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Dealing with Bullying Between Fish

By: Hsin-Yi Cohen BSc, MA, MSt - Updated: 22 Jul 2023 | comments*Discuss
Fish Bullying Fish Bully Aggressive Fish

You’ve finally got your tank set up, the temperature right, the plants thriving and the water filled with a variety of fishy inhabitants – and you’re all ready to sit back and enjoy your aquatic micro-world. But what’s this? One of the fish seems to be constantly harassing the others – picking on the smaller fish, not allowing them access to food, swimming aggressively into them with a head butting motion. The other fish are starting to show signs of stress, hiding in the corners of the tank, some even sporadically floating on their sides – but certainly, not fighting back. Welcome to the world of fish bullying! So how do you deal with it?

Why Does it Happen?

Fish can become aggressive for a number of reasons. One of the most common is territorial behaviour, especially during breeding time. Some species can become very possessive of certain areas in the tank, particularly if they are guarding a nest or spawned young. In such cases, it can be best to just give the fish enough space to carry on “as nature intended”. In general, if you have fish that are near or actually spawning – or even looking after young, it is a good idea not to trust them with other fish, especially if the other fish are not of an appreciable size.

Sometimes, fish can just be territorial in general and will set up an invisible area that they regard as their own and prevent other fish from entering it. Adequate space is a very important consideration in a tank – for example, most goldfish need around 10 gallons of water each to remain in good health. If they feel overcrowded, they will become more territorial and will start to display their stress through harassing, fighting and generally bullying the weaker fish. Food is another consideration as fish will fight over food if they feel that there is insufficient amounts to go around.

Unfortunately, sometimes – like in the human world – some fish simply don’t like each other. In such cases, sadly the only solution may be permanent separation.

Size Doesn’t Matter

It is a popular misconception that only bigger fish will bully others. Certainly many of the bigger species, such as the Cichlids, can become very dominant as they mature and will reach a stage where they will only tolerate fish of a similar size or bigger than themselves. But it is not uncommon to find a smaller “cute” fish bullying others much bigger in size. This happens more frequently during breeding time but it can also just be down to the individual personality of the fish in question. Unfortunately, even with the most careful selection, you may not be able to get all your fish to live in harmony. For example, the colourful Dwarf Gourami is usually quite docile but this can all change during breeding time – in fact, this little fish can become the terror of the tank, especially if nest guarding, attacking and bullying other fish twice his size. Most of the Gourami species and the Bettas will display this behaviour in such circumstances.

Make Sure They're Not Love Bites!

Before you panic about fish bullying, make sure that you’re not simply observing mating behaviour. It can be easy to confuse this with bullying as many species will look and act aggressive during breeding time. Cichlids, for example, will lock jaws and chase each other around –and it can look like they are going to tear each other apart! Similarly, with Live-bearers, the males will constantly harass the females, even to the point of exhaustion and the only solution is to remove the females to another tank if they seem to be experiencing too much stress.

So How to Deal with Bullying?

You can try a variety of things to stop bullying. Check the amount of space in your tank and increase it if possible, so that there is less likelihood of overcrowding and stress. If you have a particularly dominant fish who is guarding areas of the tank, try rearranging the tank completely so that it becomes confused about the boundaries of its territory.

Often, fish that bully tend to be the only representative of the species in the tank, such as a lone Angel or Oscar. In this case, a frequently successful solution is to introduce another fish of the same species to distract the bully.

For the more docile occupants in the tank, you can add more places for them to hide, such as through additional planting or rock arrangements - it is especially good if you can provide some hiding places that the bullying fish can’t get into.

As a last resort, you may have to think about keeping the anti-social fish in his own tank or even rehoming it to a fellow enthusiast or even back to the pet store or fish suppliers. Some may be willing to trade a large fish for several smaller ones.

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I have 3 Bolivian butterfly rams not sure the genders,but at the start all 3 were fine but just recently we’ve notice 2 have paired upbut mainly 1 has been bullying the 3rd into corners or not allowing it to come to the front of the tank. I tried changing the tank layout a bit and have been monitoring any colour changes to ensure it’s not too stressed but with the layout changes the pair are still being aggressive.any advice on if we should get another one to balance the number of them or does it sound like we should return the one. Thanks!
NIC - 22-Jul-23 @ 9:22 AM
I have a blue gourami that has been living with 4 platty’s and a yoyo loach. I noticed a couple of my fish missing. I decided to get three more fish - to mollies and a platy. After the other fish disappeared, I made sure to pay close attention to the tank and noticed the loach eating at the bottom of the tank. Well, he was chowing down on one of my new molly’s (and now I know where my missing fish went). He continued to chase the remaining of the new fish so I decided to bring him back to the store. I gave my tank time to settle then proceeded to get 3 new fish. Well, now my blue gourami attacks ANYTHING new put in the tank and even turned on the other fish that started in the tank with him. I netted him in his own space for a week and when I did release him he was good for a day and a half only to kill the other fishes. I now only have one platy in with him and won’t be surprised if he kills that one. Is it hopeless to put any fish with this guy?? Why would he all of a sudden become this way?? Should I re home him and start all over? Thank you for your time~ Brenda
Bre - 26-Apr-21 @ 2:43 AM
Recently put 12 new Africans in my 55 gallon tank. Many rocks and hiding places. After 2,3 days one of them, obliquidens, began bullying to the extent that none if the other fish are allowed in his half of the tank. All fish are males. I’ve recently added two huge objects in an attempt to confuse. Hasn’t worked. I’m thinking of removing him. Any suggestions?
Ted - 21-Mar-21 @ 5:46 PM
Hi. Would like some advice,I am having to take out a male swordtail,as it is bulliying the other two swordtails,who are male. I have a spare tank,with a new filter and heater can I transfer water from the main tank and place the bully innit?
Bob - 10-Sep-20 @ 4:09 PM
Hi, I'm hoping someone can help. My elliotti cichlids bred not long ago and I left them to raise the babies by themselves.They babies are now one inch long and are doing well but now my male is constantly attacking the female. I've taken him out for a few days at a time but after a few days he starts harassing her again. I don't really have the tank space to be moving fish around and was just wondering if he's doing it cause he wants to mate again ? Thanks Lee
Lee - 16-Aug-20 @ 3:54 AM
Hello, I am taking care of my Dad's fish since he passed away back in January.I know how to clean the tank and such but I am not familiar with tropical fish behavior.There were four angelfish and one just passed on Saturday.Anyway, since there are three left now, two of the angelfish seem to be ganging up on the third angelfish and keep backing it into a corner in the tank.I'm not sure what to do.One of the angelfish that has been part of the bullying has been laying eggs recently but has since eaten all of the eggs, so I'm not sure if that could be the issue.Any advice would be appreciated! Thank you!
Ruthie - 3-Aug-20 @ 4:22 PM
So, I have this big blue gourami. A couple years ago he suddenly go aggressive in chasing and forcing all the other fish into small zones. Not nipping, just chasing. I had to move him to a 6 gallon tank with some red plattys, never bothered them. Had no probs with chasing in that tank I needed to clean that small tank, so, thought I would give him a shot in the 20 gallon. Was OK for a few days, some fun chasing of the 2 golden gouramis. But, then, chasing the golden barbs, red tetras, coreys, and even the platys that were in the small tank with him. Now they are all in like 1/4 of the tank. Still not nipping, just bullying. I don't want all those fish limited to such a small area. I've rearranged everything once, will try a few more times just to confuse him, see how it goes. I really don't want a second tank. Any other ideas? They are well fed. I have a big live plant and some hiding spots.
Wteach - 7-Jul-20 @ 6:41 PM
I’ve got 25ltr tank with 4 betta had them for months now , they were all doing fine ... omg one started to grow so big and think he is a male and I have 3 females nightmare but I’ve kept an aye out and only one seems to be getting bullied but off the other females the biggest one just hides half the time I’m lost found the little one stuck behind the fliter look like he been torn to bits what do I do I’ve taking it out of the tank I could cry ... don’t have another tank
Jen - 11-Jun-20 @ 11:07 PM
I have rwo angel fish and I've just introduced another angel of similar size and its getting bullied should I buy another one to make it up to 4 will this stop the bullying
Lynsy - 7-Jun-20 @ 9:03 AM
I have quite a large tank with only about a dozen community fish. Just recently the only penguin fish is intimidating the only hatchet, which hides above the filter at the top of the tank, in the corner. I did have 3 hatchets but 2 died. I know they prefer to have company. Any ideas?
Evie - 19-Oct-19 @ 2:41 PM
@1KoolCid1 - sounds like it is being attacked. I'd separate them.
RiN - 7-Aug-18 @ 10:54 AM
My red scat keeps continuing to bite and nip at my Archerfish. I have recentaly gotten a baby green scat that stays near the older red one. Over the past few weeks I have noticedthat myArcherfish has chunks of scales missing, fins shredded, and what looks like blood coming from missing scales. If anyone knows what to do please tell me. Thank You in advance
1KoolCid1 - 4-Aug-18 @ 9:38 PM
If they are the same fish and one of the fins look eatin on what do i do? Im getting nervous because i nevee see them fight or anything!
Fishlife - 20-May-18 @ 3:15 AM
I've set up a tank everything is correct now I've adde the fish the water has gone murky why? And how do i fix it? Fresh water topical. TAI
Jo - 26-Feb-18 @ 4:47 AM
@Shaunaa - separate them again. The dominant fish is obviously bullying the other fish as it's probably not up to being able to stick up for itself. Survival of the fittest- they'll always try and kill the weak. The other fish has now marked that tank as its territory.
RoB - 8-Feb-18 @ 12:53 PM
I have two fish a very long time but one got sick so I had to separate them for a while now I have put him back into the tank my other fish seems to be pushing him around, pushing him against the glass of the tank and not letting him at the food what should I do ?
Shaunaa - 7-Feb-18 @ 3:40 AM
I have 2 large parrot fish one seems to Be bullying the other is this common
Gwenba - 11-Jan-18 @ 12:32 PM
My guppy fish is quite old and before I was observing them and I saw a my phantom fish bite it on his tail vigorously. Then I realised my fish was very scared and anxious, he was hiding behind the filter from the other fishes. Later when the other fish had gone he went back and lay on the ground, until a group of fishes came and he got up and was kind of being territorial. I gues thats nature. But how can I prevent it?
Andrea - 27-Dec-17 @ 2:31 PM
@April - I think the article says it all. I had to separate mine :(
GaxC - 18-Dec-17 @ 12:36 PM
I have a 22L tank with two Varius Platy fish. They have a lot of space but one of my fish seems to swim aggressively into the other one whenever he goes in a certain area.I assume this is him being territorial. If I rearrange the decorations in the tank, would that help in any way? We're unable to get another tank to keep them sepereate but I'm desperate as I care a lot about my fish and I'm not sure what to do.
April - 16-Dec-17 @ 11:06 PM
Olivia - Your Question:
My mom got my brother and I a fish tank 2 weeks ago and so far all of our smaller fish have died except 1 but he is not eating and is hiding behind our filter

Our Response:
I am sorry to hear this. The link here may help you further.
TropicalFishExpert - 9-Oct-17 @ 12:01 PM
My mom got my brother and I a fish tank 2 weeks ago and so far all of our smaller fish have died except 1 but he is not eating and is hiding behind our filter
Olivia - 8-Oct-17 @ 1:56 PM
I have 3 platys in a 19ltr tank ( I've been told this is too small) however I did have 4 one died last week as was picked on by the biggest platt in the tank. Unfortunately now it's attacking another. There all males, and I dnt have a heater I was told to keep track of the temp for now to see if I need one invade this cause the aggression. I dnt know whether to take him back a change him or leave him, he is really friendly with the other fish though apart from the 3rd he wants to kill
Sarah - 18-Jun-15 @ 3:14 PM
We have two elephantnose fish, about six and eight inches long.The bigger oneis a bully, chasing the other one all over the tank and out of all the hiding places, of which there are many.We got the advice to introduce another elephantnose and could only find a smaller one, which is now also being bullied.(Not very brainy, I know!)At this stage, we have removed the bully to our smaller guppy tank, but it will not be able to remain there for long.Is the only solution to take it back to the pet shop?We would really like to keep it, as we have been feeding it bloodworm three times a day, calling it Dave the Dolphin, and observing its surprisingly intelligent behaviour.
Renette - 20-Dec-13 @ 11:10 AM
I have two angle fish that I have put in three day ago but one is chancing the other one and won't stop what do I do
Angle fish - 6-Sep-12 @ 11:46 PM
The problem is that once a fish is stressed it will take a while to regain its confidence, just like a human who has been bullied. Once you've dealt with the bullying itself you'll need to help the stressed fish regain its confidence. Providing it with hiding places can help (even if it is alone in its tank), as can slowing down your movements as you approach the tank so that feeding and cleaning times never come as a scary surprise. Tetra and Interpet both make a General Tonic that can help by giving your water quality a boost and getting rid of the smell of stress that can trap an unhappy fish in a vicious circle.
Jennie Kermode - 7-Aug-12 @ 5:46 PM
Same, my other fish that's getting bullied is constantly going into the corner, going up and down. I've tried separating them and the fish is still scared of something
egeag - 24-Jun-12 @ 8:48 PM
My cichlid keeps going by the corners of the tank and swimming up and down...is he stressed
Sac attack - 4-Mar-12 @ 3:11 AM
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