How To Stop a Bully Fish

You’re finally finished. Your tanks cycled, the plants look beautiful and a new fish is on the way. You release them into the water and watch as they begin to mingle but something isn’t right. Your original fish are herding the new fish around, pushing them and keeping them away from prime locations. When you feed your fish the new tank mate doesn’t dare go near the rest as they eat all the food, leaving them hungry. You have a Fish bully and it needs to be dealt with.

Fish are not like most pets. We can’t just spray them with water when they do something wrong, and we can’t put them in a time out either. This presents us with a unique situation where we have little control over our pets behavior. Follow along as we reveal every tip there is on how to get your fish bully under control and stop aquarium bullying.

The Initial Fighting

If you are fortunate to see the first fight try to remember it in detail. How long was the fight? Were both fish fighting or was it an assault?

When two fish fight for the first time it will often be to establish the pecking order of a tank. Given one or two short conflicts most fish will stop fighting as they know who is stronger and see no reason to fight. For those lucky enough to see the first fight try watching your fish a second time before taking drastic action. Does the bully fish no longer chase the other fish more than a few inches? When feeding your fish, are they all able to get food without being hit by one another? More often than not they will have stopped fighting.

However if you have had your fish for several weeks and are just now noticing the bullying, then a pecking order has long since been established and the bully has other reasons for attacking.

So why are our old fish being so aggressive?  Established territories are a common fight starter. Large aquariums where the territory is a relatively small portion of the aquarium do not usually see issues from territory creation.

When fish age they get larger. While this can seem obvious it also has the subtle affect of making the aquarium smaller. While several young fish may have gotten along, they may see the other adults as taking their home. Try build a tank around the final size of the fish, even if it means having an empty looking aquarium with guppy sized fish for a few months. It’s a bad feeling when two of your favorite fish start fighting after years, especially when it could be prevented by better planning.

Some species like Betta fish and tiger barbs are naturally aggressive. To keep them under control you much purchase only equally aggressive fish. This stops bullying as neither fish will want to fight someone who will fight back under normal circumstances.

While many fish stores will have an aggression listing next to their fish you should do a bit of extra reading about them before adding them to the tank. Common bullies that get into our aquariums are cichlids and damsel fish. They are only rated as semi aggressive but can even bite humans who are cleaning the aquarium. While these two fish behave around similar aggression fish they will almost never stop bullying things that are weak.

Fish Size Does Not Matter

You may think only the large fish can pick on small, new fish who cannot fight back but this is not true. Easily noticeable in Tiger Barbs, small fish can harass fish of any size if they are too passive. Always check fish compatibility charts to ensure your fish won’t be at each others gills

In cases regarding peaceful fish suddenly turned aggressive or properly managed aggressive fish starting new fights, the issue often lies in how your tank is laid out.

Redecorating Your Fishes Home

For starters, turn off your aquariums light and work in fairly low light. This keeps the fish from focusing on what you are doing. With the lights off begin to re-arrange your tanks decorations and equipment. Make sure nothing is in a similar spot and turn the lights back on.

Why are we doing this? Over time animals create nests and territories which they will protect much more adamantly than others will. Fish are no different, and having bully fish claiming the higher levels of your tank can keep new fish from ever seeing a flake of food. Keep your fish guessing on where its territory is. While your old fish are looking for new areas, so will the new fish. Given the same start your two fish will both pick their own areas. Your old fish will be fooled into thinking they are in a new area, putting them on even grounds with the newcomer. This stops the majority of fish aggression, and is our favorite method.

Adding New Hiding Spots

Some fish are just too docile to be around other fish. These guys need a place to hide and not a territory to defend. Based on your fishes size there are a few ways you can go about doing this

  • Adding live plants will give your fish more areas to hide. Tall plants can create walls while a dense forest of stems can allow your fish a safe shelter. Be sure to tailor your plant selection to what is already in the tank. If you have a lot of walls get something that provides shelter. If you have a lot of low hiding spots give them some tall plants to swim behind
  • When building with rocks choose thin, long rocks. These allow you to make structures with plenty of hiding spaces without taking up much water space.
  • Find plastic decor with passable areas. Many owners own plastic plants, but these can cut fish with sharp edges, which deter fish from the hiding spots they create. Instead look for things like castles, columns or other items without sharp edges. Anything to give your fish some cover will do.
  • Move your equipment so that they create hiding spots. Bubbles in the back of the tank look nice, but a wall of bubbles a few inches in front of the back wall can give your fish the obstruction it needs to relax. On the other hand do not have equipment take up too much water space.

Bully fish only strike out at nearby fish. Remember this as you arrange your tank. You want hiding spots but don’t condense your tank into a smaller area in doing so. Under sized aquariums are one of the biggest reasons peaceful fish turn aggressive.

Over Stocked Tanks

When there are too many fish in the same tank there is just no solution. Try as you might there is a finite number of territories fish can create in a tank. Even when given an equal chance at scouting a home out some fish will have to lose the race. Nature is survival of the fittest after all. That’s why we try to bring down the difficult of nature to allow all our fish an easy, stress free life.

Keep in mind the types of fish you keep can affect what an over stocked tank is. Keeping loaches around other bottom dwelling fish will create tension as all the fish are at the bottom of the tank. Using a mix of high swimmers and low to bottom swimming fish will help reduce aggression in smaller aquariums.

Special Note on Breeding Fish

When housing multiple of the same species, we may often meet their optimal breeding scenario. Either through research or while simply adjusting the temperature, many owners will find themselves with breeding fish at some point in their aquariums life.

Fish that are of the same sex will fight during these times, defending their territories and driving away any competition. If your fish are both of equal size and aggression these fights will not end until only one fish remains. For this reason breeding parameters should be avoided when housing large groups of one species, and those who are meant to breed should be separated from the tank. This can be accomplished using breeding nets, tank dividers or another aquarium all together.

Please note that similar looking fish may consider the other to be in the same species. Watch your fish’s reaction as other tank mates swim past them and learn who he likes and dislikes. A short chase of two inches means they are safe, while a long unending chase is a problem that will not be solved without intervention.

Because of these difficulties in gender and species confusion we caution new owners to try schooling fish, being sure to follow the specific guidelines for each species. Generally you will want at least two females for each male.

Play Fighting

In some instances, like clown loaches, fish will play around with each other in a very aggressive manner. if their bodies are tougher this may not cause an issue. If these fish are not kept with others of their kind and they try to play with other, more delicate fish the rough housing can easily hurt them.

The Unstoppable

If all attempts to stop bullying have failed then your fish may just be too aggressive for it’s tank mates. While compatibility charts will typically avoid this problems, some fish will simply break the norm and be far above their normal aggressive level. In this situation it is best to:

  • Remove the bully from the tank
  • Return them to the store they were purchased from. Many stores will take back fish if you return them soon enough.
  • Donate the fish to another aquarist

Keeping a bully fish who cannot be made to behave is not advised. They will continually harass your other fish to the point of their death. Even without causing bodily harm, the stress bullying puts on fish is actually enough to kill them. Removing your fish is of course a last resort, but safety of the tank must be placed above all else.

Looking for more interesting topics? check out my new page on what eels eat

17 thoughts on “How To Stop a Bully Fish”

    • Fish will pick on:

      Similar looking fish
      Other Males
      Meek/less aggressive fish
      Smaller fish
      Fish that come into their territory

  1. No matter what new fish I add to my communal tank it is bullied to death within 24 hours. I’ve tried moving stuff around low lighting, no lighting.

    • This is something I would need more details on. Rarely is a fish bullied to death in a day. It sounds more like the fish are straight up attacking the new fish until it dies and not stressing them out.

      Be sure there is unused space in the tank where the new fish can hide. To do this check on your fish multiple times throughout the day and see if there is any large areas where fish are rarely hanging around.

        • What kind of fish is it that is missing their scales?

          I couldn’t imagine an algae eater, something like a cory catfish or pleco would attack anything that is alive.

          The zebra danio could be aggressive if the tank is smaller and he does not have a few other danio fish with him. Danios like to swim fast and in bursts, so they can be aggressive in shorter tanks. If that is the case try to put most of the decorations in the middle of the tank so that the danio has a straight path in front of and behind everything in the tank.

    • I got two tropical fish yesterday.

      One fish is just constantly chasing the other one around the tank.

      How long do I give them before I take him back?

      • This depends on the two fish. If they are commonly kept together, like multiple tetras or fish that you try to form a mated pair with, then I would say a week with monitoring. Check to make sure no damage is being done to either fish and observe how often the fish is chased as well as how long.

        The chasing could also occur due to one fish having a territory in the front of the tank. This gives aquarists the idea that the fish will bully others when they swim out at all when in fact they are defending their own space.

        For fish that are kept with caution, as in one is often a threat to the other, I would only give them two days with heavy monitoring. If the bullying is bad enough you may even need to take the bully fish out of the tank for a time out period. In this time the target can get established in the tank, making it more difficult for the returning bully fish to harass them.

  2. I got a new sail fin molly 3 weeks ago who is a maniac. no matter how much food he gets he is always bullying the other fish at feeding. he even stole the algae wafer from the corey cats and ate most of it. 38 gallon tank is not over stocked- besides the molly there is one dwarf gourami, 3 corey cats and 10 tetras.

    tried new territories, adding food at both ends of the tank to separate fish, feeding corey cats at night in the dark, and even tried extra feedings which spiked nitrates but not the aggressive feeding of the molly. i think he is psychotic from being raised in a fish farm 🙁

    any suggestions before i give him away?

    • Sail fin mollies need more veggies or algae in their food than tetras so they will usually eat a good amount of the wafers you put into the tank. Try to use more plant based foods rather than more food over all and see if this lets you feed everyone without the nitrate spike.

      It is odd that they would remain hostile for three weeks, especially with tetras which are a good pairing for them. If you wanted you could add 2 female sailfin mollies to the tank which should calm the male down. They would probably breed, making it more of a molly tank, which doesn’t seem to be your aim as you have a good amount of fish and have just added a single molly.

      The dwarf gourami should be getting after the sailfin when he acts up. Is the dwarf gourami still small?

  3. I introduced a Koi Angelfish into a tank with a single Blood Red Parrot Cichlid and the parrot spent the entire night chasing around the angelfish. Since I woke up, the angelfish has been at the top of the tank (still alive) and the parrot has been coming up periodically and nudging it and trying to nip at its fins. Whenever I look away it bullies it. To the point where i walked in earlier and the parrot was pushing the angelfish into the substrate upside down. Is there a chance the parrot will get over this or is my angelfish a goner?

  4. I have 4 Tetras in my tanks and I think one is becoming a bully to the others. 3 hide at the back while one takes over the rest of the tank. I see what I would describe to be chases going on. As they are all the same it’s hard to follow which fish is which but I’m attempting to do so. Is this kind of bullying still likely when they’ve been together a few months and all joined the tank at the same time? As well as all being one species. I intend to add new different types of tetras to my tank but am conceded as to whether this bullying may help or hinder. Thank you

    • bringing in a second school of tetras is risky and should be done only with larger tanks. It sounds like the 4 existing tetra may have a dominant male. These will do short chases after the female but it should not involve any attacks or nipping. Bullying will either subside as they get used to each other over the months or intensify as they age. As tetras do not have a particularly long life I feel they would more than likely calm down as they should be young when recently added.

  5. Today I just got a Dalmatian Molly to go with my guppy and the guppy has been following the molly around everywhere. Is this aggressive behavior or is it just checking the new fish out?

    • Fish will almost always check out or even harass a new fish for a short while. The behavior should not last more than a few days and should be short interactions. Constant bullying for their first day shouldn’t be allowed but quick chases every couple minutes is not a cause for concern.

  6. I have 3 dwarf gouramis had them for about 4 weeks came with the tank one is very aggressive towards the other two tried most things but still chases after both constantly shall I just get rid of him

    • If a long established fish cannot be calmed down by rearranging the tank with fish its own size then they should be separated. It’s interesting that fish who came with the tank would be fighting seriously enough to cause concern. I would try a spacious lay out with several well separated territories for the gouramis


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