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why do fish chase each other

Why Do Fish Chase Each Other?

Fish are fascinating creatures, endlessly entertaining themselves as they swim around their tanks.  Tanks that we spend an inordinate amount of time and money perfectly curating for them.

As experienced fish owners will know, they all have their own personalities that shine through in their behavior.  Some are playful while others are mischievous, some are happy to just keep swimming. 

Sometimes, however, their behaviour can be perplexing.  For example, when your fish chase each other around their tank for hours…and hours.

This behaviour might seem unsettling, especially if your fish haven’t exhibited it before, but rest assured that it is usually normal, healthy behaviour for fish. There are many reasons why fish might chase each other, below we will explore some of the most common ones. 

Why Do Fish Chase Each Other?

Courtship And Mating.

During the mating season for your species of fish, it is normal for your fish to chase each other more than usual.  There are three types of chasing that can happen during this time.

Males may chase other males in a bid to determine who is the most dominant, both for their own benefit and to show the females who would be the best mating partner.

Male fish will also chase female fish in a bid to court them into mating.  Finally, female fish may also chase male fish from time to time.  In the case of females chasing males, they may do so either to show a male that they are ready to mate or to chase off an overzealous male. 


While there is not a lot of research into whether fish play, there is some evidence that suggests they do play with objects.  You might have seen your fish throwing their gravel around their tank for instance.

If your fish are chasing each other and there is no evidence to suggest that there is any aggression or any other reason, it is perfectly possible that they are simply playing with each other.

Schooling and Shoaling species are known to be social fish and are likely to play with one another.

fish chasing each other
Schooling fish like to stick together.

Showing Dominance.

As with many groups in the animal kingdom, fish form hierarchies of dominance.

You may notice one or two of your fish often chase other fish in your tank, these are most likely male fish establishing dominance within the group or reminding the group who’s boss.  This behavior is particularly common among guppy fish.  

This type of chasing is not usually a cause for concern, however, if your tank only contains male fish or a small number of fish, the dominant males can end up bullying or fighting with the other fish. 

To avoid this, try to keep bigger groups of mixed fish so that the dominant fish can spread their energies between more fish.


This one is more likely to occur in a tank containing mixed species.  There are some species of fish that are simply less likely to get along, and the confined environment of a tank can exacerbate this. 

There are also certain species of fish that are prone to higher levels of aggression, such as cichlid fish.  

There is also the issue of temperament to consider when placing multiple species of fish in the same tank.  Placing dominant species with placid, lower energy species can result in harassment between fish. 

Territorial fish also do not mix well with other species.  If you are keen to have a mixed aquarium, it is important to do proper research on compatible species before committing to certain fish.  

Competition For Food.

fish being chased
Time for dinner!

This is a common problem for inexperienced, mixed aquarium owners.  Different fish species require specific diets and different nutrients. 

When fish are not getting enough food or enough of the nutrients they need, they can become aggressive or chase each other in a bid to get enough of the limited resources for survival. 

This can result in dominant fish overpowering weaker fish, meaning that the weaker fish are left with little food to eat.  

To avoid your fish chasing each other to compete for food, ensure that you are providing the correct type of food for your particular species. 

Research into the specific dietary requirements of your species can help make sure you are providing the correct type of food for your fish.  Feeding at regular intervals is a useful way to avoid competition for food too.

Space And Territory.

Sometimes fish will chase each other in an attempt to create more space for themselves or to protect a territory they are establishing. 

This type of chasing is often non-aggressive, but is not ideal either and can cause a lot of stress for fish on both sides of the chasing.  There are many reasons why a fish may want to create more space or protect a territory within an aquarium.  

The most common reason however is to do with tank size and setup.  If a tank is too small for the amount of fish, space can become a scarce resource.  Fish will try to protect their space to allow them to move more freely. 

Similarly, if the tank is physically big enough to contain your fish but is overcrowded with plants, toys, or ornaments, chasing may become more common among your fish.  Sometimes less is more.  

Fortunately, these are both easily remedied problems and your fish can be back to their happy selves in no time.

Final Thoughts.

On the whole, chasing each other is a normal, healthy fish behaviour.  It is a way for your fish to interact, play, and communicate with each other. 

If there is no aggression or extreme chasing between your fish, there is no issue or cause for concern.  

However, if the chasing becomes aggressive or excessive, it may be necessary to separate your fish temporarily until you find the cause and can provide a remedy to restore balance within your aquarium.

Remember to always do your research before purchasing fish to ensure you have the correct environment, companions, and food for them.

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