Aggressive goldfish help

[cloudy_starlight]

Let start off from the beginning: I had a black moor with my common goldfish in a 30 gallon tank, got them at the same time, have had them for about 5 months now. Well, a couple of weeks ago, Jack (common gf) started to chase, push my moor (Bugsie) up toward top and bottom of tank, so I moved Bugs in to his own 30 gallon tank. Well today we decided Jack seemed lonely and we got another common gf pretty close to Jack's size. And to my surprise Jack is being a butt and doing to the exact same thing to the new guy (Moe). I am feeling really bad about all of this and not sure what in the world to do now or what could be Jack's problem. I think he is crazy!! From what I have been reading these types of fish should not be aggressive and I am starting to think Jack is a female. What I have read females look fatter?
Any suggestions?
Thank you!!

BTW, just to let all of you know we are not newbies to fish, we also have a 55 gallon with 2 pleco's, 2 cory's and 5 dwarf jellybean chiclids. We just have no idea what could be wrong with Jack.

[Xavier]

I don't have that much experience with that kind of behaviour, but it could be mating behaviour, chasing the female and bumping underneath the other fish.

When I had common goldfish, they were rarely aggressive. Around feeding time the slightly larger one would try to chase away the smaller goldfish. They had been introduced at the same time.

I would assume that Jack has become territorial as well as bored. I would re-organize the tank, maybe put him in isolation somewhere for a few days and let the new one make a home for himself, then re-introduce Jack.

On a side note, like people, some goldfish are just big meanies. LOL!

[VoidParadigm]

Females being fatter is a common misconception. The best way to sex is around age 2-4, when the males develop breeding stars/pimples/dots/etc and the females simply don't. My best female is actually the skinniest of my commons. The softness of the rear, not the size, is usually a better way to tell if a female is a good breeder.

It's probably mating behaviour. Males will start exhibiting it earlier than they should breed. Bumping, chasing, etc all mating behavior. It's also not uncommon to see two male goldfish "schuffling" over bits of food or spots in the tank. Basically just looks like they're bumping each other out of the way. There's nothing you can really do, and so long as no one's getting their fins shredded (a rip or tear once in a while is fine), there's no need to stop it anyways.

Edit: As Hobbs pointed out, yeah, you could just move him to a pond or larger tank. That'd solve it. Commons really should be in 50+ gallons.

[Lady Hobbs]

Common goldfish reach about a foot long and he's too small for a 30 gallon. I'd give him to someone who has a pond. Make him happier and solve your problem at the same time.

[Meenu]

Welcome to AC. :)

I agree with rehoming him into a pond. Also remember that every fish has its own personality - just because the behavior is not common doesn't mean that it doesn't happen. You just got the psycho-serial-killer goldfish. ;)

[VoidParadigm]

If it's not common, then ALL my male breedable goldfish I've ever had are psycho-serial-killers. Hm. Just saying. :shrug:

[Meenu]

Heh... like a prison ward on death row. Housed with psychos. :D

My point wasn't that this behavior is uncommon, just that "normal" behavior isn't always what you'll see from every fish.

[VoidParadigm]

Fair ducks, and true point.

[cloudy_starlight]

Thank you all! I would love to put them in the 55 gallon, but that probably wouldnt be a pretty sight. Cause of the fish I have in my 55 gallon. I do not know anyone with a pond here, since we are military and live overseas. I did not know that common's could get that big, wish I did now. Here is a picture of Jack.
http://img812.imageshack.us/img812/5458/dscn5468.jpg

[Xavier]

That is one beautiful goldfish.

How big is he now? 2-3 inches? If it is a temporary arrangement, like several months, your 30 gallons is more than enough for Moe and Jack. I wouldn't put the black moor in with the commons though, since its vision is poor, making it hard to compete for food.

In that amount of time you can find a new home for them, get a larger tank and/or pond, or return them to the petstore.

[cloudy_starlight]

Thank you, I would say he is about 3 inches maybe 4. SO far this morning Jack hasnt been chasing or being a bully to Moe,but that could all change of course. Our black moor was in there with Jack until he started to be a bully to Bugs, thats why we moved him to his own tank then got another moor.