Sharks are the biggest living fish in the ocean.  They are all different sizes and live in all different waters.  Sharks are fish that their skeletons are made out of cartilage instead of bones.  They generally have streaming lined bodies, fins, and gills.  They live in salt waters in all oceans, from shallow waters near to the shore to the bottom of the sea.
Some sharks are found in fresh waters.  There are 360 different kinds and types of sharks.  The most common shark is the Spiny Dogfish.  The largest shark is Whale Shark and the smallest shark is the Dwarf Shark.  The most dangerous sharks are the Mako, OceantnicWhitetip, Tiger, and Hammerhead sharks.  Most sharks are harmless to people but any wild animal may attack you.
	Sharks cannot swim as fast as healthy ones can.  Some sharks live up to 75 years of age.  But it is still a mystery why most sharks have unknown life spans.  The earliest sharks that have lived were the Cladodants.  They lived 370 millions of years ago.  Sharks are closely related to the stingrays and other sharks.
Most shark  are dark gray or blue on their backs with a lighter color on there bellies.  The pattern is called "Counter Shading".  It helps them to hide the shark from its prey or predators.  Sharks can drown if there gills are not working right or if they got hurt badly.  The sharks don't make entity sound at all.  They have no vocal chords.  Most scientists think sharks can see some color out of there eyes.  They can also see in the dark because they have like a mirror-like layer in the back called a Tarentum.