I usually use silversides, but just about any seafood should be fine. When I buy fish for myself, I usually give the anemone a piece. I've also fed it shrimp, clam, crab, krill (doesn't always like the krill), and my homemade fish recipe. The fresher the food, the better. I ge the best feeding response if what I'm feeding the anemone hasn't been frozen (not a necessity, though). You shouldn't have to put the food close to the mouth, but if the clown is getting to it before the anemone can get it in its mouth, it may be something to try. As far as size, I try not to feed mine anything much bigger than half the size of its mouth. I'm sure they can take bigger pieces, but I figure that's pretty safe.