Fish Compatibility: Which fishes should not be put together?

We humans prefer to live in a locality that we like and among the people we like. The same is true with fishes too. The closer the fish tank ambience will be to their natural habitat, the more comfortable they will feel.

Some fishes like to live in a bare bottom tank, some in a planted tank. Some prefer dim light, some prefer not so dim light. Same is true for water temperature, pH levels, as well as the other kinds of fishes that live with them.

Unlike other pets, mutual compatibility is a big deal with fishes. That’s because dogs don’t eat dogs, cats don’t eat cats, but some fishes do eat some other fishes.

In this article, we will cover some of the aggressive fish breeds that should not be kept with other gentler fishes, as well as some incompatible fish breed types.

Table of Contents
  • Tank breed fish or Wild fish
  • Compatibility based on Aquarium Conditions
  • Fish Incompatibility based on Size
  • Fish Compatibility based on Food Eating Zones
  • What types of fishes can live together in an aquarium?

Tank breed fish or Wild fish

The behaviour of a fish is determined by some of the following factors:

  • Tank breed fishes Vs. Wild fishes
  • Natural fishes Vs. Man-made fishes

Fishes that have lived in an aquarium all their life will be different than those that have been caught from the wild, i.e. from ponds, rivers, and oceans. It is true for any animal – e.g. you can always tell whether a lion was born in the zoo or was caught from the wild and brought in.

Natural fishes (especially caught from the wild) are generally more aggressive than tank breed, man-made fishes.

For example, Gold fishes are slow-moving, man-made, tank-breed fishes, and so are less aggressive. If you will keep Barbs, Angel fishes with them, then they may hurt Gold fishes a bit, e.g. by biting their fins, etc.

Natural fishes Vs. Man-made fishes

Though most of the fish breeds are natural (almost 90-95%), some are man-made. Examples of some man-made fishes are Goldfish, Flowerhorn fish, etc. Man-made fishes are obviously tank breed. So, behaviour of natural fishes and man-made fishes vary a bit.


Wild fishes will take some time to adjust to tank life. You will have to make sure that the conditions are perfect for their survival. Fishes that were born in a tank are already used to those living conditions. So, they are easier to manage.

Compatibility based on Aquarium Conditions

It’s obvious that only those fishes can live together that can tolerate similar living conditions.

If you are getting a natural fish, then you must know where they are found in the world – India, South America, Africa, etc. It will tell you whether that fish is a warm-water, or cold-water fish, what pH level they find comfortable, whether they live in clean water or dark muddy water, what other kinds of fishes live with them in the natural world, what type of diet they take, etc.

For example, if you will keep warm-water fishes along with cold-water fishes, then one of them will definitely suffer.

Fishes from the same geological location will probably have a similar diet. This is also a factor in fish compatibility. Such fishes will be more compatible with each other.


Some South-American fishes are: Corydoras (they are Catfishes), Sting Rays, Geophagus cichlids, Arowana, etc.


Some fish species are more adaptable than others. While some are very sensitive to their environment.

Fish Incompatibility based on Size

A basic rule with fishes is that, a fish will eat anything that fits in its mouth. So, if you are keeping small fishes along with large fishes in a tank, then probably you won’t find the small fishes in your aquarium in a few days. As far as possible, keep similar size fishes together.

For example, Gold fishes may eat the kids of Guppy fishes (sometimes even grown Guppies too). That’s because they can fit in their mouth. A fish will eat what fits in its mouth.

Fish Compatibility based on Food Eating Zones

Apart from fishes attacking other fishes and killing/eating them, there is one other factor that we need to keep in mind while we talk about mutual compatibility of various breeds of fishes – their food eating zones.

There are three types of fishes, when it comes to the area inside the aquarium from which they get their food:

  • Top-level feeders – They tend to eat the food that is floating on the surface of the water, or that is near the top. For example, Guppies, Mollies, Swordfish, Arowana, etc.
  • Mid-level feeders – They tend to eat the food that is floating in the middle of the water. For example, Tetras, Barbs, Angel fishes, Rainbows, Cichlids, etc.
  • Bottom-level feeders – They tend to eat their food from the bottom of the fish tank. For example, Catfishes (e.g. Corydoras), Loaches, etc.

Though this is not a water-tight compartmentalization. For example, though Angel fishes are majorly mid-level feeders, but they can come up and eat food floating at the top too.

In our aquarium there should be an optimum mix of these different types of fishes. So, that no food gets wasted. Also make sure that they all can live peacefully with each other.

For example, if you want to keep Angel fishes, then it means that mid-level of your aquarium is covered. So, you should not keep Tetras with them for two reasons:

  • Both Angel fishes and Tetras are mid-level feeders. So, they will fight for food at the middle of the fish tank, and the food floating at the top of the water and at the bottom will get wasted.
  • Even bigger issue is that Angel fishes can eat Tetras!

In a 3 feet tank, we can keep:

  • 4-6 Angel fishes – they will eat the food floating in the middle of the tank. They can also eat the food at the top.
  • With them we can keep 4 Catfishes (e.g. Corydoras) that will eat the food at the bottom.

Some fishes are scavengers, i.e. they only eat dead fishes. Such fishes are generally compatible with all other fish breeds.

What types of fishes can live together in an aquarium?

Now, let’s see the compatible fishes that we can keep with some of the most popular fishes. Fishes that can live together are often referred to as “Tank mates”.

We will also have a look at the fishes that are incompatible, i.e. fishes that cannot be kept together in the same fish tank. (Fish Incompatibility based on Breed Type)

If you will keep incompatible fishes together, then the weaker fish breed will:

  • get killed
  • get beaten up, hurt
  • get cornered - they will always look scared and will try to hide from dominant fishes
  • get sick

Compatibility has to be seen not only on the basis of fish breed, but also sub-breed types, male-female, etc. Even fishes that are of exactly the same breed may differ a bit – stronger fishes may dominate weaker fishes.

What fishes can be kept with Gold fishes?

Ideally, we should not keep any other fish with gold fishes. Gold fishes are slow-moving, tank-breed, man-made fishes, and so are less aggressive. Most other natural fishes can hurt them, even if they do not kill them. If you will keep Barbs, Angel fishes with them, then they may hurt Gold fishes a bit, e.g. by biting their fins, etc.

Also, we often prefer to keep Gold fishes in bare bottom tanks, because they eat a lot and create a lost of waste. Bare bottom tanks are easier to clean. However, in case of most natural fishes, we prefer a planted fish tank.

Gold fishes may eat the kids of Guppy fishes (sometimes even grown Guppies too). That’s because they can fit in their mouth. A fish will eat what fits in its mouth.

Even sub-breeds of Gold fishes may not be compatible. For example, you should not keep Oranda Gold fish with Comet Gold fish. Comet Gold fishes are fast-moving, and they will dominate Oranda Gold fish, and even beat them up.

However, Koi fishes are considered compatible with Goldfishes.

What fishes can be kept with Guppy fishes?

If you already have Guppies (they are top-level feeders), and want to add a few other fish breeds to build a fish community, then here are some of the fish breeds that you may consider:

  • Rainbows – they will eat at the mid-level
  • Catfishes (e.g. Corydoras) – they will eat at the bottom

Other fishes that you can keep with Guppies are – Platies, Female betta, Loaches, Swordtail, Tetras, etc.

Do not keep these fishes with Guppies – Gold fishes, Cichlids, Mollies, etc. Though Gold fishes and Mollies are compatible with Guppies, they do eat Guppies’ kids.

What fishes can be kept with Angel fishes?

Male Angel fishes protect their females, but they often fight with other male Angel fishes. So, the weaker Angel fish males will often get hurt, their fins broken, they will often get cornered, and fall sick.

As we already saw, we can keep Catfishes (e.g. Corydoras) with Angel fishes. We can also keep these fishes with Angel fishes – Barbs, Gouramis, Mollies, Loaches, Platies, Rainbow fish, Sharks, Swordtail, etc.

Angel fishes can eat Tetras (cardinal tetras, neon tetras, etc.). So, they are not compatible. Some other incompatible fishes with Angel fishes are – Discus, Female Betta, Gold fish, Guppies, Koi, Oscars, etc.

What fishes can be kept with Betta fishes?

They are generally found in rice paddy fields. They spend all their life in a very small part of water-logged rice-fields.

Male Betta fishes are called fighter fishes, as they are very aggressive in nature. A male betta may even kill a female betta if they are kept together for long time. That’s why fish breeders separate them after breeding.

So, you should keep betta fishes separately. That is, keep male and female bettas separately. That’s how they are in natural world. They only meet for breeding, and then they move away.

The following fishes are compatible with female betta – Guppies, Mollies, Platies, Rainbow fish, Swordtail, Tetras, etc.

The following fishes are incompatible with female betta – Angel fishes, Barbs, Discus, Gold fish, Gouramis, Koi, Oscars, Sharks, etc.

Predator fishes

There are some predator type fishes, that are more aggressive and prone to attack other fishes. For example:

  • Arowana
  • Redtail Catfish
  • Alligator Gar
  • Wolfish
  • Snake head
  • Vampire fish
  • Goliath Tiger fish
  • Red bellied Piranha

These should never be kept with gentle fishes like Guppies, Gold fishes, Angel fishes, Mollies, etc. Keep them in a separate tank.

Territorial fishes

Some fishes are very territorial, and will attack other fishes if they venture into their territory. For example:

  • Cichlids – They are extremely territorial and will fight with other fishes for their territory. They get so aggressive that they may even kill some weaker fish breeds. However, if food is in good amount, their aggression reduces. Flowerhorn are also cichlids. So, you can keep them with other cichlids. But compatibility is more if they are kept together from a young age.
  • Oscar fish – These are very territorial fishes, and try to dominate and even eat other fishes. For this they use suction technique.
  • Barbs – They are territorial, and can attack other fishes. But they are not as aggressive as Cichlids.

For more information, you can google “fish compatibility chart”. You will get many charts in the image section. However, make sure to refer to 2-3 charts, as there may be some mistakes in these charts.


Sometimes you will see even incompatible fishes living peacefully together in the same fish tank. It can happen if all these fish breeds are kept together from a very young age. Growing up together in a confined space creates a bond between them.

Also, if they live in clean water, healthy environment, and get enough food, then they don’t get any excuse to fight with each other. However, if the conditions worsen, they may attack each other, because genetic predisposition may be suspended but not eliminated.

There are many such examples in animal kingdom. For example, you may have seen Cats and Dogs, and even Parrots and Rabbits living together in the same house. Sometimes, this also happens in the wild. Inter-species friendship is uncommon, but not rare.

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