The orange spotted filefish / Oxymonacanthus is very, very difficult to keep and do not live long in captivity. They require a diet of Acropora, if you can get this fish on prepared foods, you can feed a blend of Meaty foods plus greens, unfortunately this rarely happens in captivity.
If we are talking about orange spotted / Cantherhines filefish they can get to eight inches and require a variety of meaty foods plus greens.
This is where a common name can be confusing........ LOL
Do you have a picture?
Kaye