The common name "surgeonfish" is derived from a characteristic that clearly distinguishes Acanthuridae from other fish families: the spines or "scalpels" on the caudal peduncle, one or more on each side. Based primarily on differences in this characteristic, the family can be divided into three subfamilies: The Acanthurinae, in which the peduncular spine rests in a groove and can be erected in defence during the fights, the Nasinae and Prionurinae in which the peduncular feature is arranged as one or more fixed blades on each side, that are sharp and elongate with age.
Place of origin:Central Pacific
Achilles Surgeon, Acanthurus achilles can be found in various Pacific Ocean localities, including Micronesia to Hawaiian Islands, New Caledonia and as far as the Marquesas, but is especially abundant in Polynesia Island region. Occurs primarily on exposed shallow reef flats. Adults are readily recognised by the large bright orange patch on the rear of the body, covering the peduncular spine. Acanthurus achilles hybridises with A.nigricans and this form was named A.rackliffei. Length to 23 cm.