This is definately a tang/surgeon/doctorfish (all the same common name) of the genus Acanthurus. It is obviously not one of the popular imported more colorful species. The problem in identifying this little guy to the species level for sure is that...
1. There are some 40 species within the Acanthurus genus, which includes a few versions of "mimic tangs". A few of those species are well known in the aquarium trade due to their good looks. The rest are for the most part more drabbly colored.
2. Among the Acanthurus there are regional differentiations within each species, adding to the confusion in identifying the more drab individuals.
3. There are also color and pattern differences according to age and stage of development.
What does this all mean? It'll be damn hard to get a species name on this guy. Try and ask the store you got him at where he came from. If the owner does not know his distributor may, unless he gets his fish direct, which is unusual...
By the way I don't think it is in the Ctenochaetus genus (ex. kole tang), but that is easy to tell when you look at his mouth while feeding. Anyway good luck... pictures probably won't get you any further than you are right now... but there may be someone out there who could help further, but I've seen many tangs, and that's my 2 cents... Whatever you do... keep it
