Why Do Aquarium Fish Chase Each Other?

6 min read

IMG 8934 PetAquariums Why Do Aquarium Fish Chase Each Other?

Maintaining an aquarium can be fun and exciting but problems can also arise.

This is how I got involved in aquariums because my wife had an aquarium and when problems arose, I decided to start researching and helping her solve them. One of the main problems that we had to solve was: “Why do aquarium fish chase each other”.

The short answer is

Aquarium fish chase each other because they are:

  • Territorial
  • Incompatible
  • Competing for food
  • Coupling
  • Dominance
  • Sick
  • Playing

When you’re putting together an aquarium, you’re basically trying to mimic your fish’s natural environment in their wild habitat either in saltwater oceans or bodies of freshwater-like lakes.

So, in reality, your fish had a lot more room to move around in their natural habitat than they ever will in your aquarium. A lot of aquarium fish are still captured in the wild, so you can imagine their culture shock at being put in a tiny aquarium compared to roaming an entire ocean, much less a freshwater lake.

With this being said, I recommend saving yourself a headache and just filling your tank with the more amiable species so that you can focus more on enjoying your aquarium.

Once you do get some fish in your aquarium, even if they are bred in captivity, they will display different behaviors based on their personalities. So, let’s get to the first reason for “Why do aquarium fish chase each other“.



We can, in a way, look at fish like our own personalities when it comes to territory. Some fish, like us humans, simply prefer our own space or territory.  Especially if the fish has been in the tank for a while and you introduce a new fish that keeps swimming into the fish’s territory.

If you do have one or more fish that wants their own territory, don’t panic, there are a few things you can try to alleviate the situation:

  1. Make sure your fish are getting plenty of food so that you know this isn’t the issue. Sometimes your fish may just be moody and fighting over food. Usually, if it is territorial you can tell because the aggressive fish will remain in the same area and constantly chase other fish out if they come to close.
  2. If this problem is from introducing a new fish into your aquarium or you have the problem from the very beginning, you can rearrange your aquarium. Just move all of your aquarium ornaments or decorations around so that the fish won’t have the same territories. After you rearrange everything, make sure that there are plenty of other hiding places for all of the fish. If you already spent your budget putting your aquarium together, you can make homemade hiding places. For example, you can make caves out of some of the gravel in your tank or from some leftover gravel that you didn’t use.
  3. The last solution would be to move the aggressive fish into its own tank if possible. After it is in its own tank, you can try to sell it to another fish keeper or even give it away. If you really want to keep it and you are capable, you can always start another aquarium. If the aggression is from breeding fish, you can always temporarily move the love-struck fish into another tank until their romance is complete.


This is common sense but only if you have done your homework prior to getting your fish.

When you first set up your aquarium, the most important decision is what type of fish you are going to have and how many.

You really need to make sure your fish are compatible.

You might be surprised at what you discover. For example, two male betta fish can not be put in the same tank or they will try to kill each other.

betta aquarium fish chase each other

A couple of fish that a lot of people like to keep in aquariums are a guppy and a goldfish, but they are not compatible.

There are way too many good and bad combinations of fish so please do your homework.

A good guideline to follow is to pick fish that live together in the same region of the world, however, you still need to make sure they are compatible.

Competing For Food

A limited food supply will cause any living species to turn against each other.

Here are some tips to keep your fish eating happily:

  • You really need to do your homework.
  • You need to know what type of food each fish eats and make sure they are getting enough.
  • You need to know whether your fish are carnivores, herbivores, or omnivores (plants and meat).
  • Don’t feed your fish more than they can eat in 2–3 minutes. If it starts taking them longer than 2-3 minutes to finish the food you gave them, they are probably full and you don’t want a lot of leftover food in your tank.
  • In the natural world, fish usually eat at dawn and dusk, so it is better to feed them in the morning and at night.
Child fish feeding


Coupling, in laymen’s terms, is what we call dating in the aquarium world. This can cause fish to chase each other for a number of reasons:

  • Two males are competing for the same female.
  • The female is chasing the male to let him know she is ready to date or to make him leave her alone.
  • The male is chasing the female to let her know he is ready to date.

The best ways to alleviate this situation are to leave it alone if no fish are being harmed or to make sure there are 2–3 females for every male fish in the tank.


This is usually just a case of one of the male fish showing dominance over all the other male fish. It might seem unusual in fish but at the end of the day, they are animals like your other pets.

There is usually a male or two that wants to be the alpha male and will chase the other fish around the tank. This is how the fish react in their natural wild environment, so it is to be expected sometimes in your tank.

To solve this, you can try to keep more fish in your tank. This type of bullying is more likely to happen if there is a smaller group of fish in your tank. Or the ultimate solution for any fish-chasing situation is to simply remove the problem fish and put them in their own tank.

Is Your Fish Sick?

Sick fish can be aggressive and other fish sometimes are aggressive towards a sick fish. Try to keep an eye on your fish to see if they have any of these warning signs:

  • Swimming disoriented, at weird angles, or even upside down.
  • They don’t eat all their food.
  • Unusual spotting on their body, especially white spots.
  • Gills are an unusual color.
  • Sometimes it will look like your fish is trying to catch its breath on the water’s surface.
  • Their eyes are bulging.
  • They have a film of mucous on their body.
  • Are they rubbing against hard surfaces?
  • They are alone from your other fish when they usually hang out together.
  • Any type of markings like a sore or a lesion.
  • I know this sounds weird, but do they look bloated?

Remember, if your fish seems sick or even if you aren’t sure, you can always take your pet fish to the vet.


Last but not least, your fish may just be playing with each other. If it looks like one of your fish is chasing another but they are not really showing aggression, then they may just be playing with each other. Experts have found evidence to show that fish do play with each other.


Okay, ladies and gentlemen. I hope I have shared enough info to answer your question: Why do aquarium fish chase each other?

It is important to do your research first to find out which fish are compatible and have the same diet as this will eliminate a lot of problems when it comes to your fish chasing each other.

Hopefully, you can figure out why they are doing it and come up with a solution so you don’t have to move one of your fish to a new tank or give it away.

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Pet Aquariums

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