Lethrinus erythropterus
Uncommon but reliable on Koh Tao's reefs at 27-29C, with strong numbers off Palawan too, year-round.
Grows to around 35cm, with a silvery-grey body that shades to a soft pinkish tone along the flanks. The fins, especially the dorsal and tail, carry a reddish-orange wash that gives the species its common name. It has the classic emperor body plan: a sloped head profile and a single continuous dorsal fin, usually seen hovering just off the sand rather than tucked into coral.
Usually spotted cruising low over sand patches or rubble edges near reef, often alone or in loose small groups rather than tight schools. It tends to keep a cautious distance from divers, drifting off rather than bolting, and doesn't strongly associate with any one time of day in the logs. Look for it at the sandy fringes of reef rather than deep in coral structure.
Like other emperors, it hunts by picking invertebrates and small bottom-dwellers out of sand and rubble, which is why it's so often seen patrolling the reef edge rather than the reef itself.
No clear seasonal pattern shows up in the sighting data, and with water temperatures logged between 27.4 and 29.3C, it sits comfortably on tropical reefs all year. Plan around the destination's general dive season rather than a specific month for this species.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged around Koh Tao in Thailand, where it shows up on a large number of dive sites, and a strong second population off Palawan in the Philippines. Smaller but real sightings come from Nusa Tenggara and Raja Ampat in Indonesia, so it's worth watching for on Indo-Pacific reef and sand-patch dives generally.
Mapping where Longfin Emperor is logged…
Koh Tao in Thailand is the most consistent spot, logged across a large number of its dive sites. Palawan in the Philippines is also strong, with smaller numbers reported from Nusa Tenggara and Raja Ampat in Indonesia.
There's no detected season in the sightings, and it's found in warm water year-round (27.4 to 29.3C), so any time you're diving Koh Tao or Palawan is fair game.
Look for a silvery-grey fish around 35cm with a pinkish tone along the body and reddish-orange fins, cruising low over sand near the reef edge. The sloped head and single dorsal fin mark it as an emperor rather than a snapper.
They typically reach around 35cm, a medium-sized reef fish easily mistaken at a glance for one of the smaller snappers on the same reef.
No, they pose no threat to divers and typically move away rather than approach when you get close.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Emperor
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