks.

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Care DIfficulty


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Southeast Asia

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2 inches (5 cm)

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5 to 8 years

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Table of contents

Origin, Appearance, Size, and Lifespan

The Harlequin Rasbora, or Trigonostigma heteromorpha, frequently referred to as the Red Rasbora, is a favored freshwater fish originating from the Malay Peninsula, Singapore, and Sumatra in Southeast Asia. They are typically found in slow-moving streams or peat swamps, thick with vegetation.

In their natural habitat, Harlequin Rasboras predominantly inhabit tranquil, shallow waters with an abundance of aquatic plants. These plants act as both concealment and a food source, while the dark swamp floors accentuate their vibrant colors. These sociable fish prosper in groups of no less than six, though it's not unusual to see them in schools of 20 or more.

Their natural environment comprises warm, slightly acidic water. The temperature generally fluctuates between 72 to 81 degrees Fahrenheit (22 to 27 degrees Celsius), with a pH level of 5.0 to 7.0, and water hardness between 1 to 10 dGH. To emulate a similar environment in your aquarium, ensure a steady water temperature, utilize a high-quality filtration system, and include live plants and driftwood.

By accurately reflecting the Harlequin Rasbora's natural environment and preserving the right water conditions, you'll be establishing a healthy and contented life for your fish within your aquarium.

Harlequin Rasboras are appreciated for their brilliant orange bodies, accented by a unique black 'wedge' at the tail end. These vibrant hues make them an engaging and attractive element in aquariums. Although they are petite, attaining a size of roughly 2 inches (5 cm), their distinguishing colors and energetic disposition make them a perfect choice for those desiring a lively, colorful aquatic display. These endearing fish captivate observers as they energetically swim through the tank, positioning them as a beloved favorite among hobbyists of varying expertise levels.

With attentive care, Harlequin Rasboras can live up to 5 to 8 years. As social creatures, they thrive in groups and are best kept in schools of at least six individuals. To support their health and longevity in captivity, it's crucial to offer a richly planted aquarium with plenty of hiding spaces, along with a varied diet of high-quality flakes, pellets, and occasional live foods.

Fun Facts

Now that we've delved into the appearance and lifespan of Harlequin Rasboras, we'll spotlight some compelling facts about these vibrant fish that set them apart in the aquarium community. From their distinctive markings to their collective behavior, Harlequin Rasboras are brimming with marvels that will undoubtedly charm any fish keeper.

  • Color-changing properties: Harlequin Rasboras have a unique ability to modify their color intensity depending on their environment, emotional state, or health status. Under low light conditions or during stressful times, their colors may seem less radiant. However, when they feel safe and are in good health, their hues become more luminous, allowing them to become a focal point in any aquarium setting.
  • Adaptive camouflaging: In their natural habitat, Harlequin Rasboras' unique black 'wedge' shape on their bodies acts as an adaptive camouflage, helping them hide from predators. This marking blends with the shadows cast by aquatic plants, creating an optical illusion and increasing their survival chances.
  • Cyprinidae family ties: Despite their distinctive coloration, Harlequin Rasboras are closely related to carp and minnows (family Cyprinidae). Yet, they've developed bright colors and unique markings for communication and camouflage in their native habitats.
  • Group dynamics: Harlequin Rasboras are schooling fish, preferring to move around in groups. This behavior not only provides a sense of security but also crafts a captivating visual spectacle in an aquarium. Their synchronized movements and bright colors can turn a domestic aquarium into an alluring aquatic display.
  • Reproduction quirks: Unlike many other freshwater fish, Harlequin Rasboras have a unique way of laying eggs. The female deposits her eggs on the underside of broad-leaved plants, and the male, in turn, fertilizes them. This unusual breeding behavior adds another interesting facet to their already engaging character.

With these captivating facts about Harlequin Rasboras at your fingertips, you're better equipped to understand and appreciate their charm and complexity in your aquarium. In the subsequent section, we'll offer advice on tank setups, guaranteeing your Harlequin Rasboras have an ideal environment to thrive and exhibit their vibrant features.

Recommended Tank Setups

Every setup incorporates essential elements—tank, filter, heater, lighting, substrate, etc.— to create a suitable environment for Harlequin Rasboras and other compatible freshwater fish species in your aquarium. As you progress from economical to luxurious setups, you'll find more avenues for customization, aesthetic enhancements, and state-of-the-art features. Harlequin Rasboras are schooling fish that thrive in groups of at least six, to lower stress levels and promote their well-being. Generally, Harlequin Rasboras cost between $2 and $4 per fish, but prices can fluctuate based on aspects like size, quality, and availability.

Budget-friendly setup (approximately $200):

  • Tank: 20-gallon aquarium with a cover or glass canopy ($40 - $70)
  • Filter: Hang-on-back (HOB) or sponge filter rated for 20 gallons ($20 - $40)
  • Heater: 50-100 watt adjustable aquarium heater ($15 - $30)
  • Lighting: Basic LED aquarium light ($20 - $50)
  • Substrate: Economical aquarium sand or small pebbles ($10 - $20)
  • Decor: A few bits of driftwood and stones, along with budget-friendly live plants like Java Moss and Anubias ($20 - $40)
  • Fish: Minimum 6, maximum 10 Harlequin Rasboras ($20 - $30)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

Mid-range setup (around $400 - $650):

  • Tank: 20-30 gallon aquarium with a hood or glass canopy ($60 - $120)
  • Filter: Canister filter or top-grade HOB filter rated for the tank size ($60 - $150)
  • Heater: 100-150 watt adjustable aquarium heater ($25 - $50)
  • Lighting: LED aquarium light with adjustable settings for promoting plant growth and enhancing color ($50 - $150)
  • Substrate: Nutrient-enriched aquarium substrate designed for planted tanks ($20 - $40)
  • Decor: A blend of driftwood, stones, and live plants such as Amazon Swords, Java Moss, Anubias, and Cryptocoryne species ($40 - $80)
  • Fish: Minimum 6, maximum 15 Harlequin Rasboras ($20 - $50)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

High-end setup (above $800):

  • Tank: 30-40 gallon rimless aquarium with a glass canopy ($120 - $250)
  • Filter: Premium canister filter rated for the tank size ($100 - $250)
  • Heater: 150-200 watt adjustable aquarium heater with an external temperature controller ($40 - $80)
  • Lighting: Advanced LED lighting system with customizable settings for plant growth, color enhancement, and day/night cycles ($150 - $300)
  • Substrate: Premium aquarium substrate designed for planted tanks, with added root tabs for supplementary plant nutrition ($30 - $60)
  • Decor: An amalgamation of driftwood, rocks, and live plants to form a natural aquascape, featuring plant species such as Amazon Swords, Java Moss, Anubias, Cryptocoryne species, and carpeting plants like Dwarf Hairgrass or Monte Carlo ($60 - $150)
  • Fish: Minimum 6, maximum 20 Harlequin Rasboras ($20 - $70)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

Please keep in mind that these figures are just suggestions. Factors such as tank mates and individual fish personalities should be considered when determining the number of Harlequin Rasboras to accommodate in your aquarium. Prices may vary depending on location, brand, and availability.

Set Up Your Tank

After familiarizing ourselves with the suitable tank setups for Harlequin Rasboras, let's now delve into the systematic procedure of setting up the aquarium. The subsequent instructions will help you in selecting an ideal spot for your tank, tank cleaning and preparation, equipment installation, water cycling, and proper fish acclimation. By abiding by these steps, you can establish a vibrant aquatic home for your Harlequin Rasboras to thrive in.

  • Step #1: Start by determining an ideal location for your tank. Ensure it is away from direct sunlight, sources of heat, and drafty areas. The chosen spot should be sturdy and level to support the weight of your filled tank. If you need a stand for the aquarium, assemble it as per the manufacturer's guide, then place your tank on it.
  • Step #2: Now, clean the tank. Rinse it with water (do not use soap or detergents) to get rid of any dust or residual debris. Wipe its interior using a clean, soft cloth or paper towel. Also, rinse your substrate (either sand or gravel) thoroughly until the water is clear, then spread it at the bottom of the tank. Create a slight slope toward the back for a sense of depth.
  • Step #3: Prior to filling the tank with water, plan your aquarium layout. This involves deciding the placement of your filter, heater, and other equipment. This preplanning step can significantly ease your setup and maintenance tasks. Install your heater and filter as per the guidelines provided by the manufacturer. If you opt for a sponge or under-gravel filter, position it beneath the substrate before you add water.
  • Step #4: Decorate your tank using plants, driftwood, and rocks to create hiding spots for your fish while also enhancing the aesthetics of the tank. Make sure to keep ample open swimming spaces for your Harlequin Rasboras. Arrange your decorations carefully so as not to hinder or damage your equipment. Anchoring plants to rocks or driftwood can also help keep them in place.
  • Step #5: Fill your tank with water treated with a dechlorinator if your tap water contains chlorine or chloramines. Place a clean plate or bag on the substrate to prevent disruption while filling the tank. When the tank is about 2/3 full, attach your aquarium light following the manufacturer's instructions. Maintain a regular day-night cycle with the help of a timer for your aquarium light. Connect your heater, filter, and any other equipment (like an air pump or CO2 system) to power sources and position the thermometer where it can be easily seen.
  • Step #6: Top off the tank with water, leaving some space between the water surface and the tank's top for oxygen exchange. Power on the filter, heater, and other devices. Adjust the heater to maintain the right water temperature. Let the tank cycle for 4-6 weeks to establish beneficial bacteria and stabilize water parameters. During this cycling process, adding bacterial starter culture can expedite the development of beneficial bacteria. Keep an eye on the ammonia, nitrite, and nitrate levels using an aquarium test kit.
  • Step #7: After the cycling phase and when the water parameters are stable, acclimate your Harlequin Rasboras before introducing them into the tank. Start by floating the bag with the fish in the tank for about 15-20 minutes to equalize temperatures. Then, gradually introduce a small quantity of tank water into the bag. Continue this process every 5-10 minutes for a minimum of 30-60 minutes to help the fish gradually adjust to the new water chemistry. Use a net to gently transfer the fish into the tank, reducing unnecessary stress or exposure to the bag water.
  • Step #8: When the fish have been introduced, establish a regular feeding schedule, providing high-quality food suitable for Harlequin Rasboras. Perform water changes of 20-30% every 1-2 weeks and regularly monitor water parameters. Keep a close eye on your fish for any signs of stress or illness, especially during the initial weeks post introduction. If required, make adjustments to water parameters or seek professional advice.

By adhering to this comprehensive guide and integrating the mentioned setup tips, you'll be able to create a healthy and vibrant aquatic environment where your Harlequin Rasboras can thrive.

Recommended Water Parameters

Creating the ideal environment for your Harlequin Rasboras begins with maintaining the right water parameters in your tank. Here are the key elements to consider:

  • Temperature: Aim for a comfortable water temperature between 72°F and 81°F (22°C and 27°C).
  • pH: Harlequin Rasboras thrive in slightly acidic to neutral water conditions, so a pH between 6.0 and 7.5 is perfect.
  • Hardness: Opt for moderately soft to moderately hard water within the range of 2-15 dGH.
  • Ammonia, Nitrite, and Nitrate: As with all fish, aim to keep ammonia and nitrite levels at 0 ppm, and try to maintain nitrate levels below 20 ppm.
  • Lighting: Moderate lighting suits Harlequin Rasboras, but providing shaded areas via plants or decorations can reduce stress.
  • Water movement: A moderate current that mimics their native slow-moving streams and rivers is ideal.Regular water testing and necessary adjustments will ensure a stable and comfortable environment for your fish.

Routine Water Maintenance

To maintain optimal water conditions, regular cleaning and maintenance of your Harlequin Rasbora tank is essential. Here's a suggested regimen:

  • Weekly water changes: Swap out around 20-30% of the tank water every week.
  • Test water parameters: Regularly check your tank's pH, ammonia, nitrite, nitrate, and hardness levels.
  • Use a gravel vacuum: This tool helps clean the substrate during water changes.
  • Dechlorinate the water: If using tap water, a water conditioner is necessary to remove harmful chemicals.
  • Match temperature and pH: Ensure that the newly added water matches the existing tank water in both temperature and pH.
  • Acclimate the fish: After a water change, give your fish time to adapt to the new conditions.In addition to this, other important tasks include:
  • Monitor lighting duration: Maintain a consistent lighting schedule of approximately 10-12 hours daily, as excess light may trigger algae growth.
  • Plant maintenance: Trim live plants regularly to maintain their health and appearance, removing any dead leaves or plant material.
  • Filter maintenance: Keep your filter clean and replace the media as instructed by the manufacturer, usually every month or so.

Diet and Feeding Schedule

Harlequin Rasboras are omnivores, meaning they require a varied diet for optimal health. Here are some suggestions:

  • Flakes and pellets: Use high-quality tropical fish flakes or pellets as their primary diet.
  • Frozen and live foods: Treat your Harlequin Rasboras with brine shrimp, daphnia, or bloodworms occasionally.
  • Vegetable matter: Offering blanched vegetables like spinach or peas provides additional nutrients.
  • Feeding frequency: Two to three small feedings per day are recommended, being careful to avoid overfeeding.

Stress and Diseases

Like any other fish species, Harlequin Rasboras may experience stress due to sub-optimal water conditions, aggressive tank mates, or other environmental factors. Recognizing and rectifying these stressors is crucial for their well-being:

  • Watch for stress signs: Pay close attention to your Harlequin Rasboras for signs of stress such as erratic swimming, color loss, lethargy, or loss of appetite.
  • Check water quality: Regular water testing can help detect any issues with water parameters promptly.
  • Monitor tank mates: Keep a vigilant eye on the behavior of other fish in the tank to ensure your Harlequin Rasboras aren't being bullied.
  • Create a suitable habitat: Provide adequate hiding spaces and ensure the tank size is appropriate for your fish.

Harlequin Rasboras, while generally resilient, can suffer from common fish diseases such as:

  • Ich (white spot disease): Symptoms include white spots on the body and fins, lethargy, and loss of appetite. Treatment typically involves aquarium salt or anti-parasitic medication, and a slight increase in water temperature.
  • Fin rot: This bacterial disease manifests as frayed or discolored fins and can be treated with a partial water change and antibacterial medication.
  • Velvet disease: Look out for a yellow or gold dust-like coating on the fish's body. It's a parasitic infection that can be addressed with anti-parasitic medication.
  • Swim bladder disease: Fish struggling to swim upright may have this condition. Fasting and a diet of blanched peas can be effective treatments.

Maintaining excellent water quality, proper feeding, and a stress-free environment can prevent most diseases. Any new fish should be quarantined before introducing them to the tank.


Breeding Harlequin Rasboras can be a fulfilling undertaking for the aquarist. Follow these steps for a successful breeding endeavor:

  • Step #1: Set up a breeding tank with the right conditions - a pH of about 6.0, a temperature of around 80°F (27°C), soft water, and the inclusion of broad-leaved plants or a spawning mop.
  • Step #2: Choose a healthy, mature pair for breeding. The males tend to be smaller and slimmer with a more rounded caudal peduncle, while the females are more full-bodied.
  • Step #3: Enhance the fish's health and readiness to breed by providing a protein-rich diet for a few weeks before the breeding period.
  • Step #4: Encourage spawning by placing the chosen pair in the breeding tank, gradually raising the temperature, and reducing the lighting. The female will lay eggs on the underside of the broad-leaved plants or spawning mop.
  • Step #5: Post-spawning, remove the parent fish to protect the eggs. The eggs will hatch in about 24-36 hours, and the fry will start swimming in about three days. Initially, feed them infusoria or liquid fry food, then gradually introduce micro-worms or brine shrimp nauplii.
  • Step #6: Keep an eye on the fry's growth and development, and segregate them by size if necessary to prevent cannibalism.

Patience, meticulous care, and the right conditions are vital for breeding Harlequin Rasboras successfully.

Recommended Tank Mates

Here are the top 10 suggested companions for Harlequin Rasboras:

  1. Gouramis
  2. Neon Tetras
  3. Cherry Barbs
  4. Endler's Livebearers
  5. Zebra Loaches
  6. Corydoras Catfish
  7. Amano Shrimp
  8. Mystery Snails
  9. Platies
  10. Ghost Shrimp

Keep in mind to avoid bigger, predatory fish such as cichlids, oscars, or aggressive species as they may pose a threat to Harlequin Rasboras. Always monitor the behavior of new fish to ensure they are not causing any stress or displaying aggression towards the Harlequin Rasboras.


In conclusion, Harlequin Rasboras are an appealing species of freshwater fish known for their vibrant colors and easy care. These fish require specific water conditions, a balanced diet, and an appropriate environment to flourish. With proper care, they can live up to 6-8 years and can be a remarkable addition to any community tank. Choosing tank mates is crucial and should consist of peaceful and non-aggressive species for a balanced aquarium environment. Breeding Harlequin Rasboras can be a rewarding experience, though it calls for ideal conditions and patience. Overall, Harlequin Rasboras can amplify the beauty of any aquarium with their lively behavior and striking color patterns.

Frequently Asked Questions

What is the ideal tank size for Harlequin Rasboras?

A 10-gallon tank is considered the minimum for Harlequin Rasboras, but a 20-gallon tank or larger is recommended for a school of them, which allows for stable water conditions and ample swimming space.

How many Harlequin Rasboras should be kept together?

Harlequin Rasboras are schooling fish and should be kept in groups of at least 6 to 10. A larger school encourages their natural behavior and makes them feel more secure.

What water parameters do Harlequin Rasboras require?

Harlequin Rasboras thrive in water temperatures between 72°F and 81°F (22°C and 27°C), a pH between 6.0 and 7.5, and moderately soft to moderately hard water with a hardness between 2 and 15 dGH.

What do Harlequin Rasboras eat?

Harlequin Rasboras are omnivores and appreciate a variety in their diet. Feeding them a blend of high-quality flake or pellet food, along with live or frozen foods like daphnia, brine shrimp, and bloodworms is recommended.

Are Harlequin Rasboras compatible with other fish?

Yes, Harlequin Rasboras are generally peaceful and can live peacefully with other similarly-sized, non-aggressive fish species. Ideal tank mates include small tetras, other rasboras, corydoras catfish, and small shrimp species.

How long do Harlequin Rasboras live?

With the right care and optimal tank conditions, Harlequin Rasboras can live for about 6-8 years.

How do I breed Harlequin Rasboras?

Breeding Harlequin Rasboras requires specific conditions like a separate breeding tank, correct water parameters, and suitable food for the fry. Males and females should be separated before introducing them for spawning.

Do Harlequin Rasboras require a planted tank?

While they can survive without live plants, a planted tank is recommended for Harlequin Rasboras. Live plants provide hiding spots, improve water quality, and simulate a natural environment similar to their native habitat.

Can Harlequin Rasboras change color?

Yes, Harlequin Rasboras can change color due to several factors such as stress, illness, or changes in water conditions. If you notice color loss in your Harlequin Rasboras, check your water parameters and monitor their health closely.