Billfish slash through fish schools with bills, then circle back to feed
A sailfish has been clocked at 110 kilometres an hour in a short burst, close to a cheetah's top speed and the fastest ever recorded for a fish. Its relatives the marlins and the swordfish share the same weapon: a long bony bill swung sideways through a school of prey like a club.
True billfish number just 12 species. The swordfish stands alone in its family, while the other 11, the marlins, spearfishes and sailfishes, make up a second. The swordfish's flat, sharp-edged bill can reach a third of its body length; the others carry shorter, rounder spears. Many billfish exceed three metres, the blue marlin can reach five, and females usually outgrow males.
The bill is mostly a slashing tool. A billfish charges into a school at speed, swiping left and right, then turns back to eat the stunned fish whole and head-first; adult swordfish have no teeth at all. Occasionally a marlin flips a fish up and spears it, and sharks such as great whites and makos have been found with broken bills lodged in them. When hunting, sailfish raise their enormous dorsal sail to herd prey, folding it away into a groove when cruising.
Like tuna, billfish combine efficient long-distance cruising with explosive sprints, and some keep their bodies several degrees warmer than the surrounding sea so their muscles work well in cold, deep water. Specialised swim bladders let them dive to the dim middle layers of the ocean and come back up quickly. Their speed poses a puzzle first raised in 1936 by the zoologist James Gray about dolphins: how can muscles deliver such power? Researchers in Taiwan proposed an aerodynamic explanation in 2009.
Billfish roam all oceans and follow currents and sea temperatures across such huge areas that scientists call them rare event species, which makes sustainable management hard. Fossils show that elongated snouts go back to the earliest Paleogene, with Hemingwaya from Turkmenistan among the oldest known.
Source: Billfish
