Are Goldfish Aggressive? (And How To Reduce Aggression)

If you’re wondering, “are goldfish aggressive?” then you’ve come to the right article. Not only are you going to find out whether goldfish are aggressive or not, but you’ll also learn what causes aggression, how you can prevent aggression, how to know if a fish is a victim of aggression, and much more.

So keep reading to find out everything you want to know about aggression in goldfish!

Are Goldfish Aggressive?

So to answer the question: Goldfish are generally peaceful fish. When aggression does occur, it’s due to problems in the tank or with other tank mates. But for the most part, you should have no problem adding them to a tank with other fish.

However, one caveat to that is when you keep them with smaller fish. If a goldfish is around smaller fish, then there’s an increased chance that they may bully them (or, if they can fit in their mouth, eat them).

Are Goldfish Territorial?

You may be wondering also if goldfish are territorial. When a fish is territorial, it’s much more likely that they’ll try to act aggressively to protect their space. Fortunately, as long as the tank is big enough, your goldfish shouldn’t be territorial and should remain friendly with the other fish.

With that being said, though, for best results, you should try adding all your goldfish within a short period of time (but not too short the tank can’t handle it). Generally, 6 weeks is a good amount of time.

This is going to reduce the chances of them taking an area of the tank as their own territory.

Why Does Aggression Occur In Goldfish

Now you know that it’s pretty rare for aggression to occur in goldfish. However, that doesn’t mean it never happens. And finding out the cause of aggression in goldfish is going to help you come up with a solution to stop it!

Competing For Food

One of the most common causes of aggression in goldfish is competing for food. Goldfish (like all fish) are extremely gutty. If they see other fish trying to eat their food, then they may see it as a threat and try to ward them off.

The easiest way to tell if this is the aggression you’re dealing with is when it’s only occurring during feeding time. But fortunately, as you’ll find out later, there are plenty of ways you can stop this aggression from happening.

When They’re Mating

During mating, the chances of aggression are also going to increase. The male fish is going to act aggressively towards any other competitors, and it may even look like they’re being aggressive towards the females as well.

Mating aggression is far more likely to occur after certain criteria have been met in the tank. For example, you’ve been feeding them more, or the temperature in the tank has risen to the perfect breeding temperature for them. (68-74°F)

And sometimes, even a large enough water change can trigger mating behavior in your goldfish. Whatever the case, if you look at your male goldfish, you’ll notice that they’ll have breeding stars on their gills and front fins. This is the tell-tale sign that they’re ready to breed.

Slow Swimmer And Fast Swimmers Are In The Same Tank

Sometimes when you put slow swimmers and fast swimmers in the same tank, aggression breaks out. When you’re deciding what goldfish to buy, you need to remember there are two different body types. One type has a streamlined body, while the other is more egg-shaped.

While there’s normally no problem adding these fish together in a tank, sometimes the faster swimmers will pick on the slow swimmers, nipping their tails and any other soft spots on their bodies.

Some fish that will often get bullied more are fish that have long-flowing fins, body parts that stick out more than they should, and of course, bulbous bodies.

The Tank Is Overcrowded

This is another one of the most common causes of aggression in goldfish. Most people don’t realize how much space goldfish need and often end up placing too many fish together in a tank that isn’t nearly big enough for them.

To put it in perspective, it’s recommended that your tank be at least 3 feet long so your fish have enough horizontal swim space. As well as this, there should be 20 gallons for the first goldfish you keep and then an additional 10 gallons for each new goldfish.

As you can see, this is a lot of space, and if you don’t have it, it’s going to increase the chance of aggression in goldfish.

A Fish Is Sick

This isn’t a unique reason for goldfish, but actually a common reason for all fish.

If your goldfish is turning black, however, it can be a symptom of something else entirely. Read about it here! When one fish is sick, the others will begin attacking, bullying, or even killing them. While it’s not known for sure why this happens, there is a general consensus.

It’s believed that the healthy fish see the sick fish as a threat. Not just because they may attract predators but also the risk of passing on the sickness. So, they try to ostracise them from the group to increase their own chances of survivability.

While nature is cruel, it’s the best way to keep the majority of the fish in a shoal alive.

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Sometimes, it’s nothing more than your goldfish’s personality. They may just naturally be aggressive, and there’s not much you can do about it. It will normally be the ‘alpha’ male or ‘alpha’ female that displays these aggressive tendencies.

If you notice they’re getting too out of hand, then the only real solution is to move them to another tank. However, if this puts you off goldfish, just remember this can happen with any species of fish, no matter how peaceful the majority of them are.

They’re Territorial

Sometimes goldfish are going to be aggressive when they’re territorial. While this isn’t as common in this species of fish, it does definitely still happen. It normally happens the most when new fish are introduced to the tank with them.

It’s much more likely to happen if the goldfish in the tank already have an established hierarchy and in the early days of introducing a new fish. However, after about a month, it should simmer down.

There Are Too Many Males

If you have too many males and not enough females, then this is often going to cause aggression in your fish tank. While this won’t be like other forms of aggression, it’s still going to end up causing females to get harassed a lot.

As well as this, the males may also begin to fight each other, which ultimately may end up causing one of them to become seriously injured. So when you’re stocking your tank, make sure you’re adding the right mix of females and males.

(Find out whether goldfish can live with glofish, mollies, minnows, shrimp, or guppies.)

How Can You Tell When Aggression Is Occurring?

If aggression is occurring in your tank, there are a number of ways you’ll be able to spot it. Here are some of the most common ways to know that aggression is happening.

One Of The Fish Is Injured

One of the most common signs that aggression is occurring in the tank is when one or more of the fish in the tank are injured. Most of the time, these injuries will be on their fins and tail; however, any of their body can be injured.

Just make sure the injury is being caused by another tank mate and not a sharp object in the tank or a disease.

You Notice The Aggression Happening

Of course, this is THE biggest indicator of aggression. And that’s when you can actually see it occurring. When you can see aggression occurring in your tank, then there’s nothing else to say on the point.

The only next step is to figure out why it’s happening and the best course of action to stop it.

Fish Are Hiding

You may also notice fish that are getting bullied in the tank begin hiding a lot more. They may hide behind any ornament or plant that you have in your tank or try to find a corner to put their back up to.

However, just because your goldfish is hiding doesn’t necessarily mean that they’re being bullied. They also hide when they feel unsafe (such as in a new tank) or if they’re sick.

A Dead Fish

One of the clearest signs of bullying, especially when other signs have already been seen, is a dead fish, ESPECIALLY if the fish has injuries.

If you notice a dead fish in the tank, then you’ll need to find out exactly which fish is being aggressive and remove them from the tank.

(As well as fighting, it could also be caused by diseases such as swim bladder disease, dropsy, fin rot, popeye, or ich.)

How To Tell If It’s Bullying Or Not

It can be easy to mistake goldfish interacting with each other as bullying. If you’re not sure whether they’re bullying each other or not, fortunately, there are a few common signs.

The signs to look for include:

  • Swimming around each other instead of after each other or into each other.
  • You may also notice that your goldfish meet and then dart away from each other. Instead of one goldfish chasing the other.

What Should You Do When You Notice Aggression In Your Tank?

Fortunately, if one of your goldfish is being aggressive, there are plenty of things you can do to curb the aggression and make sure all your fish are happy. Here are some quick tips.

Make Sure The Tank Is Big Enough

First of all, you’re going to want to make sure that your tank is big enough for all the goldfish you’re keeping. If the tank is overcrowded, then the other steps may not work at all.

Remember, your first goldfish will need 20 gallons by themselves, and each additional goldfish will need another 10.

Isolate The Bully

You can also try removing the bully from the tank and putting them somewhere else. If that fails, you can also use a tank divider so they can’t get to the other fish.

Even removing them for a certain amount of time can sometimes stop them from acting aggressively. This is especially true if they see one area of the tank as their territory or if they think they’re the alpha fish.

It’s also a great idea to move the tank around before you add them back. When you move the tank around, they’re going to feel like they’re in brand new territory and be much less likely to act aggressively.

Separate The Aggressor During Feeding Time

If one of your fish is only aggressive during feeding time, then it can be a good idea to separate them from the rest of the fish. You can do this by either putting them in a floating box or catching them in a large net.

Once they’re safe inside the net, you can begin feeding them and the other fish without worrying about aggression occurring.

Failing that, you can always try spreading the food out over the tank to make sure they’re all getting an equal amount.

This is also a good time to make sure that you’re feeding your goldfish enough food throughout the day. After all, of course, they’re going to act aggressively around food if they’re not getting enough.

You should be feeding your goldfish 2-3 times a day for 2 minutes. Anything that isn’t eaten in that time should be removed from the tank.

Ensure The Water Quality Is Good

When the water quality in your tank isn’t good, it’s going to stress out all the fish in your tank. When they’re stressed, it’s a lot more likely that they will act aggressively towards each other.

Some ways to make sure the water quality is good to include making sure you’re using a filter, performing water changes regularly, and removing any waste or debris that builds up in the tank.

Add Plants And Hiding Places

Another great way to reduce aggression from occurring is to add plants and hiding places to the tank. By doing this, you’re going to not only give any more docile fish a place to hide, but you’ll also provide plenty of areas that will block the line of sight f the aggressors, reducing the chance that they’ll chase.

Avoid More Commonly Known Aggressive Goldfish

You could also try to avoid goldfish that are commonly known to be a little bit more aggressive. Bubbly-eyes and ryukins are an example of this. However, if you really like the look of them, then you shouldn’t be put off too much, as most of the time they’re going to be completely fine.

Add Other Peaceful Tank Mates

Lastly, it’s also a great idea to add other peaceful tank mates into your tank as well. This is going to reduce the chance of aggression happening from your goldfish.

If you’re not sure what tank mates to get, then some great choices include rosy barbs, white cloud minnows, and zebra danios. If you don’t want any more fish, you could also try adding more shrimp and snails.


Now you know everything there is to know about goldfish aggression. While aggression is rare when it doesn’t happen, there’s normally a problem that’s causing it, such as a tank that’s overstocked or your goldfish not getting enough food.

There are also plenty of things you can do to stop aggression from occurring, such as making sure the tank is big enough, that you’ve added lots of hiding places, and that you’re adding peaceful fish into the tank as well.

About the author

Hey there! I'm Antonio, the passionate owner and chief editor of Betta Care Fish Guide. With over half a decade of hands-on experience, I've become your go-to expert for all things betta and tropical fish.

Over the past 5 years, I've not only kept bettas and other tropical fish but also connected with a diverse network of hobbyists, seasoned fishkeepers, and even veterinarians.

Now, I want to help other beginner fish keepers who had the same questions as me when they were just starting out! So they can save themselves a ton of time and keep their fish happy and healthy!