Are Oscar Fish Aggressive: Causes & Prevention

Oscar fish, also known as cichlids, are popular pet fish. While they can be hardy, making them a good choice for beginners, they are also often considered to be one of the most difficult fish to keep. If you have one, you might be wondering if they are aggressive?

Yes, Oscar fish are aggressive due to different reasons. If you have an Oscar fish, it is important to be aware of their nature and how to handle them if they become aggressive. In this article, we will discuss the nature of Oscars and why they may be aggressive.

Oscar fish Astronotus ocellatus swimming underwater aquarium

How Do Oscar Fish Show Aggression?

The fish show aggression through high energy levels and a tendency to nip at fingers and toes. Oscar fish use their sharp teeth and strong jaws to fight for what they want. In some cases, they use their scales and fins to fight off predators and competitors.

Why Are Oscar Fish Aggressive?

Insufficient Aquarium Space

Oscar fish are known for their aggressive behavior. This may be because there is not enough space in the tank to accommodate all of them. This can lead to them attacking other fish in the tank, and can also lead to them injuring themselves. It is important to keep Oscar fish in tanks that have enough space so that they can behave themselves, and not attack other fish. It is important to find a tank size where there is enough space for your pet, but limit how many you have at one time because these fish need oxygen to breathe naturally.


Oscar fish are often considered aggressive because they are stressed. In the wild, Oscar fish are constantly fighting for food and space. This constant competition can lead to stress, which in turn can lead to aggression. Some people believe that this is because the Oscars are stressed out due to the high pressure of the competition.


Oscar fish are known for their territorial instincts. Whenever another Oscar enters the ocean, it will pick a fight with them to establish dominance and territory over what is rightfully theirs in their home. Some believe that the aggressiveness of Oscars is because they want to show dominance over their surroundings. Others believe that it is simply a way to survive in a competitive environment. Regardless of the reason, Oscar fish are often considered to be one of the more aggressive fish species.

Inadequate Food

This is the main reason behind Oscar fish’s aggression. Many owners suggest that Oscars become aggressive when they do not receive enough food, or when they are no longer able to consume their favorite foods. In extreme cases of starvation, these types of fishes sometimes eat other smaller fish in tanks and even cannibalize them unless provided with a large amount of nutrients that normally comes from feedings by predators like shrimp or snails – which will also be eaten.

Unfavorable Water Parameters

Oscar fish can also become aggressive because the water parameters are not right. These fish thrive in environments with high levels of dissolved oxygen and a pH level of 6.0 to 7.5. However, many Oscars are kept in tanks that do not meet these standards and they become aggressive as a result.

Can Oscar Fish Kill Each Other?

Oscar fish are a popular aquarium fish, but their aggressive behavior can be dangerous to their tankmates. In a study of Oscar fish in captivity, it was found that the more aggressive Oscars tended to kill their less aggressive tank mates. This behavior is likely due to the fact that the more aggressive Oscar can monopolize food and territory, which can lead to the death of its tankmate.

closeup of a tiger oscar fish, a tropical aquarium pet from the ocean of south America

How to Stop Oscar Fish Aggression?

Get a Bigger Aquarium

Many Oscar fish become aggressive because they do not have enough tank space. These fishes typically get along well with other species but are extremely territorial and violent with their group when there is too much interference between the two groups. We recommend that you research your Oscar before adding it to an existing setup or by getting it a separate tank that will allow for more room for swimming and feeding behavior of this unique fish – better yet, buy one all to yourself to ensure you have enough space for aggressive behavior and tankmate interaction.

Feed Them Regularly

Oscar fish are commonly kept in home aquariums and are known for their lively personalities and playful antics. However, like all fish, Oscar fish can become aggressive when they feel threatened or when they are not getting the food they need. There are a few things that you can do to help prevent Oscar fish aggression from occurring and to ensure that they get the food they need.

Oscar fish are known for their aggressive behavior. This can be a problem because they can damage other fish or plants in their tank. To prevent this, it is important to feed the Oscar fish the right way.

Provide Healthy Environment

Stress is one of the biggest factors that can contribute to aggression in fish. To help your Oscar fish live a stress-free life, it is important to create an environment that is calming and relaxing. Some things you can do to create this environment include providing plenty of hiding spots, providing plenty of aquatic vegetation to explore, and adding a few calm, peaceful fish to the tank.

Stabilize Water Parameters

When it comes to keeping aquarium fish, it is important to maintain water parameters to prevent aggression. Aquariums with high levels of nitrates or phosphates can cause fish to become aggressive. Additionally, a lack of oxygen can also cause aggression. By monitoring water parameters and adjusting them as needed, you can help keep your aquarium fish happy and healthy. Water parameters for Oscars can be maintained to prevent their aggression. For example, a pH level of 6.5 to 7.0 is necessary for the fish’s optimal health and growth. When the pH levels drop below 6.5, it can result in aggressive behavior. Additionally, maintaining a specific temperature range of 74 to 81 degrees Fahrenheit (23 to 27 degrees Celsius) is necessary to prevent stress and aggression in the fish.

Create Hiding Spots

Oscar fish are known for their aggression because they might be lacking resources inside your aquarium where they can explore. They can be territorial and aggressive towards other fish. Some people have suggested that hiding places for Oscar fish to stop their aggression would be beneficial. Hiding places could be places like caves, under rocks, or in crevices. These will help them to feel secure and less likely to attack.

Add Suitable Tankmates

To keep your Oscar fish from becoming aggressive, it is important to select a compatible tankmate. Some of the best tankmates for Oscars include other peaceful fish, plants, and invertebrates. Some of the best tankmates for Oscars are the following:

  • Birchirs: Bichirs are great tank mates for Oscar fish. They are peaceful and will not harass your Oscar. Bichirs are also very active and love to swim around.
  • Convict cichlid: Many people believe that convict cichlids can be aggressive tank mates, but this is not always the case. Convict cichlids make great tank mates for Oscar fish. This is because Oscar fish are generally timid and do not tolerate other fish very well. However, with a convict cichlid as a tank mate, Oscar fish can feel safe and secure.
  • Firemouth cichlid: Firemouth cichlids are a great tank mate for Oscar fish. They are aggressive and will protect their territory, so make sure you have enough space in your tank.
  • Silver dollar: It seems like tanks with Oscars and Silver Dollar fish get along just fine. Silver Dollar is a great tank mate for Oscar fish because they both enjoy the same types of food, and they are both relatively peaceful fish.
  • Sailfin pleco: Sailfin plecos are peaceful and will not harass Oscar. Sailfin plecos are also very active and will keep Oscar entertained.
  • Jack Dempsey: Oscar fish will accept Jack Dempseys easily. However, it is recommended that a quarantine tank be used for new “acquisitions” of reputedly healthy Oscar fish before introducing them into your main aquarium environment.
  • Green terror cichlids: Green terror cichlids are great tank mates for Oscar fish. They can be aggressive but peaceful most of the time, they both enjoy the same foods, and they make good companions in wide-spaced tanks.
  • Severum cichlids: Oscar fish are known to be very territorial with others, however, they will get along well with banded cichlids. They are both aggressive and share the same behavior but can be peaceful with proper tank maintenance.