from wet web media....heres an article you should def read, link at the bottom.
'Acanthurus (glaucopareius) nigricans (Linnaeus 1958), the Powder Brown or Gold-Rimmed Surgeon (and Whitecheek Surgeon to science), Cat Tang in Hawai'i.... The corrected scientific name of this species is A. nigricans (per Randall, 1988); a revision no doubt as unpopular to some as my labeling the species as "bad". The very similar A. japonicus is a far better aquarium fish; A. nigricans rarely lives for more than a few months in captivity, often, oh joy, bringing in parasitic Protozoan disease to take the rest of your fish livestock with them.
Acanthurus japonicus ("Ah-kan-thur-us ha-pawn-ick-us") will refer to as
the white-faced surgeon/tang is similarly marked and colored with the following notable differences. The white-faced tang is adorned with a red stripe on it's dorsal that starts one third back and extends to the end. Check out the white patch under the eye, it's larger in
A. japonicus, extending all the way to the mouth, hence the name white-face (sometimes white-cheek). Body-shape wise the white-face is decidedly more oval than the powder brown as well, but you tell me, could you tell these two apart if you didn't have both on hand for comparison? And what's the big deal anyway? They're both good looking......
full link, def worth reading a couple of times....
A. nigricans &A.japonicus