A dark blue fish to 3.4 m (11 ft) with a long thin bill and a dorsal fin so large it is called a sail, folded flat into a groove when the fish is traveling and thrown up when it is not.
The sail is a hunting tool. Sailfish work baitfish schools in groups, raising their fins to make themselves look enormous and herding the school into a tight ball at the surface, then taking turns to slash through it with the bill. It is coordinated, the fish take turns rather than colliding, and the bill is used to stun rather than to spear.
While they do it they change color. Bars of pale blue flash on and off along the flanks within a second, driven by pigment cells under direct nervous control, and the flashing is aimed at the other sailfish rather than the prey - a way of signaling intent so two animals do not slash into each other.
About the speed record: the famous 110 km/h figure comes from a 1940s fishing-line experiment and has not survived scrutiny. Careful measurements put a sailfish's real burst at around 35 km/h, which is fast but not the fastest fish in the sea, and the bill's acceleration at the tip is what does the actual work.
The genus. Istiophorus Lacepède 1801 - istios (sail) + phorus (bearer). ETYFish
The species. Istiophorus platypterus (Shaw 1792) - platy (broad) + pterus (fin). ETYFish
- enormous sail-like dorsal fin, far taller than the body is deep
- long thin bill and a stiff crescent tail
- dark blue back with pale vertical bars that flash on and off while hunting
- length up to 3.4 m
