Stop a Fish from Chasing Its Tank Mates | Aquarium Care

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Fish have been dubbed to be the most aggressive things on this planet next to people, so it's pretty common that you'll find one fish chasing another fish. The thing is, is it chasing it to the point where it's shredding its fins, it's kicking up at the corner, because this will surely result in the fish probably dying.

If one fish is chasing the other fish, and the tank is big enough, the fish are typically compatible, one thing you can do is to let them re-establish their territories by changing the tank decorations. Typically when you add a new fish to a tank the existing fish that are in there are going to be very territorial and not want to see anything new in the tank.

So, for that reason, I recommend changing the tank decorations. Not physically changing them, but just moving them around, creating new caves, new hiding places, whenever you add a new fish to the tank. That will disorient the existing fish and make them re-establish new territories including or incorporating the new fish as part of its new environment so it's less prone to chase the new fish.

If you try this and it's still not working you could try pulling out the aggressor leaving them in a bucket with an aerator and a heater for six to eight hours. That should disorient them so when you put them in the tank sometimes they just happen to click in and get along with their existing tank mate. Or if you have the luxury of setting up another aquarium you can move the aggressor out into the other aquarium for a few days to a week, let the new fish get acclimated, let it start eating, let it develop territories, and then put the old fish in.

One way to prevent fish from fighting with each other is to purchase fish with this in mind. So remember, fish are aggressive, so they're going to pick on things that are the same size or smaller. If the new fish is slightly larger then it has a much better chance defending itself. Very rarely will you put a new fish in the tank and that new fish starts chasing all the existing fish. It's usually the other way around. So I recommend buying fish that are slightly larger than the fish that you already have so they can hold their own in the tank.

You could also try introducing the fish at night or shutting the lights off in the tank, shutting off the lights in the room, and introducing the fish when everyone's asleep. So they wake up the next day and all of the sudden there's a new fish in the tank. That'll disorient them and sometimes allow the new tank mate to be part of the new day, the new environment.

All these things can be done with success.

[ashantizulu]

Lol😂.. imagine me laying there in my bed sound asleep ..I wake up turn on the lights & there’s some human staring at me yawning, stretching, wiping their eyes & says “GOOD MORNT, Ning” 😂😂😂

[abdulquddus]

Thanks a lot for the video. Keeping aggressive fish seperate for 6-8 hours and putting back helped stop chasing other fishes. It's twice now it worked for me.

[SeNniN]

my guppy is aggressive. hes the smallest one and started bullying everyone. im going to have to give him some alone time.

[damiantorres]

My fish are killing each other. It's frustrating. I spend so much money on these aquariums. I will try these tips

[Katavi_]

Thanks man this really helped, I moved the decorations around they they almost immediately stopped nipping each other, now the new fish is happy.

[Prizzlesticks]

Thank you!! My pepperming platty was the sole survivor of Ich in my previous setup. ;-; A very cute fish. I think being alone so long made him depressed, because he was constantly at the bottom of the tank and not eating much or swimming... I got two beeeeautiful albino guppies and a snail after a time, and he immediately perked back up. It was great to see him swimming all over, being a very active fishie again.


A few weeks ago, I noticed the smaller of the two guppies had been hiding a lot more, and the larger one had a tear in his tail. He got a few more tears, and I caught the platty chasing the guppies around, sometimes pushing them into the tank glass, being a big ol' bully. My guppies are such gentle fishies, and the little one had stopped eating unless I secretly fed them at night while the platty slept.

I cycled a spare tank and separated the platty out. He's still swimming around and active, which I was afraid he'd get depressed again. But I wasn't sure how long to keep him apart for, or if I could ever move him back at all. You answered the question in your video, and I'm so grateful! None of the sites I was looking through had an answer to that.


I'll try returning him to the nice tank at the end of the week and see if his bullying stops, or maybe until the other guppy's tail heals all the way.

[Zenith]

The thing he said in the end is Actually very effective, it works if the aggressive fishes doesnt stop harassing, just turn off the lights and make it dark enough, but not too dark, this will calm them down a bit and help them Not fight or be aggressive to one another, but this doesnt work all the time, sometimes they will still be aggressive but less, or they will start being aggressive again once the lights are on, or if ur lucky enough they wont get aggressive and start ignoring or respecting others.
I learned this the hard way, if ur fish gets bullied please remove the aggressor or if theres multiple harassing one, its best to seperate the bullied away from all the fishes, put them in a tank, if u have a spare one, a bucket aint as good, make sure ur fish is healthy, if its weak, look up some things how to help the fish heal. I hope this helps :p
Fish keeping is very stressful and hard, im new to this but im learning my way to hopefully make my fish live a happy and healthy life.

[inkedglass]

I tried rearranging my tank the day I noticed the fish wasn’t looking well. His fins were torn and he was in the corner. Unfortunately I was too late, he was belly up within a few hours. :(

[TheBeautyNeuron]

it worked like magic! Thank you so much!! The aggressive fish was clueless 😂

[naheek]

One of my pleco has grown so much and has been bullying my 2 kio fish.
It's a large tank, but still it's very territorial. I tried many methods and finally decided to change the tank setup and it all worked fine.
The pleco stays on the more darker area with hiding spots while the kio stays near the toy soft corals.

[UnfilteredJustice]

Use an isolation box. Keep the new fish in it a few days inside your main tank. All fish will go up to it, may try to attack it, but will eventually leave it alone. After the other fish stop going up to the box for a few days, then set it free into your tank.

I've kept many incompatible fish using this method. Some fish may square off with it, realizing it's out of the box, but doesn't last long.

You can also toss the aggressor into the sump for a few days.

[NikkiSDuke]

Thank you! This worked pretty much immediately. Really appreciate the tip as do my fish that were getting chased!

[littlelaughable]

my Flying Fox has just started to chase one of my guppies around and it's so frustrating.. thank you for your help!

[cryindeath]

Please help!! I bought 2 glofish tetras about a week ago for my 5 gallon glofish tank. (Yes I'm aware I need to invest in a BIGGER tank). The bigger tetra has bullied the smaller one so badly that it sits in a corner for most of the time. Even when eating time it chases it away. I re-arranged the plants, even took a few out so it wouldn't be overcrowded and nothing worked. I went to my local pet store where I was suggested to get 3 zebra fish to break up the fights, it didn't work. He still chases the other tetra around but doesn't chase after the zebra fish. How do I help my bullied fish?

[Sxchiko]

My new fish all got along well for a week, after a water change a week later, all the fish was swimming happily till one start chasing the other a few days after.

[stonigee]

Just stopped by to say the thumbnail to this video is hilarious...

[chantiawhissell]

this helped alot thank you! I have a betta and introduced them too soon. I was worried I have him in a plastic cup floating with the new fish I noticed my tetras are starting to explore instead of staying in the one corner

[tobiasgriffin]

All in under 3 minutes😳
Awesome video!

[ianeckhoff]

Birds are some of the most aggressive things on Earth, too. Downright vicious.

[rileygentner]

as im watching this, im trying to stop my target fish from attacking my lol