Harlequin Rasbora: The Complete Guide

Shoaling fish are very popular for home aquariums because of their fun group behaviors and striking colors. Harlequin Rasboras are a great example of an easy shoaling fish to add to your tank.

They are a striking fish which, when added as part of a group, will add a vibrant splash of color to your tank.

This captivating small fish has very few specific care needs and they aren’t very demanding. They’re easy to care for, and as long as they’re fed a simple diet, and their tank is kept clean, they’ll thrive. The perfect match for a beginner.

Keep reading to learn how to care for this fish including tank setup, breeding, what to feed them and much more…

Category Rating
Care Level: Easy
Temperament: Peaceful
Color Form: Silver Body with a Black Patch and Orange Fins
Lifespan: 5-8 Years
Size: Up to 2 inches
Diet: Omnivorous
Family: Cyprinidae
Minimum Tank Size: 10 Gallons
Tank Set-Up: Freshwater with Plants and Open Swimming Space
Compatibility: Peaceful Community Aquarium

Overview

Harlequin Rasbora
Credit: Wiki Commons, Author: Mariusz Dabrowski

The harlequin rasbora (Trigonostigma heteromorpha) is a tropical fish from the Cyprinidae family. Often referred to as harlequins, they are one of the most popular rasbora species for home aquariums.

This species is native to Asia and is commonly seen around Malaysia, Singapore and Thailand. Here they inhabit rivers, streams and swamp forests which resemble the blackwater habitats of South America.

These small shoaling fish are easy to care for, so you shouldn’t have many problems. They can be looked after by people of experience levels.

This makes them perfect for beginners starting a community aquarium. A small group adds some color and shoaling behaviors to the middle levels of the tank.

They’re peaceful so get on well with other peaceful fish, but they can become a snack for larger species.

You won’t struggle to find harlequins; they’re usually in high demand so most aquarium stores will stock them. You should expect to pay $2-4 per fish.

Typical Behavior

They are peaceful creatures; they won’t harass any of their tank mates. If anything, they are more likely to be the victims and will become stressed by boisterous fish.

Most of their time will be spent in the middle layers of the water, rarely journeying to the surface or substrate. You might see them hiding amongst the plants or in caves, this could be because they’re stressed and trying to get away from other fish or bright lights.

When you have a group, you’ll see some shoaling behaviors. The harlequins will move around together, sometimes displaying some interesting behaviors. On their own they are quite shy, but when they form part of a group, they come alive and you’ll notice they are much happier and content.

The larger the group, the more impressive their movements and colors will be.

Appearance

Harlequin Rasbora Appearance

These rasboras rarely grow larger than 2 inches. Since they’re small you can comfortably fit quite a few in one tank.

Their body has a tall mid-section but narrows towards the mouth and forked caudal fin. The rear half of the body has a black patch that narrows with the body and stops at the caudal fin.

This black patch is what gives this fish it’s name, being similar to the black patterns found on a classic harlequin outfit.

The rest of the body is silver, with tinges of orange. The fins are a darker orange but can vary in color intensity. This depends on lots of factors such as the conditions of the tank, stress levels of the fish and the population they were bred from.

While these designs aren’t striking on their own, a group can create quite a spectacle. This is the same for other fish too, like neon tetras.

Spotting the difference between males and females can be difficult. Males tend to have slightly larger black patches and a more rounded section where the anal fin attaches.

Habitat and Tank Conditions

Harlequin Rasbora Tank Conditions
Credit: Wiki Commons, Billyhill

In the wild a harlequin rasbora’s habitat can vary from rivers, all the way to peat swamp forests. Though conditions will differ between these habitats, there are a few things that are constant.

The waters in these areas are tropical so temperatures will be fairly warm and the pH will be near neutral (these fish won’t survive in extreme acidity or alkalinity).

Swamp forests will have waterlogged soil substrates, whereas rivers are more sandy. Planted in the substrate would be plants surrounded by rocks and debris.

Water flow is usually quite slow.

Tank Setup

Harlequins bred for aquariums are grown in environments based on their river habitats, so this is the habitat you need to recreate in your tank.

Start with a soft sandy substrate at the bottom of the tank. You could use gravel instead; this choice is not that important because they will rarely stray down to the bottom of the tank.

Place some plants around the tank for them to hide in, though leave plenty of open swimming areas for them to shoal and swim around in. Any rocks or decorations you add will be purely aesthetical for these fish; they’ll spend most of their time in open water.

You don’t need any specialist equipment; the filter outlet creates a strong enough current and most commonly sold aquarium lights are suitable. You just need to add a heater.

Set your heater between 72-81°F. pH should be 6-7.8 and keep hardness to 2-15 KH.

What Size Aquarium Do They Need?

Harlequin rasboras need at least a 10 gallon aquarium. Any smaller and there would not be enough space to shoal so you’d have to keep them in pairs or on their own.

How Many Can Be Kept Per Gallon?

Aim for around two per gallon. The larger the tank, the more you can get, and the more impressive a shoal’s display will be.

Harlequin Rasbora Tank Mates

Harlequin Rasbora Tank Mates

Harlequin rasboras are peaceful fish and will stay out of everyone else’s way. This means you’re free to pick other similar fish to keep as tank mates.

You should avoid most species that are larger than double the harlequin’s size as they will probably view them as a snack. Cichlids are likely to do this, especially the larger ones.

Boisterous fish can be a problem too. This species is quite timid so may become stressed if they’re chased by overactive fish. Clown Loaches and Bettas are a couple of species that may harass others.

Small peaceful fish are ideal. Cherry Barbs, Corydoras Catfish, Danios, Dwarf Gourami, Guppies, Hatchetfish, Mollies, Platies, Tetras and Zebra loaches are just a few good options. Aquarium invertebrates are growing in popularity all the time. You can keep snails and shrimp with harlequin; they’re unlikely to notice each other.

Keeping Harlequin Rasboras Together

You can keep harlequins together; in fact you should keep them in groups of at least four. They’re a shoaling species so do well in the company of their own kind.

The larger the group, the better their displays will be. Only keep an amount that can comfortably fit in your tank though, around two per gallon in at least a 10 gallon tank.

What To Feed Them

As omnivores, these fish will eat a wide range of foods. The main thing to watch out for is the size of the food. Harlequin rasboras have small mouths, so they’ll only be able to eat small particles.

In the wild this means they’re restricted to foods like plant detritus, small insect larvae and eggs. Their omnivorous diet means they are opportunistic; they eat whatever comes their way.

The easiest way to cater for their needs in an aquarium is through store-bought foods. At feeding times they will become active and happily take flakes or pellets from the surface. These have been specially designed to contain a range of nutrients.

It’s always best to vary their diet, if not for nutritional purposes, then just to keep it interesting for them.

This can be done with live or frozen foods. Daphnia, bloodworms, and insect larvae are some small examples. Live foods in particular make feeding times interesting by introducing movement.

Even though they can eat plants, it’s unlikely so you don’t need to worry about damage. This does mean you can feed them green vegetables though, or even use these to make your own homemade fish foods.

Feed them twice a day, only giving them what they can finish in a couple of minutes. This is easier on their digestive system, than giving it to them all in one go.

Remove any excess food from the tank after eating time to prevent decay.

How to Care for Harlequin Rasboras

Harlequin Rasbora Care

Harlequins are hardy fish, so they don’t get ill very often. With proper care you’re unlikely to experience any problems.

The most common diseases affecting them are issues for many other aquarium fish too. These include dropsy (fluid buildup causing swelling), Ich (White spots over the body), and fin rot.

These diseases, as well as many others, thrive in poor quality water. A dirty tank is one of the leading causes of disease outbreaks.

Therefore, cleaning your tank is a simple preventative measure to make sure you don’t lose your fish. After cleaning the tank, you might see an improvement in your fish. If not, there are treatments you can buy to help get rid of the disease.

Another factor that raises the likelihood of disease is poor nutrition. If a fish isn’t getting all the nutrients they need from their diet, they will be too weak to fight off disease.

Make sure your harlequins are getting a varied diet containing the foods we mentioned earlier. This should give your fish everything they need to stay strong.

If you keep them healthy, they can live for 5-8 years.

Breeding Harlequin Rasboras

Unfortunately they are one of the harder species to breed in an aquarium, but it is possible. They need to be kept healthy and the conditions in the tank need to match what they’d be used to in the wild.

A slightly warmer temperature (around 80°F) will help to encourage spawning. Your fish will need nutritional foods full of protein too; daphnia and bloodworms are good options.

Keep two females for every male. These males will perform a display to entice the female to mate.

You’ll need some broad-leaved plants (such as Anubias Nana) in your tank because once ready to spawn, the female rubs her belly on the underside of a leaf to signal the male. The male will come to fertilize the eggs. These will be attached to the leaf and hatch after 24 hours or so.

Separate the parents from the fry as they will try to eat them. The fry will be nearly completely clear and feed on a yolk sac for the next 24 hours.

After this, you will have to start feeding them. Newly hatched brine shrimp are one of the few foods small enough to give them. A poor diet can affect development.

Is the Harlequin Rasbora Suitable for Your Aquarium? (Summary)

These fish are peaceful tank mates, so they do well in most tanks.

A small arrangement of plants is all you need to keep these fish happy.

If you’re looking to breed them then they will need much more attention. Conditions need to be perfect or else they won’t start to spawn.

Add these fish to your tank and you will be rewarded with unique shoaling behaviors and strong colors. The more you’re able to fit in the tank, the more impressive these displays will be. A large group could compete with some of the most attractive fish in the aquarium industry.

Do you have a group of these shoaling fish? Let us know your experiences in the comments section below…

Robert Woods Portrait
Robert Woods is the creator of FishKeeping World, a third generation fish keeper and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America and the Nature Conservancy.

7 Comments

    • Hi Jas, given that both of those species like to be kept in small groups, a 10 gallon tank is too small. You can keep 3 or 4 Guppies, or 2 – 3 Rasboras in a 10 gallon, depending on which species you’d like. Thanks, Robert

  1. Hi I was wondering and it is probably a stupid question but I’ll ask it anyways would I be able to put these fish in a five gallon?

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