How old/how big is it? Oscars can enjoy a wide variety of foods. Pellets of course are great. Bloodworms, brine shrimp, beefheart, shrimp pellets, live crickets or earthworms... they'll eat just about anything. I shy away from pet store feeder fish for a host of reasons, though. Also, in my experience, they will almost always "act" like they are hungry, so just make sure that whatever you feed them to give appropriate amounts. If yours is still a juvenile, they can and will consume quite a bit; after all, they grow rather quickly for the first year. Use common sense with the amounts and the more variety the better. Good luck!