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Dealing with Bullying Between Fish

By: Hsin-Yi Cohen BSc, MA, MSt - Updated: 16 Dec 2017 | 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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[Add a Comment]
@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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