Do they have silver sides (some having black blotches as well)? If so, they are Channel Catfish. Are they Brown or Olive colored? If so, they are probably Bullhead.
The Classic Michigander
The pond I regularly fish in near my house has alot of good sized bullhead. I've caught several in that pond that would have qualified for a Master Angler award (14" minimum) if I would have gotten them photographed.