here is the part from Fenner's book.
Powder Brown and White-faced Tangs
Acanthurus nigricans, A.japonicus
WHEN SHAKESPEARE ASKED, "What's in a name?" he could hardly have had the surgeon fishes in mind, but there is plenty of drama-both comedy and tragedy-when it comes to the common names of these species. Can you tell me which three species are called "blue" tangs? (At least the Adantic Blue Acanthurus coeruleus; the fabulous Powder Blue, A. leucosternon; and the Indo-Pacific Blue Paracanthurus hepatus. The last is variously called the Hippo, Yellow-tail Blue, Regal, and Palette Tang.) How many "sailfin" tangs do you know? If there ever was an argument for using scientific names rather than common names, it's here in the tangle of everyday surgeonfish nomenclature.
Consider, for example, two very similar-appearing species of surgeons whose common and scientific names are all too often interchanged in the trade. For purely intellectual reasons this misidentification might bother you, but there is more to it. The two species in question look alike, yet are very different in their likeliness to do well in captivity. Based on handling hundreds of specimens, I'd peg their relative potential at aquarium survival for more than three months at a hundred times more likely for one than for the other. Both are sold under the common name Powder Brown Tang.
Acanthurus nigricans, which we will call the Powder Brown Tang, is an over all varying brown with a white patch under the eye. The dorsal, anal, and ventral fins are black with blue edges. The base of the dorsal and anal fins is graced with a brilliant yellow; their tails are white with a vertical yellow bar.
Acanthurus japonicus which we'll refer to as the White-faced Tang, is similarly marked and colored, with the following notable differences: the White-faced Tang is adorned with a red stripe on its dorsal that starts one third of the way back and extends to the end. Note the white patch under the eye; it's larger in A.japonicus, extending all the way to the mouth, hence the common name White-faced-some- times White-cheeked. (To confuse the issue, some sources give A. nigricans the name White-cheeked Tang.)
The body shape of the White-faced is decidedly more oval than that of the Powder Brown, but, realistically, 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-very beautiful, in fact, when healthy and shown under proper lighting. Ah, but one is a historically poor feeder, all too often dying within a few weeks of purchase. The other is a very hardy and desirable aquarium species.
Both are often sold as Powder Browns, often for similar cost, and there indeed, is the rub. Yes, you do want to know how to tell one from the other, so you can purchase the White-faced A.japonicus, and avoid the real Powder Brown, A. nigricans.
The Powder Brown is widely distributed over the vast mid-Pacific area called Oceania, including Hawaii; it is also found along the East Pacific from Baja to Panama. Its range overlaps that of the White-faced Surgeon in parts of the tropical Indo-Pacific, but displaces it between New Guinea and Australia. Sources are important: for the true Powder Brown species, if you must try one, get it from Hawaii, Tonga, christmas Island or the Marshall Islands, not the Philippines or Indonesia.
One of the most frequently encountered queries we hear in the pet-fish industry touches on the ethics of what is offered. Why do "they" offer (the organism in question) under different names, knowing that (the organism in question) doesn't do well under captive conditions?
After many years in the aquatic nature business I can assure you that:
1) No, it's not some grand conspiracy to cheat the Western consumer;
2) No, it's not a mean-spirited lesson meant to impress the diminishing value of the dollar on you;
3) Yes, it is a problem directly traceable to the state of sophistication of the collectors, shippers, wholesalers, retailers, and other go-betweens. That is, it's about as good as we all can do collectively, at this point;
4) We all, as consumers, are/have been willing to pony up our hard- earned cash for whatever is offered, without trying to become informed ahead of time.
I don't like the waste and inefficiency, and I don't think you should either. Become a more intelligent consumer and cast your votes/dollars for livestock that lives. Make a choice in favor of the White-faced Tang, A.Japonicus. If placing a special order, be sure to use the scientific name. If you don't know how to identify the species by sight, bring along a visual reference when the fish is ready to be picked up.
