Pseudobalistes flavimarginatus
Meet the yellowmargin triggerfish on reefs in the Maldives' Central Atolls or Egypt's Marsa Alam, in water around 25-29C year-round.
Safety warning
Give nesting females a wide berth: they dig a crater nest on the sand and will charge and bite divers who get too close, and that bite from a triggerfish this size can break skin. If one starts swimming at you head-on or flaring its dorsal spine, back away calmly rather than turning your back on it.
If you're bitten
Territorial biteGeneral first-aid guidance, not a substitute for professional medical care. In an emergency, call your local emergency number.
A big, deep-bodied triggerfish with an olive to grey-brown body and a thin bright yellow margin tracing the dorsal and anal fins, which gives it its name. Look for pale, almost white lips and a faint dark patch near the base of the pectoral fin. Adults reach around 42 cm and have a heavy, slab-sided look compared with slimmer reef fish, with the small first dorsal spine ('trigger') that locks upright when the fish feels threatened.
Usually seen alone, cruising slowly over sand patches or reef flats while it noses around for food, often flipping over rubble or urchins to get at what's underneath. It tends to hold its ground rather than bolt when divers approach, watching you as much as you watch it, though it gets noticeably more defensive near a nest site. Most sightings are on open reef and lagoon edges rather than deep drop-offs, matching its wide but shallow-leaning depth range.
Females guard a nest of eggs laid in a sandy crater on the seabed and will fan and defend it aggressively, which is when this normally unbothered fish turns territorial.
No clear seasonal pattern shows up in sightings, and it sits comfortably in water from about 25 to 29C, so it's a year-round find on tropical reefs across its range.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged in the Maldives, especially the Central Atolls and Northern and Southern Atolls, and a strong presence through Egypt's Marsa Alam and the Deep South. It also turns up regularly on Malaysia's Peninsular East Coast, around Koh Tao and Khao Lak in Thailand, and in Indonesia, French Polynesia's Society Islands, the Philippines and Timor-Leste.
Mapping where Yellowmargin Triggerfish is logged…
The Maldives is the most consistent place, particularly the Central, Northern and Southern Atolls, alongside Egypt's Marsa Alam and Deep South. Malaysia's east coast, Koh Tao and Khao Lak in Thailand, and French Polynesia's Society Islands are also solid options.
There's no strong season in the sighting data, and it lives comfortably in 25-29C water, so it's seen year-round on the reefs where it occurs.
They can be, mainly around nest sites where a guarding female will charge and bite divers that get too close. Away from nests they're generally calm and simply watch divers rather than react.
Look for an olive-brown, deep-bodied fish around 40 cm with a fine yellow edge along the dorsal and anal fins and pale, whitish lips. It moves slowly over sand and rubble rather than darting like smaller reef fish.
They typically reach around 42 cm in length, making them one of the larger triggerfish divers encounter on tropical reefs.
Females dig a crater nest in the sand to lay their eggs and guard it fiercely, turning an otherwise unbothered fish into one of the more defensive animals on the reef.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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