How Many Angelfish In A 40 Gallon Tank?

You can keep three or four angelfish in a 40-gallon tank. 40 gallons is large enough to allow the angelfish enough room to swim around comfortably.

Angelfish make beautiful additions to a tank. These South American fish are docile when young and become territorial as they mature. To house angelfish successfully, consider keeping a maximum of four mature fish in a forty-gallon tank.

How Many Angelfish To Keep In A 40-Gallon Tank?

A forty-gallon tank is an appropriate size for angelfish. This size tank is perfect for housing between two and four of this species.

Author Dick Mills explains in his 1980s book, “You and Your Aquarium,” that tropical fish need around 12 square inches of space per inch of the fish body.

When angelfish are juvenile, it is possible to house a number in the same forty-gallon tank. Here’s why:

  • Juvenile angelfish are docile and do not tend to fight
  • They are also small and find the forty-gallon sufficient to swim, hide, and thrive.

As they grow, these fish become quite large and begin fighting for dominance in their social hierarchy. Adult angelfish do not typically school, so you may wish to consider removing a few of your fish, especially if they are being bullied by their more dominant tankmates.

Angelfish grow to around six inches in the wild. In captivity, they can reach as large as ten inches. Their large fins and tails make them tall fish, and they enjoy having ample space to swim, lay eggs, and hide.

Consider the following points when deciding how many angelfish to keep in your forty-gallon tank:

  • Try not to separate any pairs from the school of juveniles you initially placed in the tank.
  • If you have not kept juveniles, consider purchasing two or three angelfish for your tank.
  • If you get three, chances are you will witness a pair forming, and you can then remove the third fish.
  • Removing the third fish that is not in a pair minimizes the chances of aggressive behavior toward it.

Angelfish do well with water that is kept clean and has mild currents. Whether you own one or four, maintain the tank by swapping out around thirty percent of the water weekly.

As you change the water, gather as much of the waste material present in the tank as possible. Keeping your tank clean will allow your angelfish to grow steadily and be healthy.

Three Angelfish in Heavily Planted Tank

You must add plants, rocks, gravel or sand, and wood to your angelfish tank.

In the wild, angelfish live in rivers and areas of flooded land. They swim between plants and lay their eggs on plant leaves. They hide between rocks and logs and feel safest with a dark floor beneath them.

In captivity, angelfish will not lay eggs unless they feel safe in an environment that closely resembles their natural habitat of South America.

They become aggressive during spawning season, another reason to keep a maximum of four angelfish in a forty-gallon tank.

When considering the design of your tank, with the added features of plants, rocks, sand or gravel, and wood, it is helpful to visualize the space left for the fish. Add the plants to the outer border and leave the center open for swimming.

With the open swimming space left, imagining more than three or four fully-grown angelfish thriving is difficult.

Will Schools Of Angelfish Fight In A 40-Gallon Tank?

Angelfish are considered by some to be docile and viewed by others to be aggressive. The truth is that, given sufficient, safe living conditions, angelfish are easy-going fish. When they feel threatened, they become aggressive.

A few factors could cause angelfish to become aggressive in a forty-gallon tank:

1. Overcrowding

When too many angelfish are housed in a tank, they can become aggressive. Angelfish are territorial by nature. They form societal hierarchies and fight for dominance.

Male angelfish are particularly aggressive when defending their territory and fighting for dominance in the hierarchy. If too many fish are housed in the tank, you could see fighting among them.

When angelfish are housed with other fish species, it can cause fighting in the tank. Angelfish are predatory by nature and will prey on fish that can fit in their mouths. They will chase and nip at any other fish that make them feel threatened or that enjoy a different temperament to their own.

2. Maturity

Juvenile angelfish are generally docile and peaceful fish. Only when they mature do they begin to vie for dominance among their peers. This phenomenon affects males more than females.

When angelfish mature, they typically form pairs. If one fish is left without a couple, the paired fish may chase the other to defend their territory.

3. Spawning

Angelfish in captivity can only lay eggs on leaves when they feel secure and safe. During spawning, they can be seen defending their eggs and chasing other angelfish and fish of different species away.

4. Unhealthy Living Conditions

Angelfish are sensitive to their living conditions. You must maintain a clean and healthy tank for their benefit.

If the tank is dirty and has waste, they could become stressed. Similarly, if there is a strong current or too much activity from other fish, angelfish often become disgruntled and can become aggressive.

Part of a healthy environment for angelfish must include plants, sand or gravel, rocks, and wood pieces. These allow the fish to live in a natural and safe way for their species.

5. Not Enough Resources

The issue of insufficient resources comes into play primarily when the tank is overcrowded. When too many angelfish are housed together, they feel the need to fight for food, space, hiding places, and swimming space.

To avoid issues of resource shortages, consider housing a maximum of four angelfish in your forty-gallon tank.

How To Know If A 40-Gallon Tank Is Overcrowded

If you have a forty-gallon tank and are currently housing angelfish, you may wonder if your tank is overcrowded.

There are some tell-tale signs that the tank is too crowded:

1. Stunted Growth

Angelfish grow to around six inches in the wild. In captivity, they can reach as large as ten inches. If you notice that your angelfish are not growing as expected, it could mean that there is insufficient space and resources for your fish to thrive.

Angelfish can grow to a large size even in a smaller tank if they have enough room to swim, hide, and rest. When the tank is overcrowded, they defend their territory and fight to survive rather than being free to grow and develop at will.

If your fish are stunted, assess the tank to ensure it is not overcrowded. Both other angelfish and other species of fish can cause overcrowding.

2. Aggression

Although it is common for male angelfish to demonstrate aggression in a tank, it is not typical for there to be constantly fighting.

If your tank is constantly filled with fish nipping, chasing, or lip-locking each other, consider removing one or more fish.

3. Excessive Waste

Fish produce a steady stream of waste, and waste management will be excessive when there are too many in a tank.

If you need to clean out your forty-gallon tank more than once a week, it could mean that your tank is overcrowded.

4. Diseases Among Fish

When tanks are overcrowded, diseases can spread with ease. Angelfish are prone to be affected by Ich, white spot disease, and vibriosis.

When fish are sick, they should be treated with antibiotics if necessary and quarantined. Raise the temperature of their water and add salt to help fish heal from white spot disease.

If your fish are experiencing frequent bouts of illness, assess the environment and consider removing some inhabitants to provide more space and cleaner living conditions for those that remain.


The perfect number of angelfish for a forty-gallon tank is between two and four. When too many angelfish are housed together, they become aggressive, could experience stunted growth, and produce too much waste to ensure a safe environment.