Longest fin

All three species of thresher shark (family Alopiidae) have a huge scythe-shaped caudal fin (tail fin) which is roughly as long as the body itself. The largest and commonest species, Alopias vulpinus, found world-wide in temperate and tropical seas, may grow to a length of 6 m (19 ft 8 in) of which almost 3 m (9 ft 10 in) consists of this greatly elongated upper tail fin; the body itself is rather sleek and relatively small. The thresher is believed to use its extraordinary tail to herd and then stun schools of milling fish ready for eating (although this behaviour is speculative and has never been observed in the wild).