Acanthurus nigroris
A grey-brown reef surgeonfish with fine blue lines, logged as an uncommon find on Hawaii's reefs in 25-29C water year-round.
Grey to olive-brown body about the length of a dinner plate, marked with thin, close-set blue lines running along the flanks that catch the light as it turns. Like other surgeonfish it carries a small, sharp spine (scalpel-like blade) at the base of the tail, usually tipped in a paler colour. The tail fin is lightly forked, and the overall shape is the classic flattened, oval surgeonfish outline rather than anything showy.
Usually seen picking algae off rock and reef surfaces, often alone or in a loose scatter with other surgeonfish rather than tight schools. It keeps a working distance from divers, drifting off over the reef rather than bolting, and tends to stay low over structure while it grazes.
That tail spine is a real defensive weapon, it locks upright when the fish is threatened and can slice a careless hand, so admire the blue lines without reaching for the tail end.
Water temperatures at the sites where it's been logged run between about 25 and 29C, and there's no seasonal pattern in the sightings, so any time of year on Hawaii's reefs gives you a fair shot.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Every logged sighting in the data comes from Hawaii, United States, making it the only confirmed region to plan a dive around this species. Within Hawaii it turns up on reef sites at a uncommon rate, so treat it as a nice surprise rather than a guaranteed encounter.
Mapping where Bluelined Surgeonfish is logged…
The only confirmed sightings in the data are from Hawaii, United States, where it shows up on reef sites as an uncommon but real find.
There's no clear season in the sighting data. Water in its Hawaiian habitat sits between roughly 25 and 29C year-round, and the fish appears to be present on the reef throughout that range.
Look for a grey-brown, oval-bodied surgeonfish around 18cm long with fine blue lines running along its sides and a small pale-tipped spine at the base of the tail.
They typically reach around 18cm, putting them at the smaller end of the surgeonfish family and easy to overlook against a busy reef.
No. They pose no threat to divers under normal conditions, though like all surgeonfish they carry a sharp tail spine used only in self-defence, so it's best not to grab or corner one.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Striped Surgeonfish
3,294 sites
