Not only it can eat fish but this one of the most especialazed turts in caching fish. That´s why they have that worm like protuberance in the tounge ,to lure fish into its bone crushing jaws. This guys are super predators
I think the question is "What can't an Alligator Snapping Turtle eat?"
I'm joking, but just barely. In nature they eat mostly fish, but also crayfish, amphibians, smaller turtles, ducklings - just about anything smaller than them. You could possibly have a problem feeding live catfish because of spines, but I doubt it.
I have a Common Snapping Turtle. I feed him mostly pellets and earthworms, plus guppies and feeder goldfish. I have fed him market shrimp and even scallops as well. Catfish fillets are pretty cheap, I may feed him some once in a while.
I think they are really asking if they can eat a CATfish. Yes they probably can but I wouldn't feed it to them because they have the spines that I wouldn't want to risk getting stuck in the turtle's throat.
A little off topic but I was at this one small private reptile zoo when I was a kid and they had a huge Alligator Snapper that lived with a pair of Spectacled Caiman. I guess they left each other alone but still I wouldn't trust that gator snapper.
What? I want them gone, they're destroying the natural wildlife. This is the lowest lizard, snake, and bird population we've ever had. It's better than taking them to the local Chinese restaurant.