The Fish Keeping & Aquarium Guide.

Why Angel Fish Chase Each Other: Understanding Aggressive Behavior in Aquariums

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Angelfish are a popular species of freshwater fish known for their unique and striking appearance. However, some owners may find their angel fish aggressive toward other fish in their tanks.

One common behavior is chasing other angelfish, which can be concerning for owners unsure of the reason behind this behavior.

There are a few reasons why an angel fish may chase other angelfish in their tank. One possible explanation is that the fish establish a pecking order or hierarchy within the tank.

This behavior is often observed in social species of fish, where individuals will compete for resources and dominance.

Another reason may be that the fish are experiencing stress or aggression due to overcrowding or inadequate tank conditions.

Owners need to ensure that their tank is appropriately sized and maintained to prevent these issues from arising.

Understanding why an angel fish is chasing other angelfish is crucial for owners to ensure the health and well-being of their fish.

By identifying the cause of this behavior, owners can take appropriate steps to address the situation and create a peaceful and harmonious environment for all fish in the tank.


Behavioral Reasons

Territorial Behavior


Angelfish can be very territorial, especially when they are in breeding mode.

They may chase other fish away from their preferred location or even attack them. This is especially true for males, who will defend their territory fiercely.

The aggression may sometimes lead to physical fights, resulting in injuries or death.

One way to reduce territorial behavior is to provide plenty of hiding places for the fish. This can include plants, rocks, and other decorations that create nooks and crannies where the fish can retreat.

It is also essential to ensure that the tank is large enough to accommodate all the fish comfortably. Overcrowding can exacerbate territorial behavior and lead to increased aggression.


Mating Behavior


Another reason why angel fish may chase each other is because of mating behavior. During breeding, males will often chase females to mate with them. This can be incredibly intense if more males than females are in the tank.

It is important to ensure a balanced ratio of males to females in the tank to reduce mating behavior. In general, it is best to have two females for every male. It is also essential to provide plenty of hiding places for the females, as they may need to retreat from aggressive males.

In addition, it is essential to ensure that the water conditions are optimal for breeding. This may include adjusting the pH, temperature, and other factors to create an environment conducive to spawning.

Overall, understanding the behavioral reasons behind angel fish chasing each other can help aquarium owners create a more harmonious environment for their fish.

Providing plenty of hiding places and ensuring a balanced ratio of males to females can reduce aggression and promote a healthy, happy tank.


Environmental Reasons

Inadequate Tank Size


One of the most common reasons why angel fish chase other angelfish is due to the inadequate tank size. Angelfish are territorial creatures and require enough space to establish their territory.

When the tank is too small, they become aggressive and chase other fish to establish dominance. A general rule of thumb is to provide at least 20 gallons of water per adult angelfish.


Lack of Hiding Places


Another reason angel fish chase other angelfish is the lack of hiding places. When there are not enough hiding places, the weaker fish have nowhere to escape and are constantly chased by the stronger fish.

Providing enough hiding places, such as plants, rocks, and caves, can help reduce the aggression between angelfish.


Poor Water Quality


Poor water quality can also lead to aggressive behavior in angelfish. When the water is dirty or contains high levels of ammonia or nitrite, it can cause stress and health problems in fish, leading to aggressive behavior.

It is essential to maintain good water quality by performing regular water changes, testing the water parameters, and providing proper filtration.

In summary, environmental factors such as inadequate tank size, lack of hiding places, and poor water quality can contribute to aggressive behavior in angel fish.

By addressing these issues, fish owners can help reduce the aggression between angelfish and create a peaceful and healthy environment for their fish.


Health Issues


When it comes to why an angel fish is chasing other angelfish, health issues could be a potential cause. Two common health issues that could lead to aggression in angel fish are parasites and disease.




Parasites are a common issue in aquariums, and they can cause various problems for fish. In the case of angel fish, parasites can cause irritation and discomfort, leading to aggressive behavior. Some common parasites that affect angel fish include:

  • Ich: A common parasite that causes white spots on the fish’s body.
  • Flukes: A type of parasite that can cause skin irritation and inflammation.
  • Anchor worms: A parasite that can burrow into the fish’s skin and cause irritation.

If you suspect that your angel fish has a parasite, treating it as soon as possible is essential to prevent further complications.




Another potential cause of aggression in angel fish is disease. Just like with parasites, there are a variety of diseases that can affect fish and cause aggressive behavior. Some common diseases that affect angel fish include:

  • Dropsy: A bacterial infection that causes the fish to swell up and have difficulty swimming.
  • Fin rot: A bacterial infection that causes the fish’s fins to deteriorate.
  • Velvet disease is a parasitic infection that causes the fish’s skin to be covered in a velvet-like substance.

If you suspect your angel fish has a disease, it’s important to isolate it from the other fish and treat it as soon as possible.




In conclusion, it is common for angel fish to chase other fish, including other angelfish. This behavior can be attributed to various reasons, including territoriality, mating, and aggression. Understanding the reasons behind this behavior is essential to ensure the fish are healthy and happy in their environment.

Owners of angel fish should ensure that their tank is large enough to accommodate multiple fish and provide hiding spots and territories for each fish. Owners should also monitor their fish’s behavior and remove any aggressive fish from the tank to prevent injuries to other fish.

Overall, understanding the behavior of angel fish is crucial for maintaining a healthy and happy environment for these beautiful creatures. By providing the appropriate environment and monitoring their behavior, owners can ensure that their angel fish thrive in their tank.

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