Recently my 55 gallon tank has had a problem. The problem is my big 5 inch common shiner, currently the biggest fish in my tank, he had a recent growth spurt and even out grew my creek chub who also had a recent growth spurt. He went into breeding mode, staked out a terretory, and has gotten really agressive chasing any fish out of his terretory he sees. Today he went a step further and ventured to the opposite side of the tank to chase fish. I worry he may soon break the "inch and a half safety limit" and turn his agression into predatory behavior on my smaller minnows.

I am not sure what to do, i think he's a bit big for my 10 gallon agression tank (which houses a dollar sunfish and a bullhead).

Anyone have suggestions on calming a common?

More shiners to diffuse the agression, and of course more filters to accommodate more waste. IME Luxilus shiners rarely eat small fish, if well fed. (NOT so for creek chub!) Does he chase the little guys too, or mainly the ones that are closer to his size? Your other option is MORE TANKS. Just be glad he's not a Cyprinella - talk about mean!

Recently my 55 gallon tank has had a problem. The problem is my big 5 inch common shiner, currently the biggest fish in my tank, he had a recent growth spurt and even out grew my creek chub who also had a recent growth spurt. He went into breeding mode, staked out a terretory, and has gotten really agressive chasing any fish out of his terretory he sees. Today he went a step further and ventured to the opposite side of the tank to chase fish. I worry he may soon break the "inch and a half safety limit" and turn his agression into predatory behavior on my smaller minnows.

I am not sure what to do, i think he's a bit big for my 10 gallon agression tank (which houses a dollar sunfish and a bullhead).

Anyone have suggestions on calming a common?

More shiners to diffuse the agression, and of course more filters to accommodate more waste. IME Luxilus shiners rarely eat small fish, if well fed. (NOT so for creek chub!) Does he chase the little guys too, or mainly the ones that are closer to his size? Your other option is MORE TANKS. Just be glad he's not a Cyprinella - talk about mean!

I wish I had room for more tanks. As for more shiners to diffuse the agression, I have about 13 or 14 of them and he's still agressive and after chasing them away sometimes the others grow agressive in return.

He chases both big and little guys. In fact the things he doesn't chase are interesting. He doesn't chase rock bass, chinese algea eaters, golden shiners, and fathead minnows. Everything else is fair game. He chases the little mountain redbellies, the big creek chub (who now covers in the fake stump due to him) and everything in between.

What's strange is unlike my agressive dollar sunfish who sent everyone hiding on the other side of the tank before I moved them, my other shiners seem to actively try and invade his terretory when he gets like this.

Have you tried re-arranging the decorations? That sometimes helps.