Since fish really don't typically have mouths to tear fish apart, they have to eat the fish whole (at least the ones that are usually found here in North America). Once catfish (I'm talking about channel cats here) reach about 3#, they compete directly with LMB for food, switching their diet over to mostly live fish.
So, it all depends on your goals on whether to keep them in the pond or not!
If your goal is to raise as large of a LMB in the pond as possible, then they are taking up space, and eating food that the LMB could utilize better to meet your goal.
