Aggressive then sulking male goldfish

ElectricLee

Hi everyone,

I know male goldfish aggression has been covered extensively before, however I could do with a little advice please.

I have a 450l tank, with two fairly big external canister filters, tanks been running for about 8 years in current location.

I have 4 standard goldfish in the tank, 2 are about 3-4” long, one is 5” and the other about 6”. The largest one is absolutely battering the others. Theres 2 males, and the other two I haven’t confirmed, but I suspect are females. He chased one of the others to the point where it jumped out of the tank and had to be rescued.

I fitted a tank divider about a fortnight ago and now he’s either moping or flinging himself at the divider trying to get at the others. He’s ignoring his food. I’m worried about him and wondered if anyone had any ideas? I tried reintroducing the other male fish but he decided he was going to beat him up too.

He‘s unusually coloured and seems very butch for a goldfish tbh. He was jet black until about 3 months ago (got him in 2019) now he’s showing the kind of colour change I’d expect for a young fish, with the dark colour fading out from bottom to top. I’ve added a photo of him from September ‘21 vs now.

Thank you in advance!
 

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jtjgg

hi and welcome.

most likely mating season. the females release hormones and the males chase them. blocking him off is just driving him crazy. he needs to be moved to a different tank with fresh water, don't use any water from the current tank as it will contain the mating hormones.

black is the most unstable color in goldfish, even some Black Moors will lose some or all of their black color after a few years.
 

ElectricLee

Thank you,
I have a spare 100l, I’ll move him over today.
The other male is behaving normally so I’ll leave him where he is.

Thanks again
 

ElectricLee

Very quick update. Turns out 3 out of 4 were male and the second largest was female. In the end I’ve isolated her in another tank, done a couple of fairly large water changes in the big tank and peace has returned.
I think I’ll rehome her rather than put her back in with the males so we don’t end up with a repeat next year.
Thanks again!
 

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