Sohal surgeonfish

The sohal surgeonfish (Acanthurus sohal) or sohal tang, is a species of marine ray-finned fish belonging to the family Acanthuridae, which includes the surgeonfishes, unicornfishes and tangs. This fish is found in the northwestern Indian Ocean.

Taxonomy
The sohal surgeonfish was first formally described in 1775 as Chaetodon sohal by the Swedish-speaking Finnish naturalist, explorer and orientalist Peter Forsskål with its type locality given as the Red Sea. Forsskål proposed Acanthuirus as a subgenus of Chaetodon although he recognised that it was probably different from Chaetodon even at the family level.In 1856 Desmarest designated Teuthis hepatus, which had been described from a type now known to have been collected at Ambon Island in the Moluccas (other erroneous type localities were named) in 1758 by Linnaeus, as the type species of the genus. T. hepatus is a synonym of Paracanthurus hepatus and this would make Paracanthurus synonymous with Acanthurus. An alternative would be to use the name Harpurus proposed as a monospecific genus in 1788 by Johann Reinhold Forster when he described Harpurus fasciatus, a synonym of Acanthurus triostegus. It has been proposed that the International Commission on Zoological Nomenclature should be petitioned to stabilise the genera Acanthurus and Paracanthurus. In 2014 it was proposed that the type species of Acanthurus should be C. sohal, which had also been described by Forsskål in 1775 as a member of the subgenus alongside C. bifasciatus, C. nigrofuscus and C. unicornis, and had been designated as the type species by Jordan and Evermann in 1917. The genus Acanthurus is one of two genera in the tribe Acanthurini which is one of three tribes in the subfamily Acanthurinae which is one of two subfamilies in the family Acanthuridae.

Etymology
The sohal surgeonfish's specific name, sohal, is the Arabic name for this species along the Red Sea coast.

Description
The sohal surgeonfish has its dorsal fin supported by 9 spines and 30 or 31 soft rays while the anal fin is supported by 3 spines and 28 or 29, typically 29, soft rays. The depth of the body is around half the standard length. This fish has longitudinal, thin black stripes separated by greenish olive stripes and these join together at the spine on the caudal peduncle. The stripes are finer and more sinuous on the upper body but broader and straighter on the lower body. The stripes are greyer on the upper head and nape. The lower head and ventral surface of the body are pale with faint grey and greenish grey longitudinal lines> the dorsal, anal and pelvic fins are black with vivid blue margins, there is a large patch of orange on the body underneath the pectoral fin and the sheath of the spine on the caudal peduncle is orange. The caudal fin is lunate. This species has a maximum published total length of 40 cm.

Distribution and habitat
The sohal surgeonfish is endemic to the northwestern Indiian Ocean where it is found in the Red Sea, east along the coast of the Arabian Peninsula to the Persian Gulf. It has been found in the Mediterranean Sea, in 2017 and 2018, and reached there either by release from an aquarium or by Lessepsian migration through the Suez Canal from the Red Sea. It is usually found on the outer edges of fringing reefs that are exposed to surge, typically down to depths of around 20 m.

Biology
The sohal surgeonfish may be encountered either singly or in small schools and is known to be very territorial. The spine on the caudal peduncle has been reported to bear venom. It grazes on algae growing on hard substrates and despite being solitary they will school to graze in the territories of other fishes. The territory guards food resources and the territory holder may shelter and otherwise spend a lot of time out of its territory or patrolling its boundaries.

Utilisation
The sohal surgeonfish is targeted by fisheries as a food fish and is also traded in the aquarium trade.