It depends on the type of cat fish. If you know the type you can look it up on the web. Many learn to eat flakes from the surface, and will do so no matter what you provide on the bottom of the tank. Some catfish also will swallow air for various reasons. In general catfish tend to act weird.. . As far as what to feed it. The ones with sucker mouths generally prefer plants, but will eat anything off the ground. You can buy algae disks for them, or try cumber slices. Those without sucker mouth prefer sinking pellets made of fish, or worm.