How is the shape of a shark's body adapted for swimming?

Their bodies taper to points at both the snout and the tail, reducing water resistance. Also decreasing drag -- and therefore noise -- are dermal denticles, sharp scales that cover the skin of most shark species.  Rather than bone, sharks have cartilage, which is much lighter and more flexible. In addition, their livers produce squalene, a fatty oil that helps them remain afloat. Their pectoral fins allow them to quickly change direction, dive and swim upward.
 http://animals.mom.me/unique-adaptations-sharks-survive-7845.html

The answer is observations and interpreting.