The whale shark, Rhincodon typus, is a slow filter feeding shark that is the largest living fish species. It can grow up to 12.2 m. (40 ft.) in length and can weigh up to 13.6 tonnes (15 short tons). This distinctively-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which is grouped into the subclass Elasmobranchii in the class Chondrichthyes. The shark is found in tropical and warm oceans and lives in the open sea and can live for about 70 years. The species is believed to have originated about 60 million years ago.
The whale shark is not an efficient swimmer since the entire body is used for swimming, which is unusual for fish and contributes to an average speed of only around . The largest specimen regarded as accurately recorded was caught on November 11, 1947, near the island of Baba, not far from Karachi, Pakistan. It was long, weighed more than 21.5 tonnes (47,300 lb), and had a girth of . Stories exist of vastly larger specimens — quoted lengths of are not uncommon in the popular shark literature — but no scientific records exist to support their existence. In 1868 the Irish natural scientist Edward Perceval Wright spent time in the Seychelles, during which he managed to obtain several small whale shark specimens, but claimed to have observed specimens in excess of , and tells of reports of specimens surpassing .
In a 1925 publication, Hugh M. Smith describes a huge whale shark caught in a bamboo fish trap in Thailand in 1919. The shark was too heavy to pull ashore, but Smith estimated that the shark was at least long, and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to a more precise measurement of and weight 43 tonnes in recent years. A shark caught in 1994 near Tainan County in Southern Taiwan is reported to have weighed 35.8 tonnes (78,887 lb). There have even been claims of whale sharks of up to . In 1934 a ship named the Maurguani came across a whale shark in the Southern Pacific Ocean, rammed it, and the shark consequently became stuck on the prow of the ship, supposedly with on one side and on the other. No reliable documentation exists of those claims and they remain little more than "fish-stories".
The whale shark is a filter feeder — one of only three known filter feeding shark species (along with the basking shark and the megamouth shark). It feeds on phytoplankton, macro-algae, plankton, krill and small nektonic life, such as small squid or vertebrates. The many rows of teeth play no role in feeding; in fact, they are reduced in size in the whale shark. Instead, the shark sucks in a mouthful of water, closes its mouth and expels the water through its gills. During the slight delay between closing the mouth and opening the gill flaps, plankton is trapped against the dermal denticles which line its gill plates and pharynx. This fine sieve-like apparatus, which is a unique modification of the gill rakers, prevents the passage of anything but fluid out through the gills (anything above 2 to 3 mm in diameter is trapped). Any material caught in the filter between the gill bars is swallowed. Whale sharks have been observed "coughing" and it is presumed that this is a method of clearing a build up of food particles in the gill rakers.
Whale sharks congregate at reefs off the Belizean Caribbean coast, supplementing their ordinary diet by feeding on the spawn of giant cubera snappers, which spawn in these waters between the full and new moons of March through September.
The whale shark is an active feeder, targeting concentrations of plankton or fish. It is able to ram filter feed or can gulp in a stationary position. The shark can circulate water at a rate up to 1.7 L/s (3.5 U.S. pint/s).. This is in contrast to the basking shark, which is a passive feeder and does not pump water; it relies on its swimming to force water over its gills.
This species, despite its enormous size, does not pose any significant danger to humans. It is a frequently cited example when educating the public about the popular misconceptions of all sharks as "man-eaters". They are actually quite gentle and can be playful with divers. There are unconfirmed reports of sharks lying still, upside down on the surface to allow divers to scrape parasites and other organisms from their bellies. Divers and snorkelers can swim with this giant fish without any risk apart from unintentionally being struck by the shark's large tail fin.
The shark is often seen by divers in many places, e.g. The Bay Islands in Honduras, Thailand, the Philippines, the Maldives, the Red Sea, Western Australia (Ningaloo Reef, Christmas Island), Belize, Tofo Beach in Mozambique, Sodwana Bay (Greater St. Lucia Wetland Park) in South Africa, at the Galapagos Islands, Mexico, Seychelles, West Malaysian and in Puerto Rico.
A whale shark is featured as the main attraction of Osaka Aquarium Kaiyukan and as of 2005, three whale sharks are being studied in captivity at the Okinawa Churaumi Aquarium in Japan. Four whale sharks, two males, Taroko, and Yushan, and two females, Alice and Trixie, are held in the Georgia Aquarium, in Atlanta. Two male whale sharks, Ralph and Norton, died in captivity at the Georgia Aquarium on January 11, 2007 and June 13, 2007 respectively. The two males were added on June 3, 2006 in hopes that reproduction in whale sharks could be studied in captivity. All six whale sharks were imported from Taiwan, where whale sharks are dubbed tofu sharks because of the taste and texture of the flesh.