I read the list of the fastest animals on land at your site. But I was wondering what is the fastest animal in the sea might be?
According to Guinness World Records, the cosmopolitan sailfish is considered the fastest fish in the sea.
They point out that measuring a fish's speed over a short distance is very difficult to do. Still, in a series of speed trials carried out at the Long Key Fishing Camp in Florida, one sailfish took out 300 feet of line in three seconds, which is equivalent to a velocity of 68 mph.
—The Fact Monster