I have Specklebelly Sunfish (BGxRES cross) in my pond (with YP and tilapia) and they have been great so far. Eating well, getting big, and no nips so far. My kids were swimming nearly on a weekly basis in the summer.

Mosquitofish on the other hand! I originally put a dozen in when the pond when it was being dug so it wouldn't be a stagnant mosquito cesspool, thinking they wouldn't survive the winter in Southern Ohio. I have thousands of those buggers now, and they like to think my leg hair looks like mosquito larva. It doesn't hurt at all, but its annoying little pulls on them, haha.

[Linked Image from lh6.ggpht.com]