Fastest fish
Bluefin tuna, Thunnus thynnus, Sailfish, Istiophorus platypterus
125.5; 231.7 kilometre(s) per hour
Not Applicable ()

Two species are frequently cited as prime contenders to be the fastest fish, although it is notoriously difficult to obtain accurate measurements under natural conditions. As reported on 31 May 2015, the Central American Billfish Association based at the University of Miami, Florida, USA, recorded tracked sailfish (Istiophorus platypterus) accelerating at a g-force of 1.79 g, the equivalent of 78 mph (125.5 km/h). A 2015 study by the Large Pelagics Research Center in Gloucester, Massachusetts, USA, meanwhile, proposed another species: the bluefin tuna (Thunnus thynnus), with one tagged specimen tracked near Port Mouton in Nova Scotia, Canada, recording an acceleration of 3.27 g. If this rate were maintained for just two seconds, it would equate to 144 mph (231.7 km/h). However, both these measurements reflect brief bursts of acceleration rather than maximum speeds attained and sustained.

The sailfish’s common name is inspired by its large dorsal fin, which sometimes extends the full length of its body. The fin may be folded down for increased streamlining and manoeuvrability.

During speed trials carried out some time between 1910 and 1925 at the Long Key Fishing Camp in Florida, USA, a specimen of sailfish reportedly took out 300 ft (91 m) of line in 3 sec, which was equated to a velocity of 67.7 mph (109 km/h). However, this was an estimate, and no known definitive evidence from that time remains to support it.