How to take care of Harlequin rasboras fish?

We will talk about harlequin rasboras care in this blog post.We will also discuss important factors such as their habitat, types,lifespan, tank set-up, water parameters and healthcare,etc.Everything you need to know about harlequin rasboras care will be briefly discussed.


In this blog

  • Key specifications of harlequin rasboras
  • Why is harlequin rasboras care important?
  • How many harlequin rasboras should you start with as a newcomer?
  • Habitat of harlequin rasboras fish
  • Types of harlequin rasboras
  • Different strains or colors of harlequin rasboras
  • General and physical attributes of harlequin rasboras
  • Harlequin rasboras lifespan
  • Harlequin rasboras tank set-up
  • Harlequin rasboras diet and feeding requirements
  • Harlequin rasboras healthcare and health conditions
  • Harlequin rasboras daily care and bi-weekly care tips
  • Summary

How to take care of Harlequin rasboras fish?

Daily care tips for harlequins

  • Regularly clean the gravel using gravel siphon to remove leftovers from the tank.
  • Feed them twice a day.
  • Avoid overfeeding 
  • Observe them regularly to know if they are doing well or not.Separate sick rank mates to other tanks until they recover well.
  • Regularly monitor the water conditions.
  • Check all the tank equipment whether they are working or not.
  • Keep them away from direct sunlight.Give plants indirect sunlight for their growth and maintenance.

Bi-weekly care tips for harlequins

  • Change 15-20 % of water weekly and 50 % water monthly.
  • Weekly water testing is recommended to maintain stable water conditions in the tank.
  • Quarantine sick fish for several weeks in separate tanks to avoid the spread of disease to other tank mates.
  • Always quarantine live food for several weeks before feeding them to avoid parasitic infections.
  • Clean the tank plants and decors once a week mandatorily.
  • Trim tank plants religiously.Don’t allow them to overgrow.
  • It is recommended to clean the entire tank every 3 week.

Key specifications of harlequin rasbora fish

Scientific name Trigonostigma heteromorpha
HabitatConservation statusAsia (tropical fish)Least concern
Lifespan5-8 years
Body sizeBody shapeColorSpecial traitSexual dimorphism2 inches (5 cm)- fully grownSlender and plumpyReddish copper colorBlack wedge covering the backYes (especially when viewed from top of the tank)
Another namesRed rasboraHarlequin fish
Optimum temperatureOptimum pHWater hardness72F-81F6.0-7.82-15 dGH
TemperamentBeginner or experienced PeacefulPerfect beginner fish 
Care levelEasy 
Tank size and set-upTank type (Prefered)10 gallons (minimum)Planted community tank
Preferred plants/decorationsLive aquatic plants and floating plants
CompatibilityOther peaceful fish
No. of harlequin species found Three species, those are color variants.
BreedingIt is a bit difficult in tank settings.Breeding temperature- 82.4FEgg layer

Why is harlequin rasbora care important?

Harlequin rasboras are hardy species and easy to care for.Like any other aquarium fish they also need proper care from time to time for thriving in an artificial environment.If they are not given proper care and attention they will get infections which could weaken their immune system and make them inactive and unhealthy.

How many harlequin rasboras should you start with as a newcomer?

Rasboras are very beautiful and vibrant aquarium fish and getting just one of these enchanting personalities would not do justice to them.

They are shoaling fish and should be kept in groups of 6-8.They display such beautiful formation and colouration in tanks that no one can have just one of them.

Don’t get confused while buying harlequin rasboras as they look similar to Lambchop rasboras aka Pseudo Harlequin rasbora.They both have somewhat same colouration.

Habitat of harlequin rasbora

  • Native – Asia
  • Distribution- Freshwaters of Thailand, Singapore and Malaysia
  • Water type- Acidic black water 

Types of harlequin rasbora

  • Black harlequin rasbora
  • Blue harlequin rasbora
  • Gold harlequin rasbora

Different strains or colors of harlequin rasbora

Different colors variations in harlequin rasboras are:

  • Black 
  • Blue
  • Gold 

General and physical attributes of harlequin rasbora

Male harlequin rasbora:

  • Slender shaped body 
  • Patch-straight
  • Smaller in size 
  • Redness – darker than females
  • Semi -aggressive

Female harlequin rasbora:

  • Plumpy body
  • Patch-rounded
  • Large in size
  • Lighter than males
  • Peaceful

Harlequin rasboras lifespan

Harlequin rasboras can live between 5-8 years depending upon the right tank size, nutritional diets,ideal vital parameters, suitable tank mates and stress free environment.

Harlequin rasbora tank set-up

Tank sizeLight intensitySubstrate/decorationWater parametersTemperatureTank plantsTank mates

Tank size for harlequin rasbora

  • Minimum tank size – 10 gallons tank
  • Number of rasboras in 10 gallons tank- 6 rasboras can be kept.
  • Additions gallons- 2 rasboras per gallons
  • Community tank size of 20-30 gallons would be perfect as it provided lots of swimming and hiding space to them.
  • Tank size is directly proportional to their activity.

Harlequin rasboras shoal together in the middle layer of the tank.So provide open areas for swimming and schooling.

Don’t overcrowd the tank with too many rasboras, it can suffocate them and even hinder their natural growth.

Light intensity for harlequin rasbora

Harlequin rasboras don’t need bright lighting in their aquarium, because it might stress them out.A standard aquarium light will be sufficient for them.

Light intensity may vary if you are adding live plants to harlequin tanks because cryptocoryne and aponogeton species may need enormous lighting and cabomba prefers subdued lighting.They need sunlight for their maintenance for a few hours a day.  

Substrate/decoration for harlequin rasbora

Being a middle level dweller,they rarely go to the bottom of the tank but if you are keeping bottom dwellers with them then you can go ahead with dark sandy substrate or gravel for them.

Use aquarium gravel siphon to clean the gravels everyday.The gravels contains lots of uneaten food and detrtuis.It is very important to maintain the gravels by siphoning it out daily.

An uncleaned gravel could change the water chemistry and make it unstable for fish to survive by increasing the nitrogenous waste products in the tank.

Avoid sharp decorative items in the aquariums as it can hurt the fish.Always keep the tank clean by cleaning tank decorations weekly or monthly twice.

Water parameters for harlequin rasbora

They come from soft, acidic black waters of Asia, So it is important to replicate the same conditions in the aquarium settings too.

Water movement- They live in slow water currents in their natural habitats so maintain the same current in their tanks.Use filters with moderate flow rate for filtering out waste efficiently mechanically, biologically and chemically.

  • Water pH-6.0-7.8 (softer more acidic water)
  • Water hardness-2-15 dGH

Temperature for harlequin rasbora

It’s very important to maintain the right temperature in fish aquariums.

Fish metabolism is entirely dependent on stable temperatures and if there is a sudden dip in the tank temperatures then it can make them sluggish and weak.

Good thing about harlequin rasbora is they can tolerate temperature fluctuations but this doesn’t mean they can accept sudden dips in temperatures.

  • Aquarium heater is required in colder regions and to maintain temperature fluctuations.
  • Aquarium thermometer is also required to set the required temperature
  • Ideal temperature – 72F-81F
  • Breeding temperature- 82.4F

Tank plants for harlequin rasbora

Include dense live plants with broader leaves:

  • Cryptocoryne species-This species gives exact touch of their original habitat.
  • Aponogeton species
  • Cabomba gives bushy appearance
  • Arrange longer plants to the sides of the aquarium by leaving open space for swimming.

Tank mates for harlequin rasbora

Harlequin rasboras are famous for their peaceful temperament and friendly behaviour.They get along well with almost every aquarium fish.

But it’s very important to choose the right tank mates for them,because if they are kept with just anyone without knowing what could be the consequences then definitely it will be difficult for them to survive in a stress prone environment.

To provide them stress free environments avoid large,predatory fish and fin nippers.They can become food to large fish.

Suitable tank mates:

  • Other rasboras
  • Cardinal tetras
  • Small characins (neon tetras)
  • Bettas 
  • Cory catfish
  • Dwarf gouramis
  • Danios 
  • Assorted small barbs
  • Otocinclus 

Harlequin rasbora diet and feeding requirements

Harlequin rasboras accept all types of food but be careful with their mouth size, it’s quite small and it can fit anything of smaller size.Include lots of protein in their diet for keeping them healthy.

Feeding frequency- Harlequin should be fed twice a day, which they can finish in minutes.

Overfeeding should not be done because it can upset their digestion and secondly it can create lots of biological waste in the tank.Being a responsible aquarist it’s very important to remove all the uneaten food daily from the tanks to avoid ammonia spikes in the tank.This spikes can completely change the water chemistry and make it unstable for your fish to survive.

  • Commercial food-Micro pellets and flakes
  • Live and frozen food- Insect larva, daphnia, bloodworms,baby shrimps
  • Plant based food- They can be trained to eat fresh vegetables too.

Harlequin rasbora healthcare and health conditions

Harlequin rasboras are hardy species and can tolerate a wide range of water parameters.

But hardiness has nothing to do with the poor water condition.If the water conditions are poor and unstable then your fish is likely to get different types of infections which could make them weak and unhealthy.

  • Ich or white spot disease-Antiparasitic treatments are available to treat this ectoparasitic infection. 
  • Fin rot – Fin starts decaying, use antibiotics to treat this condition.
  • Dropsy-Their irregular swimming patterns and swollen bottoms can be treated by giving them salt water baths.
  • Ammonia poisoning- Regular water monitoring can treat this condition
  • Slime disease-A parasitic disease,results in breathing issues,due to bad water conditions.It can be treated by using copper based treatments and salt water baths.
  • Gill parasite- It can cause breathing issues, you can treat this by giving them formalin based medication by consulting your vet.
  • Hole in the head- A parasitic disease which is due to poor water conditions due to overcrowded tank.It could be fatal if left unattended.


  • Harlequin rasboras are active, hardy,easy to care for and a very good beginner fish.They are easily available in fish stores.
  • Always seen shoaling peacefully with other rasboras.
  • Undemanding and dont need an extra ordinary tank setup to keep them.
  • Feed them a healthy and nutritional diet and do water changes to avoid ammonia pollution in the tank.

Frequently asked questions on Harlequin rasboras care

Are harlequin rasboras aggressive fish?

No, harlequins are not aggressive,but are fin nippers.Males show occasional aggression which is normal behavior only.These guys are very peaceful and rarely create chaos in the tank.

Can harlequin tolerate temperature fluctuations?

Harlequin rasboras are hardy species and have adapted to tolerate temperature fluctuations.This doesn’t mean you can keep them in any temperature conditions.They can develop certain skin infections and become lethargic and weak if their tank temperature is extremely below the optimum range.