Chaetodon adiergastos
Spot this grey-scaled butterflyfish on reefs in Sulawesi, the Visayas and Sabah at 27-29.5°C, year-round on tropical reef slopes.
A grey to silvery body crossed with fine dark diagonal lines gives it a scribbled, cross-hatched look rather than bold blocks of colour. A black band runs through the eye and a second dark bar sits near the tail base, with a yellow-tinged rear fin. At around 14 cm it is a small, disc-shaped reef fish, usually seen alone or in pairs picking along the reef face rather than schooling.
Divers typically find it working reef slopes and coral heads solo or in loose pairs, nosing into crevices and coral branches for food rather than hovering in open water. It sits at the uncommon end of the sighting scale at most sites, so treat any encounter as a nice find rather than a given, and expect it to keep a cautious distance rather than approach.
Like most butterflyfish it pairs up and holds a patch of reef, so seeing two together on the same coral head over repeat dives is often the same bonded pair rather than a coincidence.
No strong seasonal pattern shows up in the data, and with a water-temperature niche of 27 to 29.5°C it stays comfortable on tropical reefs all year, so any month works for a sighting.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
This is a Coral Triangle regular, most consistently logged in Indonesia and the Philippines, with particularly strong numbers in the Visayas, Sulawesi, Luzon and Palawan. It also turns up reliably in Sabah, Malaysia, and shows up in smaller but real numbers across Thailand, Australia, Vietnam, Cambodia and Brunei.
Mapping where Philippine Butterflyfish is logged…
Best chances are on Coral Triangle reefs, especially the Visayas, Palawan and Luzon in the Philippines, Sulawesi and Bali in Indonesia, and Sabah in Malaysia. It also appears in smaller numbers in Thailand, Australia, Vietnam, Cambodia and Brunei.
There is no clear seasonal pattern in sightings, and it lives in a narrow warm range of 27 to 29.5°C year-round, so it is a fair bet on any dive month in its Southeast Asian range.
Look for a small grey-bodied butterflyfish, about 14 cm, covered in fine crosshatched dark lines with a black eye-stripe and a dark bar near the tail. It usually swims alone or in a pair close to the reef rather than in a school.
They reach around 14 cm in length, a typical small size for a reef-associated butterflyfish.
No, they pose no threat to divers and simply forage over the reef, keeping their distance if approached.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
