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Aggressive Goldfish


Carole

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I have had the same two small goldfish, Bubbles and Sylvester, in the same tank since last August and recently Sylvester has become very hyper and aggressive towards Bubbles. I found Bubbles with an injury on his side where it looks like he was bit because he had fish insides hanging out of his body.

I bought a tank divider for them and since then Bubbles has healed up nicely, but what do I do about Sylvester? Sylvester was always smaller than Bubbles and was always an easy going fish, but recently he had a growth spurt, grew larger than Bubbles, and started being aggressive. What do I do? I don't want to have to keep them seperated forever. Sylvester currently spends all of his time swimming quickly around in circles, pacing the clear divider like and angry dog running around on the inside of a fence. Bubbles also had an injury to his arm fin recently and now I suspect it was caused by Sylvester.

Would he become aggressive if I wasn't feeding him enough? Bubbles always comes up with injuries after periods where I am busy and might only feed them once every two days. Or is this just his personality as a larger fish? It is just the two of them in a 20 gal tank. Sylvester is about 3 in long and Bubbles is about that long because of his tail, but his body is a third the size of Sylvester. They shouldn't be to crowded.

Does anyone have any ideas?

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Hi Carole, sorry to hear you are having problems.

I do have a couple questions first.

What types of gf are they?

What is the water quality? (often if it is bad they can get strange on you).

There are many possibilities that could be going on.

It could be that you aren't feeding them enough. Feeding them every couple days on a regular basis could be a problem with them.

I would make it a point to feed them every day see if the problem persists.

Territorial aggression can happen in gf. So this is another.

On top of the questions I posed to you.

I think if you spend a great length of time watching them you could figure it out. Either way though it is not good to have them together if this continues. You may be faced with seperating them permanetly.

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Both GF are fantails. Sylvester is a classic orange fantail while Bubbles is a calico with a longer draping fantail.

The water quality recently changed. The tank has been cycled for a while now and I have had consistantly zero ammonia, nitites, and nitrates (I know that is a little weird though). Recently I got really busy and didn't change the water for like a month and the nitrates went from 0ppm to about 40ppm, which I think is still ok but it was quite a change. The pH is a stable 7.8. I have a good population of green algae going.

I have started making sure I feed them a couple times a day as they are generally happier that way.

Would it make sence that two fish that got along great for so long would suddenly have territory issues? Sylvester recently did get bigger but not so much that he is out growing his tank mate. Maybe I am wrong.

I really didn't want to have to separate them forever.

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Territorial issues could develope as Sylvester matures I guess. How big is their tank? Could it be breeding behaviour?

I'm a bit inclined to think that it is food related, especially if Sylvester has had a growth spurt recently. If I miss a feed in the pond I sometimes notice some of the fish have a few split fins. This indicates to me that some fish do become aggressive when hungry and try to take a bite out of anything that moves.

If this is the case then it's a bit of a problem because Sylvester has already identified Bubbles as a food source and the behaviour is likely to reoccur whenever Sylvester gets hungry.

Try to break the habit by keeping Sylvester well fed, even try feeding him twice a day until you see his behaviour settle down.

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Thanks for the input. It is interesting to see that someone else has had the same type of experience. The tank is a 20 gal and I don't think the GF are old enough or big enough to be breeding. They were just baby fantails 9 months ago. Also, Sylvester was never really chasing Bubbles around the tank, at least not from what I saw.

I will try feeding Sylvester more while they are separated until he stops thinking Bubbles is food. My other idea was to feed Sylvester less and Bubbles more until Bubbles grew larger than Sylvester. That would show him! :rofl

Does anyone else have theories about what could be causing this behavior?

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