Diagramma melanacrum
Blackfin Sweetlips are a reliable sighting on Sabah's reefs in Malaysia, hovering in warm 28C water year-round.
Grows to around 31cm, with a stocky, deep-bodied shape typical of sweetlips and a pale grey to silvery flank that darkens toward blackish fins, which is the easiest tell underwater. The face and lips have a slightly fuller, rounded profile than slimmer grunts, and the tail and dorsal fin often look almost black against the lighter body. Usually seen singly or in small loose groups hovering just off the reef rather than out in open water.
Typically found hanging motionless in the shade of overhangs, coral bommies, or under jetties during the day, doing little to acknowledge passing divers. Sweetlips in general become more active foragers over sand and rubble patches after dark, and blackfin sweetlips likely follow the same pattern, tucking back under cover by daylight. Approached slowly it tends to sit tight rather than bolt, making it an easy fish to get a good look at without rushing.
Like other sweetlips, this species is a nocturnal hunter that spends daylight hours resting near reef structure and becomes far more active feeding on invertebrates once the sun goes down.
No clear seasonal pattern shows up in the data, and with water sitting steadily between 27.9 and 29C it's a year-round presence on these tropical reefs rather than a seasonal visitor.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably found on reefs in Sabah, Malaysia, where it turns up across a wide spread of sites and counts as common at over half of them. It has also been logged in Raja Ampat, Indonesia, though far less frequently, so Sabah is the stronger bet for a planned sighting.
Mapping where Blackfin Sweetlips is logged…
Sabah, Malaysia is by far the most consistent place to find them, with sightings logged across a wide range of sites there. A smaller number have also been recorded in Raja Ampat, Indonesia.
There's no strong season in the sightings data, and warm 28C-ish water year-round means they're a reliable find on Sabah's reefs at any time of year.
Look for a stocky, deep-bodied fish around 30cm with a pale grey body that darkens sharply toward near-black fins, usually resting motionless near reef structure rather than swimming in the open.
They typically reach around 31cm, a mid-sized member of the sweetlips family, so don't expect the bulkier proportions of some larger sweetlips species.
No, they pose no danger to divers. They're calm, reef-associated fish that tend to hold their position rather than react defensively when approached.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Bluestriped Grunt
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