Any uneaten food will increase your ammonia level and meat is knows to be even faster than other food. if you feed them liver, put small chunk (s) and retrieve after a while.
When training fish to new food this can be aproblem since you have to let it more time inside the tank. If you have to, it's recommended to increase your water change routine until the fish has learned to eat the new food.
It would really depend on the type of catfish as well. A flathead won't eat dead stuff, whereas most other cats prefer it. If it is one of those, you might try getting some stink bait, but I have no idea what effect it will have on the water.
I want a few some pumpkinseeds, has anyone tried them. They have really pretty color. I'm prolly gonna have pumpkinseed, bluegill, shellcracker, and a few smaller green sunfish, if my water cycle will ever hurry up.
I have kept bluegill for years. Use a hook with the barb pinched down and you should have no trouble in getting it to eat. Usually it takes them about a week or 10 days to get used to regular dry floating pellet food. Sunfish especially Green sunfish are often more aggressive than bluegill. The large mouth bass will probably give you trouble (mine did till i let it go) bass will not eat dry food of any kind and they will harrass everything in the tank. It should be kept alone or with another bass.
Do not put stink bait in your tank the one and only time i tried this it made the water cloudy and stank to high heaven. My maddtom eats shrimp pellets and it also will eat algae disks, cats usually eat what ever they can find.