small aros do best with crickets, mealworms, and carnivore sticks. as they grow they can take larger stuff like superworms, nightcrawlers, and cut fillets. when even larger you can start feeding whole shrimp, prawns, smelt, silversides, fillets, etc.
feeder fish is never recommended unless you're breeding your own
it's sometimes tricky to get small aros to accept a variety of foods. try different things and see what he likes.