Longfin Bannerfish
Scientific name Heniochus acuminatus
Bannerfish are elegant, high-contrast reef fish instantly recognised by their bold black-and-white bands, yellow highlights and long trailing dorsal filament that waves like a banner in the current.
Around Koh Tao, they are commonly seen in pairs or small schools hovering above coral slopes and pinnacles. Their graceful, synchronized swimming and clean colour pattern often make them stand out clearly against the reef backdrop.
They are sometimes mistaken for Moorish idols, but bannerfish are generally more common locally and often gather in groups rather than staying strictly in pairs. Their long dorsal “banner” is not just decorative — it may help with species recognition and schooling behaviour.
Bannerfish are active daytime feeders and are comfortable in moderate current, often seen facing into the flow as they pick food from the water column or reef surface.
Their presence adds movement and contrast to Koh Tao’s dive sites, especially on vibrant reef walls and mid-water pinnacles.
Find Longfin Bannerfish at...
Divemaster's tip
Look slightly above the reef rather than directly into it. Bannerfish often hover in mid-water between 5–20 metres, especially where there is light current.
If you remain still, schools may circle gently around you — a beautiful photographic opportunity.
What do they eat?
Bannerfish feed on zooplankton, small crustaceans and occasionally coral polyps.
They often position themselves in current to capture drifting plankton, using quick, precise movements to snap up food from the water column.
