Ideas on feeding Rainbow Sharks?

Hello, my Rainbow Shark usually eats with the lights closed, so i cant see him eat. I saw him once at the pet store like 3 years ago, but if i feed him with the aquarium lights on will he come out of his cave and eat. I feed him frozen brine shrimp.Also another question, what do you think is better, frozen bloodworms, frozen brine shrimp, or a frozen dead fish for him to eat, my pet store sells all of them and they said that the Rainbow Shark will enjoy all but which do you prefer?