how to care for harlequin rasbora

Looking for a striking, spunky little fish with loads of energy? Then look no further than this darling little guy, the Harlequin Rasbora.

The colorful species is pretty chill and easy to care for, making them a great option for newbie hobbyists or long-term aquarists alike.

Quick Intro to Harlequin Rasbora

Family: Cyprinidae
Scientific Name: Trigonostigma heteromorpha
Other Names: Red Rasbora, Harlequin Fish, and Harlequin. Color variations are sometimes called Black Harlequin Rasbora, Blue Harlequin Rasbora, and Gold Harlequin Rasbora
Care Level: Easy

Natural Habitat, Identification, and Where to Buy

Harlequin Rasbora

Harlequin Rasboras are tropical fish that belong to the Cyprinidae family. Harlequin is a very popular species used in home aquariums.

They are native to Asia and most often they are seen in Singapore, Thailand, and Malaysia. They live in a variety of streams, rivers, and swamp forests that are similar to the blackwater rivers of South America.

Harlequins are small fish that are easy to care for. It is a peaceful breed of fish that isn’t aggressive or will nip at the fins of other fish.

This is a great choice for those who are getting into the hobby and want a fish that won’t cause them too many troubles.

They spend the majority of their time in the middle later of the water. It is rare to see them swim up to the surface or down to the substrate. If you see them hiding among plants or other objects, they may be stressed and need help.

By having other members of their species, they will form shoals and swim around together. This is enough to reduce the majority of the stress the fish may have.

Author note: Another plus side to choosing to use Harlequins is that due to their popularity they are carried in almost every aquarium store that sells fish. On average you can expect to pay around $2-$4 per fish.

Optimal Water Conditions for Harlequin Rasbora

Water Temperature: 72°F – 80°F
Water Flow Rate: Slow
pH: 5.5 – 7.0
Water Hardness: Up to 12 dGH

Tank Setup for Harlequin Rasbora

Rasbora Het Harlequin rasbora heteromorpha freshwater aquarium fish
Rasbora Het Harlequin rasbora heteromorpha freshwater aquarium fish
Minimum Tank Size: 10-gallon tank
Optimal Tank Size: 15 gallons
Optimal Tank Shape: Rectangle/Square
Recommended Filter Type: High-quality HOB

When you are planning your tank for Harlequins, remember that they are fish that is easy for beginners to take care of. This is a hardy fish that can handle more than the average aquarium fish.

Author note: They are tolerant of a range of tank conditions and do not suffer when there are slight fluctuations in temperature.

Despite how resilient Rasboras are, they can’t just be placed in any tank with any kind of water or settings. Every fish has ideal parameters that they need to survive and thrive.

The most important part of any successful tank is the water. Your fish will live, breathe, play and experience all of their fishy lives in water so it needs special care.

This species belongs to the family of fish that are freshwater. This species will never be seen in brackish waters and can’t survive in them.

When you are deciding on the water it is helpful to look at where this fish comes from. Their native habitat involves lowland waters in southeastern Asia. This water tends toward being soft and acidic.

They like areas that have a lot of dense vegetation, dark substrates, low light, and an open area they can swim around in.

You will need to purchase a tank big enough for a group of Harlequins, this is a fish that swims in schools so you should not just buy a single fish.

The minimum size of a tank for a very small group of Harlequin Rasboras is ten gallons. As this is a fish that is smaller in size, it doesn’t need a lot of room.

Fish keepers use a guide of two Harlequins for every gallon of water that the tank can hold.

This means that if your budget and home can handle it, you should purchase a larger tank (around 20-30 gallons) for more Harlequins and to give them more room for swimming in.

Creating the Landscape for Harlequin Rasbora

Harlequin Rasbora

When you are putting together the landscape of the tank, a goal should be to replicate the natural habitat of the Harlequin Rasboras. The closer you can match that habitat the happier and healthier they will be.

Harlequin Rasboras need live plants in their tanks. They also require open areas that they can easily swim around in.

For example, plants from the Cryptocoryne allow ample room for this if planted correctly. This plant is also a great choice because it comes from the waters that Harlequins are native to.

The substrate you pick is important because it is the base of the tank. The two types that are suggested are dark-colored sand or gravel.

This species of fish don’t spend too much time on the tank so there is little chance of them harming themselves from swimming against or into gravel.

After the substrate is picked and laid, it is ready for plants. The best plants for this species are dense plants with broad leaves like Cryptocoryne. Harlequin Rasboras enjoy plants because they can offer places to hide if they feel in danger.

Best Plants: Cryptocoryne, Aponogeton, and Cabomba
Best Lighting: Low light
Best Decorations: Driftwood, dark colored sand or gravel substrate
Decorations to Avoid: Anything sharp or jagged

Physiological Considerations for Harlequin Rasbora

Size: Up to 2 inches
Lifespan: 5-8 years
Temperament: Peaceful
Preferred Tank Region: Middle to top
Scale Thickness: Nothing of note.
Gill Considerations: Nothing of note.
Swimbladder Considerations: Nothing of note.
Fin Shape Considerations: Nothing of note.

With proper care and good genetics, the average lifespan of a Harlequin Rasbora can be upwards of five to eight years. On average they will live at least six years.

Compared to other species of fish, Harlequin Rasboras have significant variance in potential life spans.

However, a key to making sure these fish lives to their full potential is quality of life. By making sure they have quality food and that their tank water stays high quality, this will go a long way to ensuring they have long and happy fishy lives.

The male and female of this fish species have a noticeable difference in their markings. Normally the patch will be larger on the male fish, as well as rounded at the bottom of the triangle.

Unlike most with most fish, the female of this species is larger than the male.

Harlequin Rasboras are known for their vivid appearances. Their name of Harlequin Rasboras comes from the bold patch of black that is on their bodies.

The black patch contrasts with the other color of the fish and is part of why this species stands out so much. All the fish of this species has a wedge-shaped marking on them.

The color and shape are reminiscent of the triangle patterns that would be on old jester costumes.

The fish is a diamond shape that has girth in the middle of its body. Their heads and backends both taper to smaller points. The tail has an exaggerated taper that accents the tail.

Their coloring is orange or distinct light pink. Their exact shades will vary from fish to fish. Depending on water conditions the colors can change. The primary color of the fish covers most of its body, including the head.

The colors are mostly on the top of their bodies with light white on their bellies. Their colorings will sometimes also be found on their fins, often their dorsal and caudal fins are even more vivid than the colors on their bodies.

Society for Harlequin Rasbora

Harlequin Rasbora

While Rasboras are often kept separated in a species tank, they can be placed in a tank with other fish. They are known for being a peaceful species that enjoy tank mates of fish species that are around their size.

Author note: They are not known to nip on the tails of other fish or show any regular signs of aggression, if anything, they are more likely to be targeted by the aggression from another fish.

The way this species survives in the wild is through sheer numbers. This schooling fish grows up with and spends their time playing and exploring with a large group of other Rasboras throughout their lives.

In nature, it is rare for one fish to stray off by itself.

This community fish or shoaling fish must have other fish around it. If it spends long periods alone it will feel anxiety and hide.

Top Tip: Your priority should be to make sure to keep around eight to ten Rasboras together before thinking of introducing other fish species.

As numerous fish species can fit in well with Rasboras. Here are just a few examples of fish you can choose from: other types of rasboras, tetras, Gouramis, pentazocine barbs, guppies, and celestial danios.

If you are interested in having fish that occupy various levels of the tank, there are some bottom-dwelling fish that works great with this species.

Some bottom-dwellers that work include Corydoras catfish, kuhli, Otocinclus, and small loaches that are also peaceful.

Bear in mind that while we do our best to make sure our information is correct it is important to always consult with your local aquarium expert before you purchase anything from them and introduce new fishes into your aquarium.

Gender, Breeding, and Reproductive Considerations for Harlequin Rasbora

Breeding Harlequin Rasboras can be challenging.  They are known for being one of the more difficult tropical freshwater species to breed. However, with the right knowledge, preparations, and a special setup breeding tank, it can be done.

Due to this fish always wanting to live in schools of fish, it can be hard to separate them by gender.

Learning to separate them by gender can be difficult but there are a few ways to be able to tell the difference between the male and female of this fish species.

The male of the species is normally slenderer than the female and has a rounded edge at the back of the fish. This is also a rare fish species where the male is noticeably smaller than the female.

Females stand out because they are larger than their male counterparts. The black wedge found on this fish is perfectly straight on the female.

When you are ready to start the process, pick the fish that you want to breed and begin to feed them live food. Live food is essential because it provides the fish with a surplus of nutrition that they will need for breeding.

Top Tip: Live foods recommended by breeders include mosquito larvae and daphnia.

Harlequin Rasboras are unique from other rasboras in that Harlequins will lay their eggs rather than be scattering spawners. This species can be spawned in groups and it is suggested to have two males for every one female.

The water chemistry parameters need to have a hardness no higher than 4 dGH and a pH of around 6.4.  The water temperature needs to be maintained between 76 and 80 degrees F.

Adding broad-leaf plants to the tank is necessary because the fish utilize them during the process. The fish to be bred need to be placed the night before because breeding happens in the morning.

After the fish are done breeding, they need to be removed otherwise they will eat the hatched fry.

Nutritional Needs of Harlequin Rasbora

fish in tank

Harlequin Rasboras are omnivores that are truly equal opportunity eaters.

In nature this fish will go after small insect larvae, eggs, and plant matter, this means almost anything put into your tank will look like food to them. While this species of fish is ready to accept any kind of food, they prefer live food.

If feeding this species live food is not an option, frozen food, freeze dried, and flake foods will work as well. Daphnia, brine shrimp, and most worms can all act as great foods for supplementing this fish’s diet.

One of the most key parts of having your Harlequin Rasboras remain healthy for life is to make sure they have a varied diet.

Top Tip: By rotating what foods, you feed them it will help ensure they will not encounter digestive issues or become susceptible to certain diseases.

A problem with feeding Harlequins are that they have small mouths. This can prevent the fish from being able to eat some of the more common fish foods, so the smaller the food the better.

Many fish owners get around this problem by using tiny pellets or flake foods to act as a foundation of their diet.

Best Sustenance Food Type: Store-bought flakes and pellets, supplemented with live food.
Additional Food For Optimal Health: Insect larvae, Daphnia, Bloodworms
Special Foods and Considerations for Best Coloration and Growth: Live foods, infusoria for fry
When and How Often to Feed Fish Based on Life Cycle: Feed this species twice a day, giving only what can be eaten in two minutes.

Common Diseases and How to Avoid and Treat Them

One advantage of the Harlequin Rasbora is that they rarely get sick. They do not have any species-specific ailment. Keep in mind that without proper care the Harlequin can get sick just like any other fish.

There is a possibility that they can be infected by any freshwater fish disease.

Dropsy in Harlequin Rasbora

Dropsy, (also called edema, ascites, or bloat) is a swelling of soft tissues in the body by accumulated water and fluids. A quite commonplace this takes place in fish is the abdomen.

When a fish suffers from this their belly will noticeably drop down and it may develop lesions on its skin.

When a fish suffers from this disease it is caused by a bacterial infection after the fish has already had a weakened immune system.

By cleaning the water, feeding your fish nutritionally balanced food, and keeping them low stress, it is very unlikely they will get sick.

If you act quickly, the fish can be saved. The infected fish needs to be moved to a hospital tank. This tank’s water needs one teaspoon of salt per gallon of water.

Give the fish fresh and high-quality food along with antibiotics. Daily test the tank water to make sure it is at the right levels.

Ich in Harlequin Rasbora

Ich is a disease caused by a parasite. It is like a skin infection in humans, but is fatal to any fish that is being stressed out by poor food, bad water in the tank, or a tank that isn’t set up properly.

It is easy to spot because the fish develops small white spots that look like sand. The fish will start to scratch against any rock surfaces and gravel to relieve their pain.

As the disease advances the fish becomes lethargic with redness on their body and bloody streaks surrounding the fish.

As this is a parasite that moves from fish to fish, it is important to start and continue a treatment cycle that lasts for at least 10-14 days.

It is important to change the water frequently, discontinue carbon filtration and add medicine to the water to kill the parasite and help the fish heal.

Fin Rot in Harlequin Rasbora

Fin rot is a condition caused by a variety of bacteria. It is easy to prevent by always keeping high quality water in your tank, but hard to cure after it’s infected a fish. The more advanced the disease is, the less likely a fish will survive.

The disease first presents in the edge of fins start to discolor, then fraying, and pieces begin to fall off. Bloody patches appear as the bacteria eats at the fish.

This disease is caused by a combination of poor water quality and low temperature water. Overcrowded tanks, poor and outdated foods, and overfeeding can all contribute to this.

Treatment involves both using antibiotics and aggressively changing the water and checking multiple times a day to make sure the water quality is being maintained.

Best Antibiotics: Consult with a licensed veterinarian.
Treatments to Avoid: Adding too much salt to the tank for certain conditions.
Food Recommendations When Sick:Live food that the fish can easily eat.
Hospital Tank or Isolation Withing the Community Tank: They should always be isolated in hospital tanks to help them heal and prevent the spread of disease.

4 Facts About Harlequin Rasbora

Rasbora heteromorpha aquarium fish on a background of green plants
  1. Rasboras are a hardy fish, meaning they are excellent beginner hobbyist dreams.
  2. Harlequin rasboras are super easy going and fun to watch. They’ll peacefully dwell with some fish that notoriously don’t do well with others, like betta fish.
  3. Harlequin rasboras are schooling fish, so they do best in groups of six or more. Ideally, you’ll keep more of them together, though, as small schools stress them out.
  4. Harlequin rasboras are energetic little fish, but they’re pretty timid around humans and might take a while to warm up to seeing you hanging around their tank.

FAQs on Harlequin Rasbora

What tank mates should Harlequin Rasboras have?

Harlequin Rasboras are known to be shoaling fish. Ideally, you would want a school of this species with a minimum of eight, ideally, ten or more, depending on how big your tank is.

As for choosing other fish to house with your Harlequin, there are many options. As long as other fish are not too much bigger or prone to predatory behavior, then most other fish work great.

Examples of ideal tank mates include dwarf gouramis, cardinal tetras, danios, bettas, small rasboras, and cory catfish.

How many Harlequins can safely fit inside one tank?

The number of Harlequin you can safely put inside a tank depends on the size of the tank itself. While it is possible to keep a Harlequin per one gallon of water your tank has, it never hurts to give your fish more swimming and breathing room.

This fish species is very much a schooling fish species, so buying a single one is a terrible idea. Ideally, you should keep a minimum of ten in a twenty-gallon tank, but it doesn’t hurt to buy more fish and put them in a bigger tank.

Are Live Plants Safe to Place in a Tank with Rasboras?

Harlequin Rasboras do well with having live plants in their tanks. They do not eat plants, and if you desire to breed them, it’s vital to have plants in their tank.

Live plants allow your fish to have a safe place to hide if needed. Another benefit of live plants is that they help remove nitrates from the tank water and support all the fish safe and clean.

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