How big can a thresher get?
Thresher shark
6.1 metres
Named for their exceptionally long, thresher-like heterocercal tail or caudal fins (which can be as long as the total body length), thresher sharks are active predators; the tail is used as a weapon to stun prey. The thresher shark has a short head and a cone-shaped nose. The mouth is generally small, and the teeth range in size from small to large.[6] By far the largest of the three species is the common thresher, Alopias vulpinus, which may reach a length of 6.1 metres (20ft) and a weight of over 500 kilograms (1,100lb). The bigeye thresher, Alopias superciliosus, is next in size, reaching a length of 4.9m (16ft); at just 3m (10ft), the pelagic thresher, Alopias pelagicus, is the smallest.