Sharks are versatile and keen-sensed fishes, many species of which are able to hunt and eat nearly all the larger marine animals inboth shallow and deep seas.
Sharks also reveal great diversity in behavior and size.
Sharks are chiefly marine fishes found in all seas and are especially abundant in tropical and subtropical waters. Many species migrate up rivers, however and one bull shark, reaches Lake Nicaragua in Central America. Sharks are best known as aggressive carnivores that even attack members of their own species, but two of the largest sharks - the basking shark and the whale shark are docile feeders on plankton, which they strain from the water with sievelike gill rakers. Most sharks are grey in color and have leathery skin covered with small, sharp, pointed placoid scales, which, unlike those of bony fish, do not enlarge during the animal's growth. Usually five gill slits lie behind the lead.