I've got alot of them in ours. We have caught over 200 hundred in the last year and a half and still feel like we haven't dented them yet.
The problems they cause for me is that they eat forage intended for other species. They are prolific predators. We have caught 1 pound bullheads by using 4 inch bluegill! They also sometimes eat pellets.

Once they get established they are very difficult to get rid of.