Pomacentrus alexanderae
Small blue-grey damselfish logged mostly on Peninsular Malaysia's East Coast reefs, in warm 25.6-29C water, sightings uncommon year-round.
A small, deep-bodied damselfish that tops out around 6cm, so it reads as a quick grey-blue flicker against the reef rather than a showy fish. Look for a pale to greyish body with a faint dark blotch near the upper base of the tail and the typical damselfish silhouette: oval, slightly flattened, with a small pointed mouth. It stays close to coral heads or rubble patches, darting for cover rather than holding still for long looks.
Divers typically spot it hovering low over coral rubble or ducking into branching coral for cover, sticking close to a small patch of reef rather than roaming. It's a wary fish that tends to dart for shelter as divers approach rather than hold its ground, and logged sightings sit in the uncommon-to-rare range, so it takes a bit of looking rather than jumping out at you.
Like other Pomacentrus damselfish, it likely guards a small patch of reef against intruders, which is why divers usually see it hovering near one particular coral head rather than swimming freely across open reef.
No clear seasonal pattern shows up in the sightings, and the 25.6 to 29C temperature range it's found in matches these reefs year-round, so it's a fair bet on any visit to the East Coast of Peninsular Malaysia.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged on Peninsular Malaysia's East Coast, with a smaller but steady presence in Sabah, making Malaysia the strongest bet overall. It also turns up on reefs in Palawan and Luzon in the Philippines, with a single logged sighting at Koh Tao in Thailand.
Mapping where Alexander's Damselfish is logged…
It's most consistently logged on the East Coast of Peninsular Malaysia and in Sabah, Malaysia, with additional sightings on reefs in Palawan and Luzon in the Philippines.
There's no strong season in the sightings data, and it sits in warm 25.6 to 29C water year-round, so any time of year on the right reefs works.
Look for a small, deep-bodied damselfish around 6cm, greyish-blue overall with a faint dark mark near the top of the tail base, hovering close to coral or rubble.
They're a small reef fish, reaching around 6cm, so they're easy to miss among busier, brighter damselfish species on the same reef.
No, they pose no threat to divers and simply retreat into the reef structure when approached.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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