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7 Causes of Aggressive Goldfish Behavior & How to Stop It

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By Lindsey Stanton

Goldfish in aquarium with green plants

Have you ever wondered “Are goldfish aggressive?” or “Why is my goldfish pushing my other fish around?”

I get it. It can be stressful! So, if you’re frustrated trying to maintain the peace in your aquarium, you’re in the right place. Today we’re going to talk about the causes for this behavior and what you can do about it.

Let’s jump in!

Are Goldfish Aggressive?

Not usually. As a general rule, goldfish are very gentle-natured, peaceful fish. They get along well with just about everyone. Even fish and creatures of other species. They are probably one of the most peaceful aquarium fish you can keep! So, it’s pretty safe to say, they definitely don’t cause problems under normal circumstances (most of the time).

That said, in some cases, they can be little STINKERS!

Reasons Your Goldfish Could Be Aggressive

ryukin goldfish
Image Credit: slowmotiongli, Shutterstock

When it happens, it’s important to recognize why so you can get to the root of the problem.

What does it look like? Aggressive goldfish typically pursue another goldfish (from behind) around the tank, pushing or jostling them. Sometimes the two may push at each other, swimming in circles or chasing one another around. In worse cases, fin damage can happen from nipping or other injuries can occur if one fish is pushed into a hard object or is being excessively pursued.

Unfortunately, yelling “BREAK IT UP, KIDS!!” to distract them doesn’t ever seem to work too well.

Or banging on the glass.

Or chasing with a net.

The first step? Determine WHY the fish are acting this way.

The 7 Causes of Aggressive Goldfish Behavior (How to Stop It)

1. Feeding Jealousy


Goldfish with a white tail_Nastya Sokolova_shutterstock
Credit: Nastya Sokolova, Shutterstock

This is more common than you’d think.

The way you determine if it is feeding jealousy behavior is that you’ll notice they only (typically) start this behavior at mealtimes. It’s also not typically as fast-paced as mating behavior.

Sometimes both will fight after they fill their mouths. Sometimes just one thinks the other got their grub. Each wants what the other one has.

Greedy little pigs, right?!

How can you deal with this?

Good news:

This isn’t usually severe enough to warrant intervention on your part and rarely leads to damage of any kind.

But if it really bothers you or if this behavior bleeds in to a good part of the rest of the day (such as whenever they think you are going to feed them), here are some things you can try.

  • You can try using a tank divider. This does not allow the fish to have contact with each other and will 100% stop all fighting.
  • You could also try separating them just at mealtimes with a floating basket or other in-tank separation device… but this can cause more stress than just letting things be (not to mention being way more work for you).
  • Offering lots of hiding spots through the addition of live plant vegetation can help give bullied fish a place to rest.

2. Spawning


eggfish goldfish_seaonweb_shutterstock
Credit: seaonweb, Shutterstock

Ah, when love is in the air (or water), you might think it’s actually WAR. Spawning goldfish can be insanely hostile. I don’t think it gets meaner among our goldies than when this is happening!

The way to distinguish spawning aggression from other aggressive behavior is to first see if you can spot the fish’s genders. Males will usually have breeding stars on their gills and front fins and they will be the ones doing the pushing. Females will be swimming for their lives!

This is usually triggered after a large water change, full moon, spring weather, weather front or have been feeding more (or sometimes a combo of all of those). Sometimes whole tanks or ponds will be participating all at once, which is a site to see! Slim-bodied pond fish look like lightning as they zip around in the pursuit. Fancy goldfish often go about this in “slow motion.”

If things are getting too rough and the females are getting overly stressed you may need to intervene to protect them.

Read More: How to Breed Goldfish

3. Sickness

vet holding goldfish
Image credit: BannokStockPhoto, Shutterstock

One thing about goldfish is they don’t always show a lot of compassion. When one is sickly or weak, sometimes the others make the situation worse for it and start attacking or pecking on it. Sad, but it happens. This is why I usually advise removing a sick fish from the aquarium to a hospital tank if possible. Such behavior can really compound the stress and make it difficult for them to recover.

Why do they do this?

I don’t know for sure, but I speculate that it seems to be nature’s way of eliminating the sickly ones from a population. A fish that’s harboring disease is more likely to infect others and poses a threat. By trying to pick them off, healthy goldfish could be trying to protect themselves and the others.

If you suspect your fish is sick and want to ensure you provide the right treatment, we recommend that you check out our best-selling and comprehensive book The Truth About Goldfish on Amazon today.

The Truth About Goldfish New Edition

It has entire chapters dedicated to in-depth diagnoses, treatment options, a treatment index, and a list of everything in our fishkeeping medicine cabinet, natural and commercial (and more!)

4. Territorial

common goldfish
Image Credit: vu dinh quoc an, Shutterstock

This usually happens as a result of introducing a new fish to the tank with a fish that’s been living there for a while first. A fish that’s had it’s home all to itself may not be happy with a new invader in its space, so they try to show them who’s boss. 

The good news?

This can often be avoided by introducing your new fish friend properly. It may or may not settle down over the course of a few months. (For me, it generally is over after 4–8 weeks.)

Also, in my experience, it seems more likely you can have chronic problems with this if your tank lacks a well-established “hierarchy” or there are only two fish.

5. Personality

lionhead goldfish swimming
Image credit: Huy Thoai, Shutterstock

You know, I hate to overly humanize fish, but sometimes you get one that’s just bratty. It might not any of the above problems, it’s just that you’ve got a fish with a more pushy personality. They may bully the others and they won’t get along.

And there seems to be no rhyme or reason.

It may or may not be cause for concern, depending on just how aggressive of a goldfish you’ve got on your hands. Having a “pack leader” that displays alpha characteristics might be normal. But if you can tell it causes a lot of stress on the others and causing constant disturbance to your tank, might be time to think about relocating such a fish?

6. Higher Stocking Densities

goldfish in tank with marbles substrate
Image credit: Pixabay


Sometimes fish that are kept in more crowded conditions for a longer time may be more prone to picking on each other, in my experience anyway.

Now, it doesn’t always happen this way. There are plenty of people who keep very heavily stocked goldfish aquariums with no problem whatsoever. Maybe it has something to do with a little social hierarchy being more established.

Maybe their fish have more calm personalities.

Maybe they’re all siblings.

But if you suspect higher stocking densities is contributing to more tension in the water, sometimes having more “elbow room” helps the fish feel more comfortable enough to stop this behavior.

7. Body Characteristics

Goldfish in aquarium
Image By: dien, Shutterstock


Fancy goldfish can be prone to getting picked on due to their unusual features that have come from hybridization. Long fins and wens can be targets. Fin nipping can be a real problem, especially with fish that have longer fins.

Fish that have been bred to have overly long, trailing fins may have problems with other fish munching on them – especially if they drag on things and sustain injuries, causing excess slime or damage. Sometimes goldfish will take a liking for another fish’s wen and totally mow it off.

Sounds weird, doesn’t it? But it can happen, though thankfully not very often.


How to Deal with Aggressive Fish Behavior

  • Use a floating box to isolate bullies. Sometimes they calm down after being released from “time-out.” Also useful during feeding time.
  • Use a tank divider if the problem persists long-term after temporary separation
  • Consider supplying your fish with more swimming space if cramped conditions are the root cause
  • Watch the fish carefully for signs of stress

wave tropical divider


I hope this has helped you decode aggressive goldfish behavior. Want to share your experience? Have a question?

Drop me a line below!

Featured Image Credit: dien, Shutterstock

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