harlequin rasboras

Harlequin Rasboras: A Complete Guide

Harlequin rasbora a majestic and wonderful addition to your home aquarium. This beautiful, attractive small fish can grab anyone’s attention within a second.  This is a schooling fish and a large group of these beauties can cheer up your aquarium at once.

It is metallic vibrant in color and is quite easy to take care of. Harlequin rasboras are peaceful and entertaining.  To keep this amazing fish at your home you just have to follow certain tips.

Let’s not wait anymore get started with this wondrous creature.

All About Harlequin Rasbora


Harlequin rasbora one of the most popular tropical freshwater fish, they are most frequently named as a harlequin. These rasboras belong to a Cyprinidae family.

SpecieT. heteromorpha
Scientific nameTrigonostigmaheteromorpha

Harlequin rasbora lives in freshwater, rivers and streams. They locally inhabit the swamp forests resembling the blackwater habitats of South America. These swamps usually have a very small amount of minerals and high amount of humic acids.


This interesting fish originally belongs to Asia and is also seen around Malaysia, Singapore and Thailand. Harlequin rasbora was first found in the early 1900s. Within a short time, this fish gained fame as being the favourite freshwater fish.

It was first classified in genus Rasboras but regarding their different shape, they are called heteromorpha. Moreover, they are named harlequin, based on their black triangular patch on the rear part of their body.


This is an incredibly small and amazing freshwater fish. Out of more than five dozen species of rasboras, this harlequin specie is most popular among the aquatics. They hardly grow more than 2 inches in size. A smaller tank can easily fit 5-6 of them.

Harlequin rasboras have an amazing body shape, being tapered at both ends and wide at the mid-section. Their caudal fin is fork-shaped. They have beautiful and mesmerizing patterns. At the rear portion of their body, they have a nice black triangular patch ending near the caudal fin. This dark portion is characteristics of harlequins.

Rest of the body is sparkling silver in color with stripes of orange-red color. Their fins are dark orange. This wonderful combination of orange, silver and black makes them quite fascinating. Their color intensity varies with their habitat, their diet and water conditions they face.  


There are many different types of harlequin rasboras available, all credit goes to cross-breeding these days. Based on their colors there are following different types.

  • Purple harlequin rasbora
  • Black harlequin rasbora
  • Pale harlequin rasbora
  • Red harlequin rasbora
  • Blue harlequin rasbora
  • Copper harlequin rasbora

Aquarium guide

Keeping a bunch of harlequin rasboras in the home aquarium is way too much easy. As they are easy to take care of, require very little tank space, they are friendly and peaceful and above all their diet is quite simple.

There are just a couple of things you should keep in mind before buying one of them.

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Tank size

As they are small, they require very little tank space. The basic requirement is 10 gallon per fish. It means if you are keeping a bunch of these little fairies a 50-60 gallons tank is a lot of space. Harlequin rasbora is a schooling fish and gets along well with other fish.

Water parameters

As harlequin rasboras are freshwater fish so providing the nearly same environment is necessary for their survival and growth.

Temperature72-81-degree Fahrenheit
Water hardness2-15 KH
Tank size10 gallons
Ammonia0 ppm
Nitrate and nitrite0 ppm
Tank levelTop and middle dwellers

When it comes to setting up an aquarium for your harlequin rasboras start by selecting a soft substrate, gravel, as well as sand, can both be good options. Although the choice of the substrate does not matter much as rasboras are not bottom dwellers, so they hardly get near the bottom.

After setting up the substrate well choose your favourite plants or small rocks. Harlequins are remarkably active and they will love to play around so try to put some caves or stuff like that. In the case of live plants, Cryptocoryne is an amazing choice.

Small-sized aquarium filter can do best in case of harlequins. Moreover, the water pump won’t be necessary as the filter currents will be enough.

A water heater is fairly needed in case of rasboras. To maintain a temperature of 72-81 degrees a small water heater will do good. Nice, warm water is perfect for the growth and maintenance of their colors.

Cleaning and cycling the tank

For keeping the water fresh and clean change almost 10-15% of the water every week. Begin with cycling the tank almost a week before putting the fish in. Don’t use tap water as it is contaminated. For maintaining accurate water parameters use water testing kits once a week.

Growth rate

Although, harlequin rasboras are fairly small in size but they grow astonishingly fast. Depending upon their diet and water environment they can even become adults in just a short span of 3 months.

As they reach a maximum of 2 inches in size thus this fast growth rate is quite a treat for fish keepers. Harlequins are pretty hardy and can survive changes in water parameters.

Life span

Being fairly good at the growth rate and hardy as well, harlequins can live for well a good amount of time. In most cases, harlequins can survive up to 5-8 years. Considering their small size this long-life span is positively surprising.

Although there has been no systematically organized data regarding their life span, still if harlequins not get eaten up or diseased, they can live up a nice span of life.


Harlequin rasboras are very popular among fish hobbyists because of their friendly and calm nature. In a natural habitat, they choose their friends on their own. While in captivity they still get well along with other fish.

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Their favourite tank mates are following.

  • Cherry barbs
  • Guppies
  • Mollies
  • Cory catfish
  • Gouramis
  • Platies
  • tetras
  • zebra loaches
  • hatchet fish

But there are certain fish that can make a good meal out of your harlequin so be aware of them they are following.

  • Cichlids
  • Oscars
  • Bettas
  • Arowana
  • Clown loaches

Rasboras are tiny and delicate so they easily get stressed out when large fish start chasing them. Therefore, avoid keeping rasboras with any larger fish type.

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Harlequin Rasbora Food

Harlequin rasboras are omnivores and eat anything that comes up their way. One thing that hinders their diet is their smallmouth. Because of their tiny might, they might die ingesting anything bigger. So, you should be careful while feeding them. Anything smaller than their mouth is well appreciated.

In a natural environment, rasboras feed on small insects, snail, worms, danios and larvae. Moreover, they can also eat parts of plants, skipping bigger leaves or harder parts.

In captivity, harlequins appreciate packaged food, as well as any form of dried or frozen food, flakes, fish pellets and bloodworms, are the best choices. To provide the necessary amount of protein, minerals and vitamins change of diet after some days is good.

Over-feeding can be a risk factor, therefore, rasboras should be fed twice a day. The quantity of food should not exceed the amount they can eat in almost 2 minutes. Altogether, rasboras are pretty easy going when it comes to their diet.

Differences Between Male and Female Harlequin Rasbora

Differentiating harlequin rasboras is pretty easy. Although, rasboras have pretty much the same size and color there are certain differences as well.

Firstly, the males have more intense red color around their dorsal and caudal fins. Females generally have more golden hue to their bodies. Unlike other fish, the male rasboras have ore pigments and are more vibrant in color.

Besides, to that, a male is slenderer and slimmer in appearance as compared to females. Female harlequin rasboras are chubbier looking and healthy. The female has deeper belly shape as compared to their other partner.

Lastly, males have a rather round edge at the end of their triangular black patch. In comparison, the female has a straight line at the edge of the black patch. This pattern in ale is their characteristics and it makes sexing in harlequin rasboras quite easy.


When it comes to breeding the harlequin rasboras could prove to be a little troublesome. Unlike other species of rasboras, the harlequins are egg layers. We will explain it later.

In an attempt to breed the harlequin rasbora start by building an aquarium. A 30-40-gallon tank will do the job. Water parameters will be following.

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Temperature76-80-degree Fahrenheit
water hardness4 dGH

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Process Of breeding Harlequin Rasbora

The above-mentioned conditions are beneficial for successful breeding to occur. Start by adding two males and one female in the breeding tank. According to most experts, it is necessary as the female can find it natural. Moreover, it stimulates the male and female to advance and start breeding.

Within a span of 12-14 hours (night is preferred) the female is ready to lay an egg. Introduce some plants in the tank, as the leaves are their favourite spot for laying eggs. After some time, the female will to the leave and the male will entertain as well as protect her by dancing and trembling movements.

Male usually rub their bodies against their partners to encourage them. Female harlequin rasbora can generally lay 12 eggs at a time. And within a period of 1-2 hour, they can lay almost 300 or more eggs. The eggs are laid in layers and on the leaf surface that’s why harlequins are known as egg-layers.

After completing the spawning remove the parents from the eggs and let the young ones hatch. In a short time of 24 hours, the young ones come out of their eggs. Then is the time to feed them. Try feeding them finely ground up food like infusoria etc. the harlequin can reach maturity in a period of 6-9 months.  

Giving accurate water conditions and necessary food during the growth period is a must for their health and survival. Brine shrimps and bloodworms are other good options to feed the young ones.


Although rasboras live a quite healthy life there is a number of common fish diseases that harlequins can face. most common ones are following.

  • Dropsy disease (swelling due to fluid accumulation)
  • Fin rot
  • Tail rot
  • Ich disease (white spot all over the body)

In order to protect your beloved fish from any disease or sickness remember the below-mentioned tips.

  • Change the water regularly.
  • Select the fish carefully.
  • The tank mates should be healthy.
  • Water parameters should be maintained.
  • Separate the sick fish ASAP.
  • Lastly, keep an eye on their diet as well.


Harlequin rasboras are remarkably calm and peaceful. They don’t mess with any other fish. Although they tend to get suppressed and are easily stressed by large fish. Harlequins are middle dwellers and they tend to get irritated by light and sound.

They are quite entertaining and active. Harlequins have an amazing ability to cheer up the whole aquarium with their moves and activities. They keep their owners happy by their impressive colors and exciting tricks.


Harlequins are best to be kept as a pet. They are delicate, intelligent, entertaining and friendly. In the beginning, they can be shy but after some time they get along well. The larger the school the more impressive they look.

I hope I have concluded every aspect of this amazing fish. Looking forward to your positive response.

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