Plectorhinchus gibbosus
Bulky, dark grunt often overlooked on Seychelles reefs and Thailand walls, comfortable in warm 25-29C water year-round.
A heavy-bodied, almost humpbacked grunt that grows to around 52cm, with a uniform dark brown to blackish body that can look almost charcoal in low light. The steep forehead profile and thick lips are the main giveaways, since it lacks the bold spots or stripes of other sweetlips. It often hangs close to the reef structure rather than out in open water, which combined with its dull colouring makes it easy to swim past.
Usually found resting or hovering low near coral heads, ledges and reef structure rather than cruising open water, often solo or in loose small groups. It tends to be unhurried around divers, holding position under an overhang until you get fairly close before easing away. Most sightings are logged during daytime reef dives in the 8 to 25m range, where it blends into shadow against dark coral and rock.
Its plain, almost featureless dark colouring is unusual for the sweetlips family, most of which rely on bold spots or stripes, so it is often misidentified simply because divers expect a flashier pattern.
Sightings run year-round, no clear seasonal peak shows up in the data, which fits its comfort range of roughly 25 to 29C on tropical reefs. Plan around the dive season for your chosen region rather than a specific month for this fish.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged in the Inner Islands of Seychelles, with strong numbers also around Phuket and Chumphon in Thailand and along the Sihanoukville coast of Cambodia. It also turns up on reefs in Queensland, Australia, in the Central Atolls of the Maldives, and around West Papua in Indonesia.
Mapping where Black Sweetlip is logged…
The Inner Islands of Seychelles are the most consistent spot, with good numbers also around Phuket and Chumphon in Thailand and the Sihanoukville coast of Cambodia. Reefs in Queensland, Australia, and the Maldives' Central Atolls also produce regular sightings.
There is no strong seasonal pattern in the sightings, so it is considered a year-round fish on tropical reefs where water stays between about 25 and 29C. Time your trip around good diving conditions for the region rather than a specific sweetlip season.
Look for a heavy-bodied grunt up to about 52cm with an almost uniform dark brown to blackish body and a steep, humped forehead. Unlike many sweetlips it has no bold spots or stripes, so it can look like a plain dark shadow near reef structure.
They typically reach around 52cm in length, making them a solidly built, medium-large reef fish rather than a small one. Divers usually spot adults at this size resting near coral structure rather than out in open water.
No, they are not considered dangerous to divers and show no aggressive behaviour toward people on the reef. They typically hold position under ledges and ease away calmly if you approach too closely.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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