Why do angelfish fight each other?

All animals display specific behaviors according to a situation. It is no different with fish. Whether swimming erratically, locking their mouths, fin nipping, or any other behavior, aggression among angelfish can be worrisome – especially when it takes place in an aquarium.

In this post, we will discuss aggression (fighting) among angelfish, its causes, and what to do to minimize or even avoid such episodes.

Why do angelfish fight each other?

Angelfish are graceful and colourful thus, being a favorite addition to any aquarium affectionate. It’s important to remember that there are differences between marine and freshwater angelfish. 

Freshwater angelfish

Freshwater angelfish, Pterophyllum scalare, are members of the Cichlid family. They are native from South America. Angelfish are the least aggressive fish among the cichlids. Aggression usually stems from protecting their territory and their eggs, which is an uncommon behaviour among fish.

Marine angelfish

Saltwater angelfish are fish of the family Pomacanthidae found in the tropical Atlantic, Indian and western Pacific Oceans living on coral reefs. Marine angelfish tend to be more aggressive than freshwater ones. Male fish are usually more aggressive than females or young ones. 

Why do angelfish fight each other?

In most case scenarios, it is not advantageous for an animal to engage in fights or display aggressive behavior. The reason is very simple: it costs energy! However, aggression may take place when an animal feels threatened or is competing for food, territory, or even possible mates. That’s how hierarchy is established. In the wild, that can be less of a problem given the space available to avoid an unwanted confrontation. This is often not the case in aquariums. Here are some reasons:

  • Small tanks;
  • Hierarchy establishment;
  • Overcrowding;
  • Spawning and breeding.

Even though some angelfish owners have not had any problems with their fish, that doesn’t mean there will never be a fight between them. So, it is important to pay attention to your angelfish behavior – what prompts them to fight, and how to spot those triggers. Here are some of the causes that lead them to fight:

Small tanks

Angelfish are territorial, so if you have a small aquarium with more than one fish chances are your angelfish will fight with another one (or even other species) to secure their resources. Make sure your tank is big enough to avoid this situation and that it has various hiding spots that they can use. 

Also, when buying a tank consider the final size of your fish, whether it’ll be a community tank or not, and if so, how many fish you will have in it. The ideal tank size for an adult angelfish is 22-gallons (83.3 L) and a minimum of 12-gallons (45.4 L) for every extra angelfish. 

Another thing to pay attention to is whether they are fighting or just chasing each other for fun. If you see that one of your fish has fin nipping marks, it’s time to separate them.

 Hierarchy establishment

In a group of angelfish, there’ll always be a pecking order in which the strongest will become the leader. After that, the fight subsides. There’re cases where regardless of the hierarchy being established, conflicts still take place. The leader becomes a bully and we need to figure if there is something else inciting such behavior. 


As mentioned before, angelfish are territorial. If you address the issue of a small aquarium but overcrowd it with various angelfish, you’ll still have a problem with competition for food, and territory. These problems are usually ‘solved’ with fighting.  Stress can also lead to combative behavior. A number of 5 angelfish is ideal to hinder aggressive or bully behaviour.

Limited food and aggressive temperament

When angelfish are underfed or not fed at all, they’ll fight to secure their resources. In this case, food. Such events can happen outside feeding time. You can assume that bullying is taking place especially during mealtimes. The bullied fish tends to isolate themselves from the others during meals or even retreat to its hiding spots when the bully is seen. 

Spawning and breeding

Contrary to many species, freshwater angelfish are very protective of their nest and take care of their eggs until they become fry. So, if angelfish sees that their offspring are being attacked, they will fight to protect them. 

However, they have a tendency of displaying some aggressive behavior when spawning.  If after the fight they calm down and swim together for a while, chances are they were mating. If the attack happens after the spawning, they have probably eaten their eggs.

Mating or fighting – how to distinguish between them?

Sometimes, the mating ritual for angelfish can be mistaken for bullying or fighting. But there are differences between mating and fighting. How can we tell them apart?

Signs of mating in angelfish

  • Female angelfish gets more aggressive and her belly enlarges;
  • Males chase the females around the tank;
  • Male and female angelfish locking lips while twisting around;
  • Grooming each other as well as flashing their fins.

Once the courtship is finished, the male and female angelfish will start to clean the chosen spot in the aquarium as their mating site. The female angelfish will lay her eggs there.

Signs of fighting in angelfish

  • Locking lips;
  • Chasing each other around the tank;
  • Hitting each other with their tails; 
  • Staring each other down;
  • Nipping each other’s fins.

If you witness such behavior, you must separate your fish. You can either remove the angelfish to different tanks or you can attach a divider in your aquarium to minimize their aggressiveness by limiting their contact. This divider can also be efficient to separate aggressive angelfish during breeding or raising fry.

Decreasing aggressiveness among angelfish by changing their environment

Since angelfish are territorial, a change of environment might just be what they need to chill out. When you change their environment, especially the one where they dominate, changing the layout of the aquarium will give them time to explore their ‘new’ home. Some precautions are needed though.

Changing the aquarium layout

Before changing the layout of the tank, make sure you remove the aggressive fish from the aquarium for a few days and monitor the behavior of the remaining fish.  When the fish are calmer, reintroduce the aggressive one and keep an eye on their behavior pattern. When you change the layout of your aquarium, the dominant angelfish will no longer recognize its territory and all fish will be at the same hierarchical level. If you didn’t see an improvement, try to remove the other aggressive fish and so forth, until you sort the fighting issue.

Go green

Take advantage of plants to provide your docile angelfish a hideaway from their bullies. Besides plants, decorations such as caves, and castles are also a good option. Aggression episodes last as long as the aggressor and the aggressee are in the same location. Having hiding spots in your tank will give your targeted angelfish places to rest and be safe as well as give the aggressors some time to calm down. 

Friendly distraction

A good way to divert aggression is to distract the aggressor. When you add smaller schooling fish in the aquarium, you give your angelfish something to concentrate on other than the bullied angelfish. Adding similar size or larger fish with calm or even semi-aggressive behavior is good to minimize the aggression levels of your angelfish. Keep in mind that once you add smaller fish to the aquarium, there is a chance they might become an angelfish snack.

Let it mellow… but not completely

Angelfish hierarchy is determined after a fight in which the ‘winner’ secures its place as the leader of the school. But this is not the only way they reinforce their social status. These fish also excrete chemical signals contained in their bile and urine in the water to show hierarchy.

When we renew the water in the aquarium, these chemical signals get diluted which can increase aggressiveness levels among angelfish. A study monitored the relationship between the volume of water renewed in the tank with the frequency of fights among freshwater angelfish. The research concluded that when a smaller volume of water is changed, the aggressive behaviour of angelfish subsided after 1 hour.

Tips for preventing your angelfish to fight each other

Here’s a checklist of all that was discussed in the post. If you pay attention to this list, the chances of your angelfish fighting each other will be reduced. Most importantly, they will happily share the same tank.

  1. Keep your angelfish in a big aquarium: a minimum of 22-gallon (83.3 L) tank with an additional 12-gallons (45.4 L) per extra angelfish;
  2. If you are going to have more than one angelfish, make sure they are in a mixed group of five;
  3. Mealtime: feed them enough food to avoid competition. Do not overfeed them;
  4. Know the difference between a fight and a mating ritual;
  5. Separate the breeding pair from the remaining fish until their eggs become fry;
  6. Remove the bully: isolate the aggressor for a few days;
  7. Change the layout of the aquarium and add some foliage before reintroducing the aggressive fish;
  8. Add new tankmates for distraction;
  9. Remove any fish that is either sick or harmed from the aquarium. Give your fish a fair chance to recover before releasing it back to the tank;
  10.  Change small volumes of the water from your tank.


Angelfish have a semi-aggressive behavior that makes them prone to fight. Having said that, they are the most peaceful among the cichlids. They can get along with each other and other fish species when in a large community tank. However, it is important to observe your fish closely to address any aggressiveness issue. 

Good starting points are to understand their hierarchical structure, as well as their physical and environmental needs. A big tank with plenty of distractions (but not too many), regular meals, other tank mates, and not changing the whole volume of water from the tank might do the trick. It’s all about reducing their level of stress.

Also, it’s important to distinguish between fighting and mating behavior. If your angels show no signs of damage, or after what you might consider as an aggressive behavior they swim along with each other, it could be a mating ritual. But have a spare tank, just in case.

Angelfish are beautiful fish and a hobbyist favorite. They can display some aggressiveness towards each other and even other fishes depending on the circumstances. In this post, we have explained some of the situations which might trigger this behavior and tips on how to avoid them. Thus, you will have calmer and happier fish.

Have you witnessed any fight between your angelfish? How did you avoid the fight? If you have other questions or comments, leave us a message below. 


Gauy, A. C.S.; Boscolo, C. N. P.; Gonçalves de Freitas, E. (2018). Less water renewal reduces effects on social aggression of the cichlid Pterophyllum scalare.  Applied Animal Behaviour Science, 128, p. 121-126.

Gómez-Laplaza, L. M. & Morgan, E. (1993). Social isolation, aggression, and dominance in attacks in juvenile angelfish, Pterophyllum scalare. Aggressive Behavior, 19(3), 213-222. DOI:10.1002/1098-2337(1993)19:3<213::aid-ab2480190306>3.0.co;2-X

Moyer, J. T. and Nakazono, A. (1978). Population structure, reproductive behavior and protogynous hermaphroditism in the angelfish. Centropyge interruptus at Miyake-jima, Japan. Japanese Journal of Ichthyology, 8 (1): 25-39.