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How to Stop Fish Aggression in An Aquarium?



How to Stop Fish Aggression in Aquarium

Having an aquarium is not as easy as one thinks. There are a lot of aspects that you should be looking after. Foods and cleaning are the primary things, although the aggression of your fish is also a significant factor that you should be on the lookout for. Several aquarists are unaware of the violence their fishes show and might ignore it as some moderate activity or routine of the fish. Except fish aggression happens for real besides leaving it as it is will result in dire consequences.

Usually, it is not entirely upon their own will as to why they are being the bullies of the aquarium. Some species come with aggressiveness from birth. Sometimes the surroundings and the ecosystem influence the aggressive behavior of your fishes. If not taken care it can reach the point where it becomes uncontrollable.

It is also equally necessary to do a background check before buying certain species to know if they are aggressive or not. Fish aggression will lead to disharmony of your aquarium as well as the submissive or smaller fishes will not live the life you have intended for them.

So, what to do about the aggression? This article will answer all of your questions.

Why do fish show aggression?

There are a lot of reasons why fishes show aggression. The aggression can be for mating or food or territory.

There are a lot of species that are born aggressive. Cichlids, Tiger Barbs, Jack Dempsey are a few fish species with aggressive natures. These species are aggressive and are better far off from the smaller species.

Mating is also an important factor in why the fishes show aggression. When mating season comes around, males will begin hostility towards each other for females. They are not entirely different than any other living being. Males will fight with each other for females to mate.

Such will occur if you have the numbers of males and females unequal in a tank. If there are two males and one female, get ready for a spectacle as the mating season comes around. Usually, males of the same species fight with each other. But do not take any chances and keep the male and female ratio the same.

The territory is a significant aspect of some fish species’ life. Although, not all fishes are territorial. If you have territorial species, they will find a spot in the aquarium and occupy it. But that can lead to aggression if other fishes try to enter its area of comfort.

Like any other living being on the earth, fishes fight for food. The bigger fishes, taking into advantage their size, will intimidate the smaller ones and take all the food. The smaller ones will keep themselves away from harm. The smaller ones will get the leftovers if they are lucky!

Signs of aggression you should look out for

If you have an aquarium, you should look for the signs hinting at aggression. If you notice them, immediately do something about it before anything severe happens.

The most common sign that means aggression is if a fish is chasing after another fish. Sometimes a fish will run after a fish only for a short period. But if a fish is chasing one continuously, then it is bullying.

Also, look for injuries in the smaller fishes. If there are injuries such as a missing scale, damaged fin, etc then your fish are being bullied. The fishes that are being bullied tend to isolate themselves in the most secluded areas of the aquarium and they hang around that area without showing much activity. If any of your fish are alienating themselves in a secluded space then they are being bullied.

So, be sure to look for these signs as your aquarium might not be as peaceful as you think. If you notice any signs remember to act upon them. You can reduce aggression by following the methods mentioned below.

How to Stop the Aggression?

There are some ways that you can follow to reduce the aggression of your fish. It is entirely not possible to put an end to the aggression. Although you can reduce the aggression or stop it for a certain period. Some fishes are naturally aggressive and it is similar to the saying, you can take the animal out of the wild but not the wild out of the animal. The aggression of the natural borns can be reduced although not completely erased.

If you have the luxury of owning another tank you can move the aggressive ones to another tank. Such is the easiest way to remove aggression from your tank. Remove the bullies and give them a space of their own on another tank where they can harm no one and remain alone.

However, if you do not have another tank, go and dig up your aquarium appliances box. Get a breeder box and keep the aggressive fishes separately on the breeder box. Also, known as the ‘time-out’ method. Keep them separately for about a week or so. After releasing them from the breeder box, keep on observing their activities, whether they show more signs of aggression or not. This isolating method might not become successful in reducing aggressiveness all the time but it’s worth a try.

Reorganize and adjust the décor of your aquarium to reduce aggressiveness. Not just reorganizing, you can opt for getting new decorations for your aquariums as well. The alterations on the decorations will reduce the territorial nature of your fishes.

If you have the species that tend to become territorial then you can provide several hiding spaces like caves for them. They will make the hiding spaces their territory, therefore, taking up lesser space for territory.

Also, be careful about the amounts of fish that you will add to your tank. Overcrowding an aquarium is not good at all as none of the fish species will have enough space for themselves. If there is a territorial one among them then it will just be a nightmare. So don’t overcrowd your aquarium and check whether the species that you intend on keeping socialize or not.

Try to keep the number of males and females on a tank equal. As mentioned above males fight with each other to mate with a female. This happens if the number of males and female are unequal.

To avoid the aggressiveness for food all you need to do is spread the food evenly. While you are feeding your fish spread the food all around the tank. In this way, all of your fish will have the opportunity to get their stomach. Concentrating the food in one place will never work as some fishes will only get to eat the food.

If rearranging and breeding box doesn’t work then all you have left is the last option. To take them back to the store. If the aggressive fish won’t stop attacking and dominating others it is better to take the problem away to avoid further problems. Put them in a bag or a container and safely transport them to a store where you brought them from.

Some aggressive fish species

Jack Dempsey


It’s got the boxer’s name so obviously, it is an aggressive one. With a robust body, it is a very territorial one and you should provide them with hiding spots for territories.


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There are a majority of cichlids that tend to be aggressive. Some of the aggressive cichlids are Texas Cichlids, Jewel Cichlids, Peacock Bass, and so on. They are territorial and therefore hiding places are required. Some even tend to take down decorations and plants. So it’s better to keep cichlids on a separate tank.


Oscars are adorned with vibrant colors but they are extremely violent. They can devour smaller fishes. So, keeping them in the same tank as other smaller fishes is a big no. Get them their tanks if possible.

Taking care of your fish is surely not an easy task. Having an aquarium is truly easier said than done. Many things come within keeping an aquarium. Giving your fishes the peace that they require is also as equally important as cleaning and giving food to them. You have to frequently give a glance to your aquarium to get the knowledge of whether they are being aggressive towards others or not. If they are make sure you take care of it.

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