Sharks range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species that is only 17 centimetres (6.7in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40ft) in length. They are found in all seas and are common to depths up to 2,000 metres (6,600ft). They generally do not live in freshwater, although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.
The finetooth shark, Carcharhinus isodon, is a species of requiem shark, family Carcharhinidae, found in the western Atlantic Ocean from North Carolina to Brazil. It forms large schools in shallow, coastal waters and migrates seasonally following warm water. A relatively small, slender-bodied shark, the finetooth shark can be identified by its needle-like teeth, dark blue-gray dorsal coloration, and long gill slits. It attains a maximum length of 1.9 m (6.2 ft). The diet of this species consists primarily of small bony fishes, in particular menhaden. Like other members of its family, it is viviparous in reproduction; every other year, females give birth to 2–6 pups in estuarine nursery areas. The finetooth shark is important to the gillnet shark fishery operating off the southeastern United States; the meat is sold for human consumption. Its population has not yet been depleted, but the US National Marine Fisheries Service (NMFS) has determined that fishing is occurring at unsustainable levels.