Chrysiptera unimaculata
A shallow-reef regular from Phuket to Marsa Alam, uncommon but reliable in water around 25-29C year-round.
Small, deep-bodied damselfish around 7 cm, usually dark brown to grey-black overall with a single pale white or bluish spot near the base of the tail, which is the feature to key on. The body shape is typical damsel: oval, laterally flattened, with a small mouth built for grazing algae off rock and coral. Juveniles tend to show the tail spot more vividly against a darker body, fading slightly with age.
Look for it hovering close to the reef in the shallows, rarely straying far from a patch of rock or coral rubble where it grazes on algae. It's a fairly unremarkable presence compared to its more territorial damselfish relatives, tolerating divers at a reasonable distance rather than darting for cover or attacking. Most sightings come from depths under 3 metres, so it's a fish you'll notice while finning over the shallow reef flat or during a snorkel rather than on a deep drift.
Despite belonging to a family famous for feisty, territorial behaviour, it's logged as uncommon at the vast majority of sites where it's seen, suggesting it keeps a lower profile and smaller patch size than bolder damselfish species.
No clear seasonal pattern shows up in the sighting data, and with a comfortable range of roughly 25 to 29C it's present on shallow reefs year-round rather than tied to a particular month.
Most reliably found in Thailand, with strong numbers around Phuket and Koh Lipe, and also a steady presence in the Egyptian Red Sea around Marsa Alam and the Deep South. Further sightings come from Java and Bali in Indonesia, the Central Atolls in the Maldives, and the Andaman Islands in India, so it turns up widely across shallow tropical reef systems in the Indo-Pacific and Red Sea.
Mapping where Onespot Damselfish is logged…
Thailand is the strongest bet, particularly Phuket and Koh Lipe, followed by Egypt's Marsa Alam and Deep South region. It also shows up in Indonesia (Java, Bali), the Maldives' Central Atolls, and India's Andaman Islands.
There's no strong seasonal pattern in the data, so it's a year-round sighting on shallow tropical reefs where water sits between about 25 and 29C.
Look for a small, dark brown to blackish damselfish around 7 cm long with one pale spot near the base of the tail. It stays close to shallow reef structure, usually under 3 metres, grazing on algae.
They're small, typically reaching around 7 cm in length, in keeping with most damselfish species.
No, they pose no danger to divers. They're small herbivores that graze algae off the reef and generally tolerate divers without aggressive behaviour.
They're usually logged as uncommon at the sites where divers find them, rather than being a guaranteed sighting, though a handful of sites report them as common.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Yellowtail Clownfish
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