Sail Fish
Scientific name Istiophorus platypterus
The Sailfish is one of the fastest fish in the ocean — a true pelagic predator built for speed. Instantly recognisable by its enormous sail-like dorsal fin and long, spear-shaped bill, this sleek hunter is designed for life in open water.
Around Koh Tao and the Gulf of Thailand, Sailfish are rare but unforgettable encounters. They are typically seen offshore in blue water, often near bait balls or areas where currents concentrate schools of smaller fish. Sightings usually happen on deeper pinnacles or during blue-water dives, and they tend to appear suddenly and disappear just as quickly.
Their tall dorsal “sail” can be raised to herd baitfish into tight balls, making hunting more efficient. Combined with explosive acceleration and precise movements of their bill, Sailfish are incredibly effective predators.
Although they can grow over 3 metres in length (including the bill), they pose no threat to divers and generally keep their distance.
Find Sail Fish at...
Divemaster's tip
If you spot one, stay calm and avoid sudden movements.
Keep your eyes on the blue — Sailfish often cruise just beyond the reef edge.
Have your camera ready — encounters are usually brief.
What do they eat?
Sailfish feed primarily on small schooling fish such as sardines, anchovies, and mackerel, as well as squid.
By targeting fast-moving baitfish in open water, they play a key role as apex predators in offshore ecosystems — a true symbol of speed and power in the Gulf.
