Red Sea Surgeonfish

Acanthurus gahhm (Forsskål, 1775)

syn. Acanthurus gahm, Chaetodon nigrofuscus gahhm

50 cm1-40 mRed Sea endemicDangerousLeast Concern

1049

The name is literal. On each side of the tail base a surgeonfish carries a blade, and this is not a spine that happens to be sharp: it is hinged, it folds down into a groove where it sits flush with the body, and the fish flicks it out sideways and drives it home with a sweep of the tail. The edge is sharp enough to open a diver's hand to the bone, and the injuries that happen are almost all to people who grabbed one.

That is the entire danger. It does not attack anything, it is not venomous in this genus, and the blade exists for arguments with other surgeonfish over grazing ground.

This one is the big black surgeonfish of the 🌊 Red Sea, half a meter long, and it lives here and in the 🌊 Gulf of Aden and nowhere else. Reports from further east are almost always a different species being misnamed.

It is a grazer that also takes zooplankton and small animals, it moves with its pectoral fins like the rest of the family, and it works reef, lagoon and sand alike, sometimes alone and sometimes in loose groups.

The name gahhm is not Latin. It is the Arabic name for the fish on this coast, written down by Forsskal and made into a scientific name in 1789.

The genus. Acanthurus Forsskål 1775 - acanthus (thorn or spine) + oura (tail). ETYFish

The species. Acanthurus gahhm (Forsskål 1775) - Arabic name for this fish. ETYFish

How to recognise it

black to very dark brown body with a white ring around the tail base
yellow line around the eye and yellow tips to the pectoral fins
oval flattened body, moving on its pectoral fins rather than its tail
a fixed blade lying in a groove on each side of the tail base
up to 50 cm

Why it's threatened

Residential & commercial development

Housing & urban areas · Commercial & industrial areas · Tourism & recreation areas

Natural system modifications

Other ecosystem modifications

Acanthurus gahhm is associated with coral reef habitats. Urban growth, coastal land reclamation, fisheries expansions and water pollution combined with Crown of Thorns (COTS) outbreaks are placing increasing pressure on the coral reefs of the Red Sea and Gulf of Aden (Kotb et al. 2004). It is predicted that pressures on the reefs of the Red Sea and Gulf of Aden will increase over the next 8 years due to major development for mass tourism and industrialization, over exploitation, destructive fishing in poorly managed areas and COTS outbreaks (Kotb et al. 2004).

Surgeonfishes show varying degrees of habitat preference and utilization of coral reef habitats, with some species spending the majority of their life stages on coral reef while others primarily utilize seagrass beds, mangroves, algal beds, and /or rocky reefs. The majority of surgeonfishes are exclusively found on coral reef habitat, and of these, approximately 80% are experiencing a greater than 30% loss of coral reef area and degradation of coral reef habitat quality across their distributions. However, more research is needed to understand the long-term effects of coral reef habitat loss and degradation on these species' populations. Widespread coral reef loss and declining habitat conditions are particularly worrying for species that recruit into areas with live coral cover, especially as studies have shown that protection of pristine habitats facilitate the persistence of adult populations in species that have spatially separated adult and juvenile habitats (Comeros-Raynal et al. 2012).

Threat classification from the IUCN Red List.