Are Oscar Fish Aggressive? {Top 8 Ways To Reduce Oscar Fish Aggression}

Do you want to make sure you can keep an Oscar fish living peacefully in your tank? Will your Oscar fish eat, bully and stress out tankmates? In this article, we’ll find out if Oscar fish are aggressive.

Are Oscar Fish Aggressive? Yes. Oscar fish are considered semi-aggressive members of the cichlid family who are territorial by nature. They may try to eat tankmates that can fit into their mouths, especially if they are continuously swimming in the territories that your Oscar fish has claimed.

Poor water quality and insufficient tank sizes will also encourage aggression. Let’s dive deeper and find out all there is know about why Oscar fish are aggressive and how we can limit it.

Are Oscar Fish Territorial?

Yes. Your Oscar fish could look to claim a territory in your tank and aggressively defend it. There are over two thousand species classified under cichlids including Oscar fish.

They are also called:

  • Velvet Cichlid
  • Tiger Oscar
  • Marble Cichlid

In South America, specifically in slow-moving waters around the Amazon River basin, you can find Oscar fish staking out territories under fallen branches and other vegetation.

Rearrange your decorations from time to time to force your Oscar fish to adapt to changes and loosen up on aggression from defending certain areas in the tank.

What Are the Water Parameters for Oscar Fish?

Oscar fish can make a mess with the amount of waste they produce in your tank. Nevertheless it is important to maintain optimal water parameters to reduce Oscar fish aggression.

Most importantly you must keep a single Oscar in a tank that is 75 gallons or above. Disregard suggested recommendations for one Oscar in a 55 gallon tank if you wish to minimize any chance of aggression.

The following water parameters are suitable for Oscar fish:

  • Temperature: 74°-81°F
  • Ammonia/Nitrite: 0.
  • Nitrate: <20 ppm.
  • pH: 6.0-8.0
  • Water Hardness: 5-20 KH

Will An Oscar Eat Other Fish?

Yes. Oscar fish are notorious for eating fish that are smaller than them. If they can fit any tankmate into their mouths, it will become their next meal.

Oscar fish are known to be predators in the wild. They enjoy eating small fish, insects, larvae and crustaceans with small amounts of plant matter as well.

If you are feeding your Oscar fish live foods or feeder fish, you are increasing the likelihood that your Oscar fish may eat a tankmate smaller than it.

Keep tank mates that are of a similar size or swim in the bottom layer of your tank that will keep it away from your Oscar fish.

YouTube video

How Do You Stop Oscar Fish Aggression?

There are multiple methods that you can adopt to reduce the aggression you are noticing in your Oscar fish.

Here are our top 8 recommendations:

  1. Rearrange the decorations and plants.
  2. Add plenty of hiding spaces. 
  3. Keep only one single Oscar fish in a 75 gallon tank.
  4. Avoid timid or shy top and mid-level swimming tankmates. 
  5. Keep your Oscar fish well fed 1-3 times a day with enough food it can eat in 3 minutes.
  6. Remove leftovers to limit ammonia spikes. 
  7. Keep the tank clean with optimal water parameters for this species.
  8. Maintain temperatures between 74°-81°F with a heater.

You want your Oscar fish to swim in clean water to reduce stress, but you also want them to have spacious room and hiding spaces to cool out and relax.

There should be no hunger or competition for food, but cleaning up leftovers 3 minutes after meals are introduced will go a long way to keep the tank clean when your Oscar fish is notorious for making it messy.

What Fish Do Oscars Get Along With?

Would you like to know which tankmates are suitable for Oscar fish? We like to recommend keeping Oscar fish alone in a single species tank if possible. Make sure you have a tank that is 75 gallons or larger.

Here are some tank mates that have fared well with Oscar fish:

  • Corydora catfish
  • Sailfin Pleco
  • Otocinclus catfish
  • Silver Dollar fish
  • Firemouth cichlids
  • Convict cichlids
  • Blue acara

An Oscar fish will not get lonely on its own. Do not add fish that are small enough to fit into its mouth if you want them to remain alive.

Stick with fish that are larger than 5 inches. Shy fish may end up getting chased around by your Oscar fish.

Bottom dwellers are recommended because they will stay out of the way when your Oscar fish prefers to swim at the top or mid-level of the tank.

Do Oscars Bite Humans?

Oscar fish are not known to bite humans. Your fingers should be safe but it’s always best to wear gloves when you’re messing around inside the tank.

The bite of an Oscar may hurt if there is an accident, but it will only be a minor wound. On the other hand, an Oscar fish bite may inflict enough damage on a tankmate to cause a serious wound, injury or death.

How Do Oscars Fight?

Oscar fish do not need to be kept in groups. They may fight each other by locking lips or jaws. You may notice Oscar fish swimming around in circles looking for a chance to bite each other.

They may do so out of competition for food or to exert dominance in their hierarchy. We’ve even seen a single Oscar fish trying to attack its own reflection in the glass!

This is not to say that all Oscar fish fight. So much depends on the individual personality of each Oscar fish and the conditions in your tank; specifically the tank size and water chemistry.


An Oscar fish can be easily irritated if tank conditions are not right. Even though they are messy fish that produce a lot of waste, they look to you to keep things clean to keep them calm.

Overcrowding and unsuitable tankmates with a lack of hiding spaces invites Oscar fish aggression that can be prevented by following some of the tips we presented today in the article above.


Thank you for visiting for all your informational needs regarding Oscar fish and plenty of other Aquatic Life that we enjoy keeping in our tanks. Please come back again soon and check out another article that may pique your interest. Bye for now!

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.

Recent Posts