Which animal is the fastest swimmer?

The black marlin is frequently named the fastest swimmer in the ocean, with reported burst speeds of around 130 kilometres per hour, though such extreme figures are debated among scientists. The sailfish is another strong contender, capable of roughly 110 kilometres per hour in short bursts and famous for raising its huge dorsal fin like a sail. These billfish have streamlined bodies and powerful crescent-shaped tails that let them accelerate rapidly to hunt or escape. Among marine mammals, dolphins and orcas can sustain speeds over 50 kilometres per hour, using far less energy per stroke thanks to their smooth, drag-reducing skin.