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How To Stop Oscar Aggression ? (12 Important Tips)

How to stop oscar aggression? since the chances of having an aggressive Oscar are higher, it is worth knowing how to stop oscar’s aggression. Let’s have a look at some approaches to dealing with Oscar’s aggression.

Aggression is one drawback of Oscars when you want a large peaceful tank. But, Oscars are a “Hard Not to Choose” option for many larger tanks and ponds due to their unique coloration, size, and personality. 

If you are lucky enough, your Oscars will be nice as pie and never bother another fish in the tank. Unfortunately, this isn’t always the case, and you may end up with an aggressive Oscar.

How To Stop Oscar Aggression

Why are the Oscars so aggressive?

The Oscars are generally aggressive by nature. These fish are known to be loners in the wild, and they don’t really interact with other fish unless it is mating season. 

The Oscars are also known to be very territorial. They will defend their territories fiercely from any intruder, be it another fish or even their owner’s hand! 

Another reason for Oscar’s aggression is that they are simply very curious creatures. They will often investigate anything new that goes into their tank, which can sometimes lead to aggression if they feel threatened. 

Are all Oscars aggressive?

No, not all Oscars are aggressive.

In fact, many Oscars are very peaceful and will get along with other fish just fine. However, there is always the chance that your Oscar will be aggressive, so it is best to be prepared. 

Will oscar fish kill each other?

Oscar fish are well-known for their ferocity, but they will not necessarily kill each other.

However, if the aggression is not controlled, it can certainly lead to the death of weaker fish in the tank. Therefore, it is critical to take action as soon as possible to stop the aggressiveness.

Are my Oscars fighting or mating?

Sometimes you may misread the signs and think that your Oscars are fighting when they are actually mating.

Mating season for Oscars can be a very aggressive time, and it is not uncommon for fish to chase each other around and nip at each other. 

If you are not sure whether your Oscars are fighting or mating, it is best to consult a fish expert. They will be able to tell you for sure what is going on and whether you need to take any action. 

Some common signs that your oscar is mating include: 

The fish chasing each other around the tank

When a mating pair is getting ready to mate, the male will often chase the female around the tank.

This is usually not a cause for concern and is completely normal behavior. However, if you see this constantly happening and the fish seem to be stressed, it may be a sign that they are not ready to mate, and you should separate them. 

Nipping and biting at each other

Mating pairs of Oscars will often nip and bite at each other. Unless the fish appear to be in pain or the hostility is overwhelming, this is normally not a cause for concern.

Since Oscars are known to kill their mating partner on occasion by being more violent, you should be very careful if you see this behavior. If you notice “extreme” nipping and biting, it’s time to separate the pair.

Building nests out of plants and rocks

Mating Oscars will often build nests out of plants and rocks to lay their eggs. This is a sure sign that Oscars are ready to mate, and you should not separate them. 

Lip locking

Mating Oscars will often lock lips and swim together in what is known as a “lip lock.” This is a sure sign that Oscars are ready to mate, and you should not separate them. 

Spawning (laying eggs)

Once the Oscars have mated, they will lay their eggs in the nest. This is the final stage of the mating process, and you can now separate the fish if they show any aggression towards each other. 

If you are unsure whether your fish are fighting or mating, the best course of action is to consult a fish expert.

How To Stop Oscar Aggression

How To Stop Oscar Aggression

Fish aggression is not something we can control like a light switch. But, there are certain things we can do to reduce the aggression in our oscar fish. Let’s look at some steps for dealing with Oscar’s aggression.

01. Increase The Tank Size

One of the best ways to reduce aggression in your oscar fish is to increase the tank size simply. A larger tank will give your fish more space to move around and give them more places to hide. 

A larger tank will also make it less likely for your fish to feel threatened by each other. This is because there will be more space for each fish to claim their own territory. 

02. Provide More Hiding Places

Another way to reduce aggression in your oscar fish is to provide more hiding places. This will give your fish a place to go if they feel threatened or stressed out. 

Hiding places can be anything from rocks and caves to plants and driftwood. It is essential to provide a variety of hiding places so that each fish can find a place that suits them. 

03. Avoid Overcrowding

Overcrowding fish is one of the main reasons for aggression in fish. This is because fish feel threatened when they are closely packed together. 

It is important to avoid overcrowding your tank. This means not putting too many fish in one tank and not housing different species together. 

04. Reduce Stress

Stress is another key factor that can lead to aggression in fish. There are a number of things that can cause stress in fish, such as poor water quality, lack of hiding places, and even brightly lit tanks. 

It is important to do all you can to reduce stress in your fish. This includes maintaining good water quality, providing plenty of hiding places, and keeping the tank out of direct sunlight. 

05. Introduce New Fish Carefully

When you add new fish to your Oscar tank, it is important to do so carefully. This is because new fish can be a major source of stress for your existing fish. 

Before adding new fish to your tank, you should always quarantine them. This will help to ensure that they are not carrying any diseases or parasites that could harm your other fish. 

You should also introduce new fish gradually. This means adding a few fish at a time over a few days. 

06. Avoid Aggressive Fish

Some fish simply have a higher level of aggression than others. If you are having trouble with aggression in your tank, it might be a good idea to avoid keeping aggressive fish. 

Some of the most aggressive fish include Texas cichlid, green terror, and Jack Dempsey. Only experienced fishkeepers should keep these fish.

However, if you introduce those two species together when they are juveniles, they will usually get along just fine when they grow up.

07. Provide Plenty of Food

Another way to reduce aggression in your oscar is to provide plenty of food. This is because fish are less likely to fight over food when there is plenty to go around. 

It is important to provide diverse foods so that each fish can get the nutrients they need. You should also feed your fish several times a day instead of just once. 

08. Rearrange the decorations

You should also try rearranging the decorations in your tank from time to time. Since Oscars are territorial fish, they may become aggressive if they feel like their territory is being threatened. 

Rearranging the decorations will allow your fish to explore new areas and claim new territories. This can help to reduce aggression in your fish. 

09. Add more target fish

Adding more target fish is another way to reduce aggression in your oscar fish. Target fish are fish that are often big enough and fast enough to escape from oscar bullying.

Since Oscars need something to take out their aggression, they will often leave the other Oscars alone and avert their attention to target fish.

The best option is to choose schooling fish like Bala sharks, tinfoil barbs, and silver dollars for this job.

As schooling fish stay in a school, the harassment of Oscar divides into several fish, so the risk of harm to any particular fish is greatly reduced.

But, be careful. If you see your Oscar is harassing particularly one fish in the school, you will need to take that fish out and put it in another tank as they are living beings too.

10. Separate the aggressive oscar from the tank

If none of the above approaches work and your oscar is still being excessively aggressive, the best method to resolve the problem is to remove the oscar from the tank.

While this may be a drastic solution, it is often the only way to stop the aggression.

If you own more than one oscar fish, you may be able to put the aggressor in a separate tank. However, if you only have one oscar, you will need to find another home for it. 

11. Divide the tank with a tank divider

If you can not afford a separate tank for your aggressive oscar or do not have the space for one, you can try using a tank divider. 

A tank divider is a piece of clear plastic or glass that is placed in the tank to divide it into two separate sections. This can be a temporary or permanent solution depending on your needs. 

Dividing the tank can help to reduce aggression by giving each oscar its own territory. This can be a good solution if you have a small tank and can not afford to get a larger one. 

12. Sell or give away your aggressive oscar

If none of the above approaches work, you may need to sell or give away your oscar. While this may be a difficult decision, it is often the best thing to do for the welfare of your fish. 

When selling or giving away your oscar, be sure to let the new owner know about the fish’s aggression. This way, they can be prepared to deal with the problem. 

With a little patience and effort, you should be able to reduce the aggression in your oscar fish. By following the above tips, you can provide your fish with a safe and peaceful environment.

Related questions

What does it mean when Oscars lock lips?

When two Oscars “lock lips,” it usually means they are about to breed. However, it can also be a sign of aggression. If you see your Oscars locking lips, watch them closely to see if they are fighting or breeding.

Why is my Oscar attacking the glass?

Oscars may attack the glass for a variety of reasons. Sometimes, they mistake their own reflection for another fish.

Other times, they may be trying to establish their territory. If your oscar is attacking the glass, try rearranging the decorations in the tank to see if that helps. If not, you may need to remove the oscar from the tank.

Why does my oscar pick up rocks and spit them out?

Oscars often pick up rocks and spit them out because they are looking for food, redesigning their territory, or building nests for spawning.

However, sometimes this behavior can be a sign of aggression. If your oscar is constantly picking up rocks and spitting them out, try giving them more food.

If that doesn’t help, you might need to try out other oscar aggression stopping options mentioned above.


Oscar aggression is a common problem that many fishkeepers face. However, with a little patience and effort, it is possible to reduce the aggression in your oscar fish.

In fact, some Oscars are even known to become docile and peaceful over time. By following the above tips, you can provide your fish with a safe and peaceful environment.

Credit to : Poseidon’s Pets
Read Next: Signs My Oscar Fish Is Dying? ( 11 Possible Signs )

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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.