DNA has proved 19th century scientists right – the surgeonfish Acanthurus nigros is a separate species and not a synonym of the Blueline surgeonfish, Acanthurus nigroris.
Where species of fishes (and other creatures) are very similar in appearance and morphology, taxonomists have historically had problems deciding whether or not they are distinct. Back in the early days it was common for every slight variation to be described as a separate species; then, as knowledge increased, many of these similar species were identified as one and the same, the first name used became the valid one, and the others were classed as synonyms.
Nowadays the new taxonomic tool of DNA study has helped confirm some of these decisions, but has also proved some of them wrong. An interesting case of this in marine fishes is the topic of a recent paper.
The Blueline surgeonfish, Acanthurus nigroris has for a long time been regarded as widespread in the central and western Pacific. It was described from Hawaii by the French ichthyologist Valenciennes in 1835, and some years later, in 1861, a similar species, Acanthurus nigros, was described by Günther from the New Hebrides (now Vanuatu). And thus matters remained for almost a century.
Then, in 1956, the well-known marine ichthyologist Jack Randall (also one of the authors of the new paper) revised the surgeonfish genus Acanthurus, declaring A. nigroris to be a valid species but regarding A. nigros as a synonym.
DNA study has now shown that the 19th century scientists were actually correct, and Acanthurus nigros has been revalidated as a distinct species. Its distribution extends from the Pitcairn Islands west to the Great Barrier Reef in Australia and the Caroline Islands, while its sister species A. nigroris is restricted to Hawaii and Johnston Atoll.
For further information see: John E. Randall, J.E., DiBattista, J.D. and C. Wilcox (2011) Acanthurus nigros Günther, a Valid Species of Surgeonfish, Distinct from the Hawaiian A. nigroris Valenciennes. Pacific Science, 65(2):265-275. 2011.
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