Why Are My Cardinal Tetras Chasing Each Other?

Cardinal tetras are peaceful freshwater fish. They get along with most of the tankmates. Moreover, being schooling fishes, they immensely enjoy the company of other cardinal tetras. But some owners often complain that they see Cardinal tetras chasing each other.

So, why do Cardinal tetras chase each other? Since Cardinal tetras are playful and energetic, they might be chasing each other casually when they swim around. Besides this, other reasons for chasing may be establishing territory, competition for food, mating, or dominance.

We will be learning more about the chasing habit of Cardinal tetras in detail in this article. So keep reading to settle all your doubts.

Why Are My Cardinal Tetras Chasing Each Other?

It is not unusual for Cardinal tetras to chase each other, and most of the time, they do not mean it to harm other fish. These fish are highly energetic and friendly and love to bond with other fish, so they sometimes chase each other. Besides this, some of the reasons why Cardinal tetras chase each other are:

When Cardinal Tetras Are Mating

Cardinal tetras are highly energetic fish, and they will do anything to reproduce, including chasing each other. When a male Cardinal tetra spots a female, he becomes very aggressive in his territory and starts chasing the females around while getting closer for mating. If you have a large tank with more than one male, this behavior might be familiar because many male fish compete to get more intimate with females.

While Fighting for Food or Shelter

Cardinal tetras are extremely friendly, and they love socializing with each other. However, this can often lead them into fights because of limited space in your tank. When there is a lack of shelter, food, or territory, these fish become highly aggressive and start chasing each other around. Sometimes, one might feel intimidated and retreat, leaving the rest to fight it out until there is a winner.

If They Feel Scared

Cardinal tetras are not only highly active, but they can also feel terrified, especially when someone or something enters their tank suddenly. When you notice that your Cardinal tetras are chasing each other, you should check if they feel anxious about something or someone. Check every corner of the tank and move anything that makes them feel uncomfortable.

Due To Overcrowding

Cardinal tetras are friendly fish that love to interact with each other. If they don’t have enough space in your tank, these little guys will try anything to get more room, including chasing each other around. However, this is not a very common cause of why Cardinal Tetras pursue one another, so if you see it happening frequently, check if you have more fish than your tank can handle.

While They Are Sick

Cardinal tetras are very active, but they are also susceptible to diseases, so if one of them becomes sick, the rest might start chasing each other to get rid of the disease.

If this is happening with your Cardinal tetras, you should quarantine the sick fish and treat them in a separate tank. It helps to prevent other healthy fish from infection.

When Cardinal Tetras Are Playing

Cardinal tetras are intelligent creatures, to chase each other just for fun. If you notice this behavior in your tank, it means that everyone is healthy and happy but wants to play with their friends. Therefore, it would be best to consider adding more hiding spots or shelters so these fish can express themselves without chasing one another around the whole time.

When They Want To Claim Their Territory

Cardinal tetras love to claim their territory. So sometimes, when a new fish enters the tank, your little friends might start chasing each other around in an attempt to get rid of this intruder. If you notice that all of your Cardinal Tetra fish are running after one another, it means that there is something off with the newcomer.

Due To Change In Water Conditions

The water conditions play a vital role in whether your Cardinal tetras will chase each other or not. For example, if the water is cloudy and contains less oxygen, they may show increased chasing behavior than fish living in clean and well-oxygenated water. In addition, if you have an overstocked tank, this may also lead to chasing.

Is It Ok If Cardinal Tetras Chase Each Other?

Yes, it is normal for Cardinals sometimes to chase each other. However, you need to look out to determine if this behavior among your fish is playful or more aggressive.

Some of the risks that you might experience if your Cardinal tetras are constantly chasing each other are:

  • Fin & Scale Damage
  • Injury to the central nervous system.
  • Even death of one or both cardinal tetras.
  • Stress-related problems includedrops in appetite and changes in behavior or activity levels.

What Should I Do If My Cardinal Tetras Are Chasing Each Other?

If you notice that your Cardinals are chasing each other excessively, it is essential to take action. Some of the tips that will help you manage this behavior of your fish are:

Place Cardinal Tetras In A Right Sized Tank

It would be best if you kept Cardinal tetras in a right-sized tank. If you fail to give the fish enough space to swim, they might start chasing each other. However, suppose you provide your Cardinals with spacious living areas but still notice this behavior between them. In that case, there must be some problem within their social structure that needs urgent attention.

Keep Cardinal Tetras In A Right Number Of Pairs

If you want your Cardinals to live in peace and be happy, it is essential to keep them within the correct number of pairs. It means if there are two Cardinals, one should not be lonely or left alone while the other has a friend with him. Also, if you keep them in pairs, it is less likely that they will start fighting.

Introduce More Hiding Spots

Adding plants and decorations in the tank also helps by providing them with hiding spaces. There should be enough hiding spots available in the aquarium for your Cardinals.

Ideally, there should be a hiding spot at each end of the tank. It will allow them to have their own space and not feel threatened by other fish all the time. You can also add more plants into their environment, which will provide them with an extra layer of security.

Install Tank Dividers

If you have a large tank and notice that your Cardinals are constantly chasing each other, then it is time to think about installing tank dividers. It will separate the fish from one another without causing them any harm or stress. This way, they can happily co-exist in their living space while still having enough room for swimming around.

Provide Enough Food

It is also possible that your Cardinals are chasing each other because they lack food. To prevent this behavior, you need to make sure there is enough fish food available for them at all times. As a result, they do not feel hungry or stressed out due to hunger pangs.


Summing up, Cardinal tetras are very active fish that swim around the aquarium constantly. Their main reason for chasing each other is to establish a social hierarchy. However, they can accidentally hurt their tank mates in the process of setting this order.

Therefore, it is crucial to be attentive as an owner in their care if you want them to live in harmony with their tank mates.

Thanks for giving your time. We appreciate it and hope we could help you with your questions.

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