feed him what he eats in the wild, shrimp, w/ shell on (little chunks), white fish chunks, crab meat, silverisdes (I know you said he does eat them, but he will) Mysid shrimp.
IMO krill is like a potato chip. you can eat chips for a while, but they aren't all you can eat and worse much of the krill products have been freeze dreid or reduced and they lack important nutrients