How many Harlequin rasboras in a 40-gallon tank?

In this post, we will discuss the topic “How many Harlequin rasboras in a 40-gallon tank” and all steps of setting up a Harlequin rasbora aquarium.

How many Harlequin rasboras in a 40-gallon tank

A 40-gallon tank can fit 10 to 12 Harlequin rasboras. As Harlequin rasboras are very active swimmers, the general rule for this species is 2 gallons of water per inch of fish. 

Harlequin rasboras can grow up to 2 inches. However, most of them grow only 1.5 or 1.75 inches. For this reason, the limiting number of Harlequin rasboras in a 40-gallon tank is 12. Additionally to the fish, in a freshwater tank, plants, substrate, and equipment also require space. Keep that in mind to not overcrowd your tank when calculating the fish quantity.

If you are considering a 40-gallon community tank, it is also important to consider the tank mates personalities and requirements. Thus, the total number of Harlequin rasbora would probably reduce. 

What you should know about Harlequin rasboras 

The most common rasbora variety found in freshwater home tanks is the Harlequin rasbora. Their pink to orange colours and personalities give awesome look to an aquarium, as well as great dynamics. Harlequin rasboras are small fish that measure up to 2 inches. Although, most of them measure around 1.5 to 1.75 inches when adult. Their lifespan is around 5 years but can be prolonged until 8 years if the ideal tank and water conditions are followed and the fish are well cared for.

Harlequin rasboras require very low effort and attention from the owner. However, it is important to keep water parameters and tank conditions stable. Harlequin rasboras are beginner-friendly, which means they do not require expertise in aquariums. 

These fish are shoaling fish. They do better if they are in groups of at least 5 Harlequin rasboras. When in groups, Harlequin rasboras Their swimming performances are extraordinarily awesome to watch.

Sexual dimorphism is quite clear in Harlequin rasboras. Males have larger black patches and are smaller than females. Additionally, in males, the triangular patch has a rounded bottom, while in females, the patch bottom is sharp.

What do Harlequin rasboras eat?

Harlequin rasboras are omnivorous fish. They naturally feed on invertebrates, small shrimp, and some larvae. They can also be fed using industrialized fish flakes and pellets. They appreciate live and frozen-dried food.

Who are the best Harlequin rasboras tankmates?

Harlequin rasboras are extremely pacific. They are just perfect for community tanks as they do well with several fish and non-fish species. They will never perform fin-nipping or other aggressive behaviours.

The only limitation about tank mates is the size difference. They are very small fish, and thus, they do not do well with aggressive larger fish species, as they would probably become prey.

It is also very important to provide plenty of conspecifics before thinking about mates of other species. They are highly social fish, thus keeping a group of at least 5 Harlequin rasboras is a must.

Some of the best Harlequin rasboras tank mates are small peaceful fish species that have similar requirements to the Harlequin rasbora and do well with active swimmers.

–       Harlequin rasboras: These are the first tankmates a Harlequin rasbora should get. They are very social fish, and thus, need to be kept in groups;

–       Neon and Cardinal Tetras: They are small and do not grow to more than 1.5 inches, these are also very social fish. Hus, they also need to be in groups of at least 6 individuals;

–       Corydoras: They can grow up to 2.5 inches and are peaceful bottom-dwellers. Thus, they will not bother the Harlequin rasboras. They appreciate being in small groups of a minimum of 4 individuals;

–       Small Plecos: These are extremely peaceful fish, that usually grow further than the Harlequin rasboras. They are bottom-dwellers, thus they will rarely meet the Harlequin rasboras. 

–       Danios: Danios are also schooling fish that appreciate groups of at least 6 individuals. They are peaceful and non-aggressive that grow up to 2.5 inches;

–       Dwarf Gourami: These are also non-aggressive and pacific fish. They can grow around 3.5 inches and will not bother the Harlequin rasboras;

–       Guppies: These are also schooling fish that require a group with a minimum of 8 individuals. They are also very peaceful active swimmers that can grow around 1.5 inches.;

–       Snails: They will help you with tank cleaning and avoid leftovers and are not able to bother the Harlequin rasboras;

–       Shrimp: These animals will also help with tank cleaning. They will also not bother the Harlequin rasboras. However, try not to get too small or too big to avoid any potential issues.

Tank conditions to keep Harlequin rasboras

As stated above, Harlequin rasboras are low maintenance fish. However, it is still necessary to keep good water quality and adequate tank conditions. 

Water parameters

Harlequin rasboras water temperature range is between 72 and 82 degrees Fahrenheit and pH levels should vary between 6 and 7.8.

Plants & Substrate

Harlequin rasboras are original to well-planted areas. Thus, keeping some plant species is required and well appreciated. The plants provide hiding spots and protection for the fish. Harlequin rasboras appreciate plants with broad leaves.

A good substrate can be very important for the fish as well. Thus, getting gravel or sand would be good for the Harlequin. A mix of these two types would work very well. Gravel is also easier for the plants to attach and thrive. Additionally, opting for a darker substrate contrasting with the Harlequin rasboras colours will give a better look to the aquarium.

40-gallon community tank combinations with Harlequin rasboras

Considering the fish temperament and specific tank requirements, it is possible to draw some potential combinations for community fish tanks with Harlequin rasboras. Also, we considered some freshwater invertebrates, such as snails and shrimp.

Here are some possible fish combinations for a 40-gallon tank with Harlequin rasboras are:

1.   6 Harlequin rasboras + 4 Corydoras catfish + 6 Neon tetras;

2.   6 Harlequin rasboras + 2 Bristlenose plecos + 5 Mystery snails;

3.   8 Harlequin rasboras + 8 Guppies + 5 Amano or Cherry shrimp;

4.   5 Harlequin rasboras + 2 Dwarf Gouramis + 4 Corydoras catfish;

5.   10 Harlequin rasboras + 5 Mystery snails + 5 Amano or Cherry shrimp.


In this post, we discussed “How many Harlequin rasboras in a 40-gallon tank” and all steps of setting up a Harlequin rasbora aquarium.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): How many Harlequin rasboras in a 40-gallon tank

What can you put with Harlequin rasboras?

Several species make great tankmates to Harlequin rasboras. The ideal Harlequin rasboras companies are other small peaceful fish, such as Corydoras catfish, Guppies, Neon or Cardinal Tetras, Mollies, Dwarf Gouramis, and others. It is also possible to house some invertebrates with Harlequin rasboras, such as Mystery snails and Amano and Cherry shrimp.

What plants do Harlequin rasboras like in a tank?

Due to the Harlequin rasbora natural habitat, keeping plants in the tank is quite important for this species. Well-planted tanks resemble their habitat. Thus, they tend to feel safer with plenty of plants. Some good options are dense plants, such as Cryptocoryne. Harlequin rasboras appreciate species with broad leaves.

What do Harlequin rasboras eat?

Harlequin rasboras are omnivores. Thus, they can be fed with industrialized flakes or pellets and live foods as supplements, such as daphnia, larvae, and brine shrimp. It is also possible to offer them freeze-dried bloodworms or tubifex worms and some vegetables.

Do rasboras like water flow?

Harlequin rasboras prefer slow-moving waters. They naturally occupy slow-moving water bodies. However, they can handle well a medium water flow in a tank. 

Can Harlequin rasboras live with Angelfish?

Yes, Harlequin rasboras can live with Angelfish. However, it is important to observe them at the beginning, as the Angelfish could start chasing the rasboras. If that happens, it is recommended to split them into another tank.

Can Guppies live with Harlequin rasboras?

Yes, Guppies can live very peacefully with Harlequin Rasboras. They both can live in fish communities and not perform any aggressive behaviours or fin-nipping.


Stanton, L. 2021. How Many Rasboras Can You Have In a 5, 10 & 20 Gallon Tank?

Yang, A. 2020. Harlequin Rasbora Care: Size, Tank Mates, Breeding & More.

Stanton, L. 2021. 15 Best Tank Mates for Harlequin Rasboras (With Pictures).

Edmond, A. Harlequin Rasbora: Everything You Need To Know.