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How to Manage an Aggressive Fish

Updated on December 19, 2021

Aggression can begin at any time...

Once you have established your aquarium and have a nice, congenial mix of fish, you may one day find yourself alarmed and dismayed when one fish suddenly takes a notion to start terrorizing one or more of it’s tank-mates. This can happen for a number of reasons.

Sometimes Aggressive Fish are Happier Alone

 Title: Lionfish in the Red Sea ~ Attribution License: ~Photographer: Zpyder:
Title: Lionfish in the Red Sea ~ Attribution License: ~Photographer: Zpyder:

Melafix is a good tonic!

  1. One fish may become ill causing others to begin picking on it.
  2. Some fish become aggressive when they reach a certain point of maturity. This is one of the many reasons to do your research before you choose your fish.
  3. An increase in temperature or change of seasons may cause some fish to become aggressive.
  4. Some fish become aggressive when they are ill.

Regardless of the reason, you will want to remove the aggressor. Even if the fish being picked on is being picked on due to illness, you will want to separate the aggressor. Once they start aggressing, they usually continue. If you remove the object of aggression, the aggressive fish will be highly likely to pick on someone else. The exception to this would be if many fish are picking on one fish. That would be a clear indication that the one being picked on is ill and should be removed.

If you do determine that the aggression is occurring either because the aggressor is ill or because the fish that is being picked on is ill, you will want to treat for illness in both the main tank and the tank you move the aggressor or ill fish to. The first treatment should be Melafix, a natural, overall tonic that has calming properties. Keep this on hand so that you can use it as needed to handle illness and stress. If the problem isn’t cured with Melafix, note the symptoms of any illness your fish are exhibiting and take a trip to your local fish store to locate the proper medication. Whatever, the illness, Melafix may cure it, and if it doesn’t, it will calm and soothe without doing any harm.

Now, back to your aggressive fish. Where will you put it? It is always a good idea to have a small tank ready to receive injured, ill or aggressive fish. One good way to keep a tank set up and ready is to keep a three, five, or ten gallon tank set up with a single Siamese fighting fish. In this way, you will always have a seasoned tank ready to act as a spare if needed. When you need to use this tank temporarily to house a sick or aggressive fish, you can always move the beta out to a fishbowl temporarily.

Once you have separated your aggressive fish, you will need to decide what to do with it in the long term. I am very fortunate to have a local fish store that will trade fish, so I have taken quite a few fish that got too big or aggressive back to my local fish store and traded for something more appropriate. Another option, of course is to advertise in your local paper or on Craig’s List to sell or trade your aggressive fish.

If you are very fond of the fish, you may decide to set it up in it’s own tank. I have done this a number of times with favorite aggressors! The advantage of keeping this kind of fish in it’s own tank is that aggressive fish are usually full of personality. Kept on their own or with one or two fish that agree with them, they can be very special pets.

Copyright: SuzanneBennett: June 6, 2009


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