Harlequin Rasbora Care – A Complete Guide

Thank you for visiting! By the way… any links on this page that lead to products on Amazon and other stores/partners are affiliate links Aquarium Store Depot earns a commission if you make a purchase.

As an extremely vibrant shoaling fish, the harlequin rasbora has garnered quite a big fanbase for itself. Every fish hobbyist wants it. The fish is of a peaceful yet cheery disposition. As it swims through the water, its metallic body catches the light and glistens like a dream.

If you feel an intense liking towards this fish, join the club. But hey, don’t take any quick decisions yet. Before you decide to get one for yourself, learn thoroughly about Harlequin Rasbora’s care. These fish aren’t difficult to care for, but you need to be very meticulous with them. 

The last thing you’d want is for this beautiful fish to die on your watch. But thankfully, you’re here. So it will never come to that. 

In this article, we will give you all the information on Harlequin Rasbora so that you can take care of them properly.    

Species Of Overview

Scientific NameTrigonostigma heteromorpha
Common NamesHarlequin Rasbora, lamb chop rasbora
OriginSouth and Southeast Asia
DietOmnivore (they aren’t picky eaters)
Care LevelEasy to Care For
ActivityCalm, friendly and active 
Lifespan5 to 8 years 
Tank LevelMidwater
Minimum Tank Size10 gallons
Temperature Range71 ° to 80 °F
Water Hardness6 to 8 dkH
pH Range6.0 to 7.8, with 6.5 being the optimum 
Filtration/Water FlowModerate
Water TypeFreshwater
BreedingEgg spawners
Difficulty to BreedVery Difficult to Breed
CompatibilityCommunity tanks
OK, for Planted Tanks?Yes

Everyone wants these colorful fish in their aquarium because of its cheerful disposition and glistening patterns. Fortunately, this is a beginner-level tropical fish so it isn’t too difficult to keep it healthy.

Behaviour: What to Expect 

The first principle of keeping this fish healthy is to understand its basic features and behavioral patterns.

Harlequin Rasboras are a peaceful fish. They aren’t wily creatures that will drive the other fish crazy around the aquarium. 

Depending on the company they are kept with, you will see the behavior of these fishes change accordingly. If you pair them with aggressive fish, they will become reclusive. They will find a corner in the aquarium and stay in hiding most of the time. These fishes become somewhat nervous around will exhibit boisterous energy. 

However, if you keep them with friendly company, they will flourish. These shoaling fish like to stay in the middle of the community tank with their gang when they feel safe. 

If they are found near the surface of the water or its substrate, there’s something wrong. 

Sometimes Rasbora becomes timid if new fish are introduced in the aquarium. So it would help if you kept an eye on them after introducing new fish in their tank. If your Rasboras don’t come out of hiding, then the new fish isn’t good company for them. However, there is nothing to worry about if they do come out of hiding. It’s natural for them to take their time before they trust the new fish.  

But don’t be reluctant about introducing new fish into their tank. If there are plenty of fish around to school with, Harlequins are at their best behavior. The more fish in the school, the better. 

If they are in a big school, you might see some of them nibbling at each other occasionally but that is nothing to be concerned about – this behavior is quite playful and typical from time to time. 

However, you might see one or two Rasboras become slightly aggressive is when they are spawning. The pregnant rasbora females need a secure place for their eggs, so that they might become vigilant towards other fish coming too close to their spawning area. 

However, this behavior is rare because it is generally tough to breed Rasboras in the first place. And in any case, if you want to breed Rasboras, transfer them into a separate breeding tank to increase chances of success. 

What Do They Look Like?

How Do Harlequin Rasboras Look Like

Harlequin rasboras look orange but that’s only a gradient on their silver body. The orange hue runs down from dorsal fins and fades away around the mid-region. A little bit of the orange gradient runs from its tail too, but just as well, it fades off beautifully into the rest of the colors. 

Their tall mid-section tapers near the mouth and the tail. In the rear part (abdominal region) of the Rasbora’s body, there is a dark black triangular patch characteristic of their uniqueness. 

Rasboras generally grow around 2 inches in length. They might grow to become slightly bigger than that if you are keeping them in ideal conditions and larger aquariums. 

One curious thing about them is that their fins change in hue depending on their tank’s conditions and mood. Their fins turn darker in color if their water is unclean or if they are under stress. And if the fish contracts any disease, their fins will always be the first part of their body to show signs on it. 

Male and female rasboras are similar in size and description. However, the black patch is slightly bigger on the male. Also, males seem to be a bit more orange than the females. The females have more of a golden hue on their entire bodies. And if you see that the belly of a female harlequin rasbora is turning bright, it means there are eggs in its little pouch. 

The appearance of the harlequin rasbora might not seem too extraordinary to you. Still, since you’re reading this article, we’ll assume that you have seen a school of harlequin rasbora swim together. 

Rasboras are shoaling fish that are at their best when they’re together with their bunch. When a school of harlequin rasboras swim together, the features of their body display cool colors and patterns by corresponding in a peculiar manner that is truly impressive to behold. 

Natural Habitat of Harlequins 

Harlequin rasbora (Trigonostigma Heteromorpha) are freshwater fish from tropical habitats like rivers, swamp forests, and streams. There are many variables involved here but water chemistry, tank water temperature, and pH value stay the same throughout all of these habitats. 

Swamps generally have soil substrates that are full of water, but riverbeds are pretty sandy. So you see, there are quite some differences here. The common denominator in both these habitats are aquatic plants. Harlequins like plants very much; when they become timid, they hide behind plants to feel safe.  

Harlequin Rasbora Care Guide

These small freshwater fish are accustomed to living in shallow water with an abundance of plant life.

In their natural habitat, the pH of the water is pretty low. However, the harlequins that you will find in the market have been bred in higher pH. 

If you got your Rasboras from the store, ask them in which pH these fish were bred. Generally, commercially bred Rasbora stay healthiest if kept in a pH range of 6.8 to 7.8. 

The alkalinity of water should be around 6 to 8 dkH for store-bought Rasbora. If the alkalinity falls or drops, your fish will become weak due to an inability to get rid of metabolic wastes.  

The temperature of the water should be 71 to 80 degrees Farenheit. If the temperature goes above this level, oxygen solubility of the water will decrease and your fish will become lethargic.  

So the water plays the most critical role in keeping the fish healthy. . Make sure always to keep the water conditions at an optimum level. Here’s what you need to do.

Tank Size

You can keep harlequin rasboras in a 10-gallon tank. Bigger tanks are always better, because these are shoaling fish that don’t like to isolate or stay dormant. So whatever you do, make sure that you don’t go with anything smaller than 10 gallons. 

One rule of thumb is to get a pair of harlequin rasbora for every 2 gallons of water. That way, you get to keep 10 in a 10-gallon tank.

However, we would strongly suggest you get a bigger tank because the fish will thrive better in a bigger space where they can swim more freely. 

Tank Preparation

This is the main deal. If you get a decent tank but set it up incorrectly, the health of your Rasbora will still keep deteriorating. 

Make A Substrate: Create a soft substrate at the bottom of the tank. Use soil, sand, or gravel to mimic the riverbed or the swampy substrates. 

The substrate is just to create the same atmosphere as the fish had in their natural habitat. These fish aren’t bottom-dwellers, so you’ll rarely see them poke around near the bottom but you still have to create a suitable habitat for them with the substrate. 

Add Plants: Put some nice, aquatic plants in the tank so that your harlequin rasbora can go into hiding if they feel stressed or threatened in any way. You can also add rocks and other ornamental artifacts in the aquarium to make the tank atmosphere aesthetically pleasing. 

Control Water Parameters: Use a heater to control the temperature of water against the changing temperatures outside. Stick a thermometer onto the tank and keep an eye on it to check the temperature of the water from time to time.  

Setting Up A Breeding Tank For the Harlequin Rasbora

It isn’t easy to breed a rasbora in a regular community tank at home because they need very specific conditions for successful fertilization to occur. 

You need to transfer the breedable Harlequins to a separate tank and create the perfect breeding conditions. 

Put soft water in the tank, aim to stay within 1.5 to 2.5 dkH of their preferred hardness of 7. The temperature should be 71 to 80 degrees Fahrenheit. Then put in their favorite plants – Cryptocoryne. This plant has broad leaves that are perfect for them to hide behind while they’re spawning. 

Keep the breeding tank in low light, because bright lights make Rasboras somewhat nervous.

If the tank conditions aren’t perfect, then the fish won’t be fully fertile. So learn how to make soft water and how to adjust the pH of water before you attempt this. 

For more information on the intricate details of the actual breeding process, watch this video from Mark’s Aquatics

Tank Mates 

Rasboras are schooling fish, so they like to swim around with a lot of tank mates. Don’t keep them on their own because they will become shy and reclusive. While they look to be around many types of fish, you still will need to be meticulous when choosing their company. It will help if they are kept in the company of fish with which they can be cheerful and active but never fall prey.

Good Tank Mates

The good news is that plenty of magnificently colored peace-loving fish can be kept with schools of Harlequin Rasboras. Here are just a few fish and inverts that work well: 

Bad Tank Mates

Any fish that is twice the size of your Harlequin Rasboras shouldn’t be kept in the same tank with it. They say it’s better to be safe than sorry. So you should keep your fish safe in the tank to avoid feeling stressed out about them during the day. Some of the fish that you should definitely avoid are:

Note: Some Betta fish lovers will argue that Betta fish is too slow a swimmer to ever harm the Harlequin Rasbora. However, this can still be a mixed bag. For one, a school of Rasbora can feed quickly and leave a Betta with very little to eat. There are also more athletic Bettas like Plakats that can potentially harass your Rasbora school. The Betta and the Rasbora will likely come close if they live in a tank together – especially if the tank is small. So if you want to protect your rasboras, we suggest you to not take chances with a Betta fish. 

What Do They Eat?

Thankfully, harlequin rasboras aren’t fussy eaters. They are omnivorous, so they will eat pretty much anything starting with zooplankton, worms, crustaceans, and small insects that are edible. All you have to do is make sure that the food isn’t toxic for them. 

Since you want your rasboras to be healthy, take some out to condition them to a healthy, all-inclusive harlequin rasbora diet by introducing a variety of foods to them in tiny amounts. Do note that they have tiny mouths, so it’s better to not give them anything that isn’t bite-sized. 

When they first come to live in your aquarium they will be a bit shy, so you need to draw them out by giving them proper foods. Start off with herbivore fish foods such as Algae Wafers and Spirulina. Give them good quality fish food, a range of greens like blanched spinach, water lettuce, and then slowly introduce them to live food and frozen food. A good staple food to try is Xtreme Aquatics Nano formula

Great For Nano Fish
Xtreme Aquatic Foods Nano

Xtreme Aquatics Nano formula is specially designed for smaller fish and contained a well balance mix of raw ingredients. It is a great staple food for your nano fish.

Buy On Amazon

Rasboras are particularly found of Daphnia, shrimp, blackworms, and bloodworms. They will eat these meaty options live and frozen. When you give them live food, they will become overly enthusiastic and chase it around for a bit before eating it – it’s quite adorable to watch, really. 

Diseases That Affect The Rasboras

Rasboras are hardy fish from the streams, rivers and swamps, so they don’t get sick easily. Here are some of the diseases that might inflict suffering on your beloved fish. 

Fungal Infections

This is the most common disease that Harlequin Rasboras get. If left untreated it starts to damage vital organs like liver, brain, lungs, etc. 

Cause: Ichthyosporidium, Exophiala sp., and Flavobacterium columnare

Signs: Patches on the gills and skin, slimy layer on the surface of their skin, and skin turning brown.

Treatment: Isolate the infected fish from its tank mates, add aquarium salt in water, get rid of chlorine from the tank water, increase the water temperature to 77 Fahrenheit, and try an over the counter medication like API Fungus Cure.

Ich/White Spot Disease  

This persistent disease is another widespread one for rasboras. External parasites will cling onto the fish’s body and cause white spots to appear on its skin and gills.

Cause: Ichthyophthirius Multifiliis (an Ectoparasite), contact with other infected fish, sudden shifts in the water temperature of the aquarium, decorative plants that have parasitic cysts on them.     

Signs: Crystals formation on the body, skin becoming slimy, asthmatic breathing, itching against rough surfaces, and hiding for days on end.    

Treatment: Bring the water temperature up to 71.8 to 86 degrees Fahrenheit, or try an over the counter medication like Ich-X


This disease is highly contagious, but it only affects freshwater fish. 

Cause: Low oxygen levels in the tank, and temperature of 80 Fahrenheit degrees.

Signs: Ulcerations on the skin, visible accumulation of mucus in its gills, and dorsal fin, noticeably long periods of time gone without eating.  

Treatment: Stabilize the water temperature, and consult the vet for antibiotics or try an antibiotic like API’s Furan-2


This is basically kidney failure. Water and other fluids accumulate in the body and cause swelling in the abdomen. 

Cause: Aeromonas bacteria, water with excess ammonia and nitrites

Signs: Irregular swimming, gills losing color, scales standing out, stringy faeces, and bloating belly. 

Treatment: See the freshwater disease link posted above.

Fin and Tail Rotting 

The tissues of the tail and fins start rotting outwards in. The rotting might start from a wound that your fish already has, and it also may happen because of unclean water. 

Cause: Dirty water, overfeeding, low-nutrition food, and high levels of stress. 

Signs: It starts with inflammation of the fins. Then the fins start to lose color and eventually start becoming very fragile. 

Treatment: Clean the water, optimize the temperature and pH of the water in the tank. Use a medication like SeaChem KanaPlex.


To watch your Harlequin Rasboras live their best life, make sure you keep them with friendly tank mates. Remember to give them proper sustenance, remove any excess leftover from their waters, and do remember to clean the entire tank every 2 to 3 weeks. May your beautiful Harlequin Rasboras live long and keep many more of your guests in awe! 

We hope you didn’t have any trouble following our instructions about proper Harlequin Rasbora care. With a little bit of mindfulness, you can keep your fish very active and healthy. Best of luck! 

Meta: Learn Harlequin Rasbora care, and give your beautiful rasboras their best life.

Leave a Comment


9 Types Of Geophagus (With Pictures)
Cichlids are some of the most popular freshwater fish families in the aquarium trade, famous for their bold markings and colors, interesting behavior, and vibrant personalities. While many species have a reputation for aggression, one group of cichlids, the 'earth eaters' are known for their relatively peaceful temperament and amazing colors.
The 7 Best Plants For Cichlid Tank (That They Won't Eat)
Cichlids are aggressive towards each other, but are they aggressive to live plants? Most Central and South American cichlids can be kept with a variety of aquarium plants, but African species are more challenging to pair due to water parameters. It's not impossible though!
Why Angelfish And Guppies Are A Deadly Combo
You might think that guppies are easy fish that can be kept with nearly any other species, right? While these small, hardy fish can get along with most fish species, they are not compatible with angelfish. Keep in mind that angelfish are a type of cichlid, and so they should be treated as such.