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 cant 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 Fight

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? Some species like Beta 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.

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 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
  • 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.

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.

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.

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.

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

6 thoughts on “How To Stop a Bully Fish

  1. Mary

    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.

    1. Joshua@themandaringarden Post author

      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.

      1. Saige

        Yeah I agree my fish is missing an entire spot of scales on its side. He’s partnered with an algae eater and a zebra fish. Any suggestions on what to do?

        1. Joshua@themandaringarden Post author

          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.

  2. Tina

    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?

    1. Joshua@themandaringarden Post author

      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?


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