Question

Why can sharks swim quickly through water

Answer 1

The reason why sharks can swim fast is that unlike most fish, sharks have tails that are not horizontally symmetrical . Instead , the top of a shark's tail protrudes further  back than the bottom , giving the shark  lift while swimming and making it "spring" forward at speed.

Most fish make a single water "ring"  that moves backward at the end of their tail's stroke but sharks are thought to produce two rings because of their asymmetrical  tail which bespeaks a more efficient propelling action.

It has also been discovered that sharks can raise the tiny teeth-like structures called placoid scales on their skin to create tiny wells across the surface of their skin  which reduces drag just like the dimples on a golf ball, thus enabling the shark move forward faster.