Are Goldfish Aggressive? And How To Reduce Aggression?

Goldfish have been the most domesticated species of fish. But can they be aggressive? Many Goldfish keepers ask this question at some point. If your Goldfish has been acting aggressively for some time, you may not know what has been causing it. In this article, I will explain the many different reasons why your Goldfish may be acting more aggressively than usual, and how you can take care of the situation.

Goldfish are friendly and peaceful fish. They are very pleased with their tank mates. Although if they face any problem, if they don’t like their environment, their food, or the tank is too overcrowded then they Behave aggressively.

If one or some of your Goldfish have been aggressive lately, there is surely a reason behind it. By the end of this article, you will surely be able to identify the reason behind the sudden aggressiveness of your Goldfish, and how you may fix it.

Table of Contents

Why do Goldfish become Aggressive?

How can such a peaceful species of fish become so aggressive? There are many possible explanations for this sudden change in attitude, which are as follows:

Food: It is quite possible that your Goldfish are competing for food, which ignites aggression among some. This can be due to less food being available to your Goldfish or if the food is not distributed in the tank properly.

Overcrowded: Goldfish enjoy a lot of space and if there are a lot of fish taking up the space around them, they may become aggressive toward those fish. This is only natural, and it is best that Goldfish be kept in larger tanks with fewer fish around them.

Bad Water Quality: Imagine not having the right air to breathe in. This will most certainly cause aggression in us. The same goes for Goldfish. If the water conditions, such as the temperature, pH, oxygen, and nitrite levels are not optimal for your Goldfish to live in, your Goldfish will become aggressive and even sick.

Territorial: Some Goldfish can feel territorial towards the place they have been living in and will not tolerate new tank mates. The Goldfish will think of the new tank mates as a potential threat to their own personal space and will attack them to get rid of them. Generally, Goldfish are not very hostile towards new mates, but if you add new fish after a very long time, it may be hard for your Goldfish to accept the new mates.

Sick Fish: If one of your fish or Goldfish in the fish tank is sick or is dying, your Goldfish will find their duty to get rid of that fish. They will chase the sick fish as the sick fish will be slower and tired. One or all of your Goldfish may become aggressive towards one sick fish. This can be a good indicator for you to tell if one of your fish is sick.

Slow and Fast Swimmers: Some Goldfish are known to swim faster than other species and types of Goldfish. This will cause the faster Goldfish to chase the slower ones. This can just be a form of sport for the Goldfish, or in some instances, this may even be harmful to the slower fish.

Unusual Features: Bullying is very common among Goldfish, and they will most certainly chase fish that look different from them. Some fish have large fins and tails that might be something that your Goldfish have not seen before. This causes them to chase the different-looking fish out in simple curiosity, which may come off as aggressiveness.

Mating: When the spawning season is at its peak, male Goldfish tend to chase around female Goldfish, in an attempt to mate. This may come off as aggressive behavior, while the males are only trying to mate. This should not be worrying you if you wish for your Goldfish to mate.

The ratio of Males to Females: If the ratio of male Goldfish to female Goldfish is high, this causes hostility among the Goldfish. Male Goldfish are known to harass female Goldfish in an attempt to mate, which causes the female Goldfish to become scared and hide.

Personality: some Goldfish are just a little aggressive in nature, unlike an average Goldfish. This is something that cannot be fixed and the only way to know whether your Goldfish is aggressive in nature or not is to allow it to live with the other Goldfish for a while, under ideal conditions.

External Disturbances: Goldfish can easily be disturbed by someone tapping on their tank or scaring them around. This is very common with children keeping an aquarium, as they tap on the Goldfish tanks just to startle them. This can in turn cause your Goldfish to become aggressive and hostile toward each other.

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Is your Goldfish Aggressive or just playing around?

It may be easier than you think to tell simple playing and hostility apart. But here are some signs for you to spot aggression in your Goldfish:

Chasing Around: If your Goldfish are chasing each other around, pay closer attention to which one is actually chasing the other around. The Goldfish that is constantly chasing the others around is the aggressive one.

Injured Fish: If one of your fish or Goldfish has become injured and there has not been any incident that may have caused it, it is quite possible that you and the aggressive Goldfish are in the tank. You may not have witnessed it happening, but the aggressive Goldfish may have injured the fish in question. The injured fish is now more at stake so you must take care of it. You must make sure to remove the injured fish for it to heal in isolation until you figure out which one is the aggressive Goldfish.

Hiding Fish: If you observe that some of your fish or Goldfish are hiding under plants or rocks in their tank, you may have an aggressive Goldfish in the tank. The other fish will try to escape the aggressive Goldfish by hiding around in places.

Dead Fish: Suddenly, if one of the fish in your Goldfish tank drops dead, it may be caused by an aggressive Goldfish. if the dead fish was not sick or unwell recently and dies for no apparent reason, you most certainly have a hostile Goldfish in the tank.

How to take care of your aggressive Goldfish?

If you have an aggressive Goldfish in your Goldfish tank, you must take quick measures to fix the problem, or your other fish in the tank will be at risk. Here is how you can take care of this issue:

Tank Dividers: This is an easy fix and will cost you almost nothing. You can simply buy an acrylic tank divider from the local pet store which will keep your aggressive Goldfish separate from the other tank mates. Make sure to buy an acrylic tank divider, as it is inert and will not react with any of the water substances or be harmful to your Goldfish in any way.

Hiding Places: To protect your other fish from the aggressive Goldfish, you can add plantation and decorative rocks. These will not just add to the aesthetic views of your Goldfish tank but will also provide ample space for your fish to hide from the aggressive Goldfish.

Feeding: One reason why your Goldfish are becoming aggressive is that they are not being fed well. To fix this, you may separate your Goldfish when you are feeding them so that each one of them gets enough food and they do not have to compete for food with each other. Make sure to feed your Goldfish properly in adequate portions, 2 to 3 times a day. To ensure equal distribution of food, you may try to spread the food evenly all over the water when adding it to the tank instead of adding it in just one place.

Isolation: If one of your Goldfish has become aggressive, it is best to separate it and keep it in a completely separate tank. This will, however, double your duties, but will keep your other fish safe from the aggression of the hostile Goldfish. After some time, the aggressive Goldfish may become less aggressive and friendly enough to add it back to the main tank. If the Goldfish in question is still hostile after isolation, it is best for you to keep it separate permanently.

Floating Box: Another way is to isolate the aggressive Goldfish within the tank, by adding a floating box. This will also keep them connected to the tank environment and will also keep them separate from the rest of the fish.

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How to prevent aggression in Goldfish?

It is possible that, unknowingly, you may be causing aggression in your Goldfish. Here are some tips that you can follow to prevent aggression in your Goldfish altogether:

Less Crowded: You must always provide a large space for your Goldfish. A single Goldfish requires at least 20 gallons of water for itself. For every added Goldfish, you must add another 10 gallons of water and space. You must make sure that the personal space for your Goldfish is not being taken up by a lot of other fish.

Water Quality: You must ensure that you are doing regular water changes so that the water that your Goldfish is living in stays clean and healthy. To maintain the water quality, you may add live plants to your Goldfish tank, which will also maintain the oxygen and nitrate levels. You must keep a regular check on the temperature and pH levels of the water in your Goldfish tank. Adding a heater will maintain the water temperature as per your Goldfish’s requirements. If the water quality of the Goldfish tank is good, your Goldfish will stay happy and will be less likely to become aggressive.

Isolation in Mating Season: If you do not wish for your Goldfish to mate and wish to prevent unnecessary aggression towards the female Goldfish or the male Goldfish, you may want to separate the two during the mating seasons.

Adequate Food: Make sure to feed your Goldfish enough food so that they do not compete for food. But do not overfeed as this may cause them to become sick.

Healthy Male to Female Ratio: Too many male Goldfish will chase around the lesser in number, female Goldfish. So, make sure that when keeping Goldfish, you keep an equal or close to an equal ratio of male to female Goldfish. The ideal ratio is 3 males to 2 females.

Add New Fish Slowly: When adding new fish to the Goldfish tank, you may want to proceed with caution. Add the new fish one by one, to allow the Goldfish to adjust to the new tank mates, instead of the Goldfish feeling territorial and harming the new fish.

Add New Fish at Proper Time: Goldfish can become territorial when they have lived in a place for a long time. If you wish to add more fish to your Goldfish tank, you must do so within the first 7 weeks of adding the Goldfish. If you add new tank mates any later than this, your Goldfish would have assumed that the tank only belongs to them and will become aggressive and territorial when new tank mates are added.

Keep Peaceful Fish: To encourage a more peaceful and less hostile environment in the Goldfish tank, you may want to add some rather peaceful species of fish to the tank. Some of the known peaceful fish species are zebra danios and rosy barbs. These species also go along with the Goldfish. Make sure that you do not add naturally aggressive fish species to your Goldfish tank, as they are certain to cause hostility among the Goldfish as well.

The Bottom Line on Are Goldfish Aggressive?

To say that Goldfish are generally a peaceful species of fish, would not be wrong. As with me and you, some things can trigger Goldfish to act aggressively and will create a hostile tank environment. But once the issue has been fixed, you will notice your Goldfish return to normal in no time. Make sure to keep your Goldfish happy, as their aggression can be extremely dangerous for the rest of the tank mates. But when happy, Goldfish are the most loving and easy-going species of fish that you will ever find.