I would for sure say that one good Chromis or damsel would be fine, but these shrimp are small and I don't think they contain near the nutritional value. My feeding is like once every 5 days, but it still seems like twice a week. All I know is that my angler has grown 16x as large as when I got him so I think he's healthy. My angler will refuse food once he is full. Usually 10-15 go to him and 5-10 are eaten by damsels and my 54 gallon members.
Bottom line, if he gets a good meal, I'd say once per week is plenty.