Harlequin Rasbora: Care, Size, Lifespan, Diet & More

Harlequin Rasbora (Trigonostigma heteromorpha) is a peaceful and active schooling fish that makes an excellent addition to any freshwater aquarium. They are known for their vibrant yet unique body patterns. These fish are also known as Red Rasbora in some places.

These fish have a friendly disposition towards other tank mates, making them ideal community fish. They are also very easy to care for when you know their basic needs. 

In this article, you will be provided with the proper steps to take to properly care for a Harlequin Rasbora as well as any other relevant information.

Species Profile & Overview

The Harlequin Rasbora is a species of fish native to Southeast Asia. It inhabits shallow rivers and streams with sandy or muddy bottoms, clear water, and plenty of vegetation. 

These areas usually have slow to moderate currents and provide the fish with ample hiding places among plants and other aquatic life.

Harlequin Rasboras are peaceful schooling fish that prefer to stay in groups of five or more individuals. They will often swim together near the middle and close to the surface in search of food while avoiding predators. 

The males tend to be slightly larger than females but both sexes display similar behaviors such as fin-nipping when they feel threatened or stressed out by their environment.

Harlequin Rasboras are popular among aquarium hobbyists due to their attractive coloration which consists of an orange body highlighted by a black triangular patch on each side of their body. 

They also require minimal care making them ideal for beginner aquarists who want something easy yet beautiful in their tanks! Additionally, these hardy little fish can adapt well to different tank conditions so long as there is adequate filtration and regular water changes are performed.


School of Harlequin Rasbora
School of Harlequin Rasbora

The Harlequin Rasbora fish is a stunningly beautiful species of freshwater fish that stay small in size. It has an eye-catching coloration with its body featuring a deep black and orange pattern, which makes it one of the most popular aquarium fish around. 

The unique shape features of this species include its short, rounded head and long fins that fan out from the sides. The colors and patterns on these fish are quite similar, they have a yellowish orange body with a black triangular shape on their body.

They also have several variations in their fin shapes; some may have shorter fins while others may be more elongated or even split into two parts at the tips. No matter what variation they come in, all Harlequin Rasboras possess a distinctively beautiful appearance when swimming through an aquarium. 

The fins on long-fin variations look especially striking against their bodies as they move gracefully through the water column with each wave of their tail adding to their beauty and charm. 

The combination of vibrant orange colors of the fins along with graceful movements make them an absolute pleasure to watch as they swim around your tank! 

Not only do these lovely creatures bring life and vibrancy to any aquarium setup but they also provide hours upon hours of entertainment for both novice aquarists and experienced hobbyists alike!

Adult Size

The Harlequin Rasbora is a small fish, typically growing to around 2 inches in length. Males and females are similar in size, with males usually being slightly larger than females. 

The smaller size of these fish makes them ideal for aquariums of all sizes, as they will not take up too much space or require large tanks. Most people use these fish in nano tanks or smaller tanks.

Due to their bright coloration and active swimming behavior, they look great when kept in schools that move together through the water column. This gives off a unique sense of movement that can be quite captivating to watch! 

Overall, the relatively small size and vibrant colors of Harlequin Rasboras make them an excellent choice for any type of aquarium setup!


The Harlequin Rasbora typically lives between 5 and 8 years. However, the lifespan of an individual Harlequin Rasbora can be affected by several factors, including water quality, diet, stress levels, tank size, and temperature.

Water quality plays an important role in determining the lifespan of a Harlequin Rasbora. Poor water conditions can lead to disease or other health problems which may shorten its lifespan. 

To ensure optimal water quality for your Harlequin Rasboras it is important to maintain regular partial water changes and use high-quality filtration systems to keep their environment clean and healthy.

A balanced diet is essential for any aquarium fish but especially so for the Harlequin Rasbora as they are omnivores with specific dietary needs. Providing adequate nutrition will help promote long-term health and extend their life expectancy significantly. 

Stress can also have a major impact on the lifespan of any fish species including the Harlequin Rasbora Fish.

Behavior & Temperament

Harlequin Rasboras are peaceful, schooling fish that prefer to be kept in groups of six or more. They are active and social, swimming around the tank in a large school. 

Harlequin Rasbora fish are great community tank fish. These fish get along well with other small peaceful fish; However, they should not be housed with larger aggressive species such as Cichlids or Goldfish which may bully them.

It is also important to provide adequate space for each fish so that it can swim freely without feeling crowded or threatened by other tank mates.

They prefer to live in large groups of at least six individuals, but ideally more than that. In the wild, they form schools of hundreds or even thousands of fish. These schools provide safety from predators as well as a way to find food sources quickly and efficiently. 

When kept in an aquarium, Harlequin Rasboras should be kept in groups of at least 5 – 6 individuals. This way they can feel secure and comfortable enough to display their natural schooling behaviors. 

With proper care and maintenance, these beautiful little fish can live a long life in captivity and will be sure to bring joy to their owners for many years to come!

Harlequin Rasbora Care

Harlequin Rasbora fish is an ideal choice for a home aquarium due to their ease of care and peaceful nature. These small fish will benefit from plenty of hiding places such as plants, driftwood, rocks, and caves to help them feel secure in their environment. 

Harlequin Rasbora fish are highly adaptable and can tolerate a wide range of water parameters. This is important because it allows aquarists to easily match the conditions of their tank to what the Harlequin Rasboras would experience in the wild. 

Additionally, this adaptability also makes them a great choice for beginner aquarists who may not have experience with maintaining specific water parameters or creating a specialized environment for their fish.

Tank Size

The minimum tank size for a Harlequin Rasbora fish is 10 gallons. This species of fish prefers to live in groups, so it is recommended that at least 5 – 6 of them be kept together in the same tank. The larger the group, the more comfortable and less stressed they will be. 

When keeping this species in smaller tanks, it is important to provide plenty of hiding places such as plants or decorations to reduce stress levels. Additionally, regular water changes are necessary for these fish since they are sensitive to poor water quality and ammonia buildup can occur quickly with too few water changes.

However, having a larger tank will give them more space to swim around and show their schooling behaviors. A large aquarium can allow the fish to have more space to swim, explore and play. 

What To Put In A Harlequin Rasbora Tank

To decorate the aquarium for Harlequin Rasbora fish, you can create a well-planted aquascape with plenty of hiding places. This species prefers an environment that is densely planted and has lots of driftwood or rocks to provide cover. 

Harlequin Rasbora fish need a variety of decorations in their tank to provide them with hiding places and a sense of security. Decorations such as rocks, driftwood, plants (real or artificial), and other structures will help create areas where the fish can hide from potential predators. 

These decorations can also be used to break up line-of-sight within the aquarium so that the Harlequin Rasboras feel more secure when swimming around.

The best types of decoration for these fish are real plants, rocks, and driftwood. Natural decorations are a great way to make your aquarium look more beautiful and natural. They provide a variety of benefits over artificial decorations.

Natural decoration will make the tank aesthetically pleasing for humans and the fish living in the tank. The colors and textures of real plants, rocks, driftwood, and other natural materials add visual interest to the tank that can’t be replicated with plastic ornaments. 

The substrate is an important part of any aquarium, but it can be especially beneficial for a Harlequin Rasbora aquarium. Substrate helps to keep the water clean by trapping debris and detritus and it also serves as a home for beneficial bacteria that help break down waste in the tank.

The best type of substrate for a Harlequin Rasbora is a darker-colored substrate that can help bring out the vibrant colors of these fish. Lighter-colored substrates may make them look duller in comparison. You can pick sand or fine gravel with rounded edges so that the plants can easily root in it.

Speaking of plants, they are essential for a healthy and balanced aquarium environment. They provide oxygen, balance out pH levels, absorb carbon dioxide, reduce nitrate levels, and create hiding places for fish. 

Harlequin Rasboras in particular benefit from the presence of plants as they enjoy grazing on algae that grow on plant leaves. Plants also help to soften the light in an aquarium which can be beneficial for shy fish like Harlequin Rasboras who may feel more secure when there are plenty of covers available.

Aquatic plants that are compatible with Harlequin Rasbora fish include Anacharis, Moneywort, Rotala Indica, Water Sprite, and Jungle Val. These plants are easy to care for and can make a tank look lush green. 

You can also add some floating plants like Amazon Frogbit or Dwarf Water Lettuce to give them more shade and security. Generally speaking, these fish are not peaky when it comes to the types of plants you want to add to their tank as long as they are not artificial.

School of Harlequin Rasbora
School of Harlequin Rasbora

Light Requirements

Harlequin Rasbora fish need bright but indirect light to look their best. High-quality lights will bring out the vibrant colors of the fish and help them stay healthy. These lights will also increase photosynthesis in plants resulting in better nutrient absorption, and improved growth rate.

The right type of light can also affect the colors of your Harlequin Rasbora. The brighter full-spectrum lights will bring out their vibrant red and orange coloration, while dimmer lighting may cause them to appear more dull or grayish.

To buy the right light for your Harlequin Rasboras, look for full-spectrum LED lights with adjustable intensity settings so you can adjust the brightness as needed. This will help ensure your fish display their best colors all day long!

Water Conditions & Parameters

These fish prefer water parameters that match their natural habitat. It is important for their health and well-being as it allows them to live comfortably. 

Harlequin Rasboras are native to slow-moving streams and rivers in Southeast Asia. In their natural habitat, they live in blackwaters with very stable parameters. 

Matching the aquarium water parameters to these levels will help ensure that your Harlequins remain healthy and thrive in captivity.

Below is the ideal range of parameters for Harlequin Rasbora in captivity:

  • Temperature: 72 – 81 Degrees Fahrenheit
  • pH: 6.5 – 7.2
  • TDS: 50 – 150 PPM

Stable parameters are much more important than chasing specific numbers. By changing the water in an aquarium weekly, you are ensuring a healthy environment for your fish. This helps to maintain a balanced environment and remove toxins that can build up over time.

Filtration System

Harlequin Rasbora fish need a strong filtration system that does not create fast flow in the tank. These fish are small and sensitive to water quality and can be easily affected by poor water conditions. 

A good filter will help to maintain beneficial bacteria in the tank that is necessary for breaking down waste produced by the fish. 

When picking a filter for an aquarium, it is important to consider factors such as size, flow rate, type of media used (mechanical or biological), noise level, cost, and maintenance requirements.

We recommend a canister filter or a sponge filter for Harlequin Rasboras as they need a clean and stable environment. These filters are easy to maintain and can house a lot of beneficial bacteria. 

Common Diseases and Prevention

Harlequin Rasbora fish are susceptible to a variety of aquarium diseases, including bacterial infections, parasites, and fungal infections. Bacterial infections can cause ulcers on the skin or fins, cloudy eyes, and fin rot. 

Parasites such as ich (white spot disease) can cause white spots on the body and fins. Fungal infections can result in discoloration of the skin or lesions on the body or fins. These diseases can have a significant effect on Harlequin Rasbora’s health if left untreated. 

In extreme cases, these diseases may even be fatal for your fish if not treated quickly enough with appropriate medications.

Poor water quality can cause disease in aquariums by allowing harmful bacteria and other pathogens to thrive. Poor water quality can also lead to the accumulation of toxins, such as ammonia and nitrites, which are toxic to fish.

To prevent diseases in an aquarium, it is important to maintain good water quality through regular partial water changes and filtration. It is also important to monitor pH levels and keep them within the ideal range for your particular species of fish. 

Finally, quarantine new fish before introducing them into your existing tank environment. This will help reduce the risk of spreading any potential illnesses from one fish to another. 

Diet and Feeding Requirements

Harlequin Rasbora fish are omnivores. In the wild, they feed on a variety of food sources including insects, larvae, worms, small crustaceans, and algae. They also feed insect eggs and other organic matter that floats on the surface or in the water.

In captivity, they should be fed a variety of foods including high-quality flakes or pellets, freeze-dried bloodworms, and brine shrimp. Ideally, feed your Harlequin Rasboras twice daily with small amounts of food that can be consumed within 2 minutes. 

Feeding a mix of dry and frozen foods to Harlequin Rasbora fish is beneficial for their health. Dry foods are an excellent source of carbohydrates, proteins, vitamins, minerals, and other essential nutrients that help keep the fish healthy. 

Frozen foods provide additional sources of protein and fat which are beneficial for the growth and development of the fish. The combination of frozen and dry types of food helps to ensure that the fish receive a balanced diet with all the necessary nutrients they need to stay healthy.

Avoid overfeeding as this can lead to water quality issues and health problems for your fish. Remove any uneaten food after feeding time has elapsed to keep the tank clean and healthy.

Breeding Harlequin Rasbora

Breeding Harlequin Rasbora fish in an aquarium is not easy but can be done. First, it is important to make sure that the tank has plenty of hiding places for the adults and the fry.

A well-planted tank with some floating plants such as Java moss will provide an excellent bet for adults to lay their eggs on. It’s also important to keep the water temperature slightly higher to encourage them to breed. 

The pH should be slightly acidic at around 6.5 and hardness should be kept low. They should receive food more often and the food should have higher protein content. 

Harlequin Rasbora fish are egg scatterers, meaning they lay their eggs in the water and do not provide any parental care. The female will lay her eggs on a flat surface such as a leaf or rock, and then both parents will swim away. 

Harlequin Rasboras can lay up to 100 eggs each time they breed. The female will lay her eggs in batches, with each batch containing between 10 and 20 eggs. Once eggs are laid, it’s best to remove the parents from the breeding tank.

After this process is complete, the fry will hatch within 1 – 2 days and begin swimming around on their own. Make sure to have some baby brine shrimp ready so your baby Harlequins can have something to feed.

Tank Mates

These fish are peaceful and can be kept with other tank mates of similar size. They prefer to school in groups, so it is best to keep them with their kind in large numbers. 

In a larger tank, you can also mix them with other fish that share a similar personality and need a similar environment. If kept in smaller tanks, the Harlequin Rasboras may become stressed due to lack of space and overpopulation. 

Providing adequate space is also essential for these fish to display natural behaviors such as schooling and playing with one another. Having a peaceful larger fish can enhance their schooling behaviors.

Considering these, here are our top picks of tank mates for Harlequin Rasbora:

School of Harlequin Rasbora
School of Harlequin Rasbora


Harlequin Rasbora fish are a great addition to any aquarium. They are peaceful, colorful, and hardy fish that will bring life and beauty to your tank. Their unique coloration is unlike any other species of fish in the aquarium hobby, making them stand out from the crowd. 

They also require minimal care and can thrive in most water conditions as long as they have plenty of hiding places for security. With proper care and maintenance, these beautiful little creatures can be a joy to keep for many years!