Thanks a million, Discovery Channel. Now when you Google "largest shark in the world," six items on the first page of search results are derived from your ridiculous Megalodon "documentary" from last year. You know what? We don't need you to learn, and with the way things are going we're not likely to, anyway.
The real "largest [extant] shark in the world" is the Whale Shark, which is also the largest fish and non-cetacean in the world. Rhincodon typus is the only living member of the genus Rhincodon and the family Rhincodontidae, and emerged as a species some 60 million years ago. The reason that the Discovery Channel focused on the extinct Megalodon instead of this massive fish is likely because Whale Sharks are filter feeders, and it was probably beyond even the powers of selective editing to make these gentle giants seem like imminent threats to humanity. They are pelagic in nature, which means that they keep to the open ocean but don't spend time near the sea floor or the coasts. They eat krill, plankton, microalgae, the larvae of crustaceans and other small ocean life, like squid and fish. They are found in equatorial waters, between 30 or 40 degrees latitude.
There is no "bigger fish" story when it comes to Whale Sharks. The largest recorded Whale Shark measured 41.5 feet (12.65 meters) and weighed over 47,000 pounds (21.5 metric tons). Their mouths can be almost 5 feet (1.5 meters) wide. There are many more unverified reports of even larger individuals. They aren't usually seen in groups except for special occasions, when they gather in anticipation of the availability of huge amounts of food, due to the reproductive cycles of their prey. More than 400 Whale Sharks were observed off the Yucatan Coast in 2011, one of the largest gatherings ever recorded. Whale Sharks have incredibly thick skin, up to 3.9 inches (10 cm), and they have a pattern of pale yellow spots all over their backs. The patterns are unique to each individual, and are the primary characteristic researchers use to identify specific animals. Citizen scientists can help track the movements of Whale Sharks by contributing photos to this world database.
Whale Sharks are incredibly docile toward human divers, paying them little attention as they go about their business. Some divers have even been able to catch hold of the dorsal fin to hitch a ride, but direct contact with these animals is strongly discouraged - not for our safety, but for theirs. They are a major tourist attraction in areas they can be relied upon to frequent, but are best observed in their natural environment, as they do not do well in captivity. The mating habits and reproductive cycle of Whale Sharks is currently very mysterious, as it has never been known to be observed. But in 1996, a pregnant female was captured and was discovered to be holding 300 eggs in her body, proving that Whale Sharks are ovoviviparous, meaning that they lay eggs but incubate them internally. It is thought that the eggs do not hatch all at once, but that the female holds the male's sperm from her last mating and fertilizes her own eggs over a long period of time.
Whale Sharks are long-lived, having a lifespan of about 70 to 100 years, and reaching sexual maturity at 30 years. They are considered to be vulnerable by the IUCN, and several coastal countries where Whale Sharks have been known to gather have banned any commercial fishing, trapping, selling, import/export of any Whale Sharks, like Taiwan, the Philippines, and India. However, they continue to be hunted in other parts, and are poached in Taiwan and the Philippines. They, too, are hunted as the main ingredient in shark fin soup, and their parts can be sold for large amounts of money.