What is the fastest marine animal?

The black marlin is the fastest sea animal by far. With a streamlined physique and a rigid pectoral fin to cut through water, it showcases evolutionary perfection for speed. This apex predator capitalizes on its velocity to overtake even the swiftest prey, such as tuna and flying fish. Its bill is used as a weapon for hunting, to slash through schools of fish in an attempt to stun or injure prey before circling back to eat them. This method allows the marlin to target multiple potential prey in a single pass, increasing its chances of a successful hunt.

Source: Ultimate Kilimanjaro