Never ever stick a flathead catfish in a pond. Channel cats are ok but my dad did this number of years back. Put a 12lb. flathead in our pond and ended up with only two grass carp left. The flathead died and looked like it swallowed a volleyball. Meanwhile the 40 bluegill, 40 crappie, and 40 bass up to 2 lbs. were all gone. Had a blue heron hanging around but I imagine he only got a few fish. Think about what you would use to go for flatheads. You would use fish. Fish eat fish.