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How do I discipline my cichlid for attacking tankmates?


Registered Member
I have 4 cichlids in a 90 gallon tank with plenty of space and caves/hide holes. 3 of them get along and one is a total jerk. He is picking on one that is injured (I bought him that way) and I noticed a piece of fin missing on my albino oscar. I am not sure what else to do. I keep catching g him and putting him in "time out" but as soon as he goes back he does the same. Darn. Thing. I cant let him hurt my other fish so now it's to the point that I have to leave him in the net if I'm not watching them. I've been reading so much since I started the aquarium and other than this problem, everything is been great. I'm currently treating my tank with microbe-lift for the injured fish and I do not really want to set up a separate tank for this little turd because I'm hoping someone can give me some advice that will rectify my problem. The 2 healthy fish are Oscar's and are best friends. They defended the sick one against the mean one before I started giving him time outs. I need to figure out a way to knock him down a few notches so the other fish can get him to submit. I wish they made fishy harnesses so I could put him on a leash and restrict his tank access without having to put in a divider and take space away from the other 3. I thought Oscar's were more aggressive but the convict is giving my Oscar's hell. I have 2 Oscar's, one albino, named Bonnie and Clyde and 2 convicts, named Scarface and I cant even say what the mean ones name is lol.
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Global Moderator
Staff member
You can always try a stern talking to.

Like loach suggests, you can try mixing up decor in the tank to break up lines of sight, or re-home the fish.


While smarter fish, like cichlids, *can* learn things, it's apparently impossible to teach something as amorphous as civility to a fish. They can learn to go to certain parts of tank if given specific signals (I have a betta that'll go to a specific corner if he sees me with a food container in hand, for example), some will even learn things like *this* time is when I'll get fed and will actually know the time in "this is the part of the day when I get food" way. That's probably close to the extent of it. They just lack the cognitive part of the brain that allows that kind of comprehension. You're going to have to rehome him.


Fair, but I was trying to keep it simple.

That said, in this context, they're reasonably (definitely not exactly) interchangeable.


"With your powers combined . . ."
As said above, fish can time place learn and they can be conditioned, and I've just completed a collaboration on a maze learning experiment where minnows learned to navigate a simple maze, but they cannot learn stuff like this.

Convicts are known for their nastiness and cichlids will typically pick on weak fish. I agree with the above, try rearranging the tank or rehoming the fish.

Also, I want to bring up that netting and moving the fish to a "time out" is really stressful. Contact with the net damages the slime coat, making the fish weak to infection. Netting the fish and/or confining them significantly raises cortisol and makes the fish weak to infection. Also, if you expose him to air at all when you are moving him to confinement that raises cortisol sky high. The more often you do that, the more likely your fish will get an infection.