In all honesty it looks like a Sunfish species.

gill is extended high and dark spot, Rounded and angled fins, you gotta sunfish for sure man.

hmm I'm not very familiar with those, but I got this when I was buying feeder goldfish, and the store accidently tossed this in with them, and I saw it and obviously it isn't a feeder goldfish...

It's a Native Fish In the north american continent, I use em' for catfish bait.

I agree, sunfish family, a lot of gold fish are breed and raised in big ponds(florida), we used to get these with goldfish shipment as well

It's a Green Sunfish. They always are mixed with goldfish for some reason. Look at my pics. You can see bigger versions.