The fastest fish in the sea
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Sometimes an animal is so fast even the record books can’t keep up! In this second installment of ‘Behind the speed,’ we journey away from the land into the ocean, to uncover the anatomical secrets of one of nature’s greatest speed demons; the Atlantic sailfish.
In pursuit of the title for ‘fastest animal on the planet’ is a fish whose agility and speed pips even a sprinting cheetah to the finishing line. 
With its long circular bill and elongated body, the sailfish’s striking profile makes it a predator created for speed. A master of stability and solidity, the sailfish achieves unbelievable speeds while remaining perfectly on target. Considering the fact that water is over 750 times denser than air, these fish are effectively overcoming greater resistance than to their four-legged feline friends. Which is quite a feat!
At first sight, their erect dorsal fin may look unwieldy, but the characteristic sail-like form can be sleekly folded into a groove in its back - hydrodynamic at the drop of a hat. This piece of apparatus is also used to prevent rolling or yawing after a burst of speed, as well as effectively striking fear into its prey, by making the fish appear much larger than it actually is. Groups of sailfish have even been observed using them tactically to herd schools of fish and squid into ‘bait balls’.
Read the full story on the BBC Earth blog.
