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Whale Shark Anonymous asked this question on 5/25/2002: Is there any scientific information available about this fish?

beainsc gave this response on 5/25/2002: The Whale Shark (Rhincodon typus) ========= He is the largest and possibly the oldest living fish. This wonderful docile fish has had little research performed in the attempt to understand its behavior, longevity, reproduction, and benefits, due to its solitude. Family Name : Rhincodontidae. Common Name :Whale Shark. Scientific Name : Rhincodon typus. Adult Size : Up to 30 to 40 feet (9-12m). Habitat : Open water interior and exterior of reef. Occurrence : Common. Food Source : Plankton. As its name suggests, the whale shark is enormous and can grow up to 50 feet (15m) in length. It is the largest fish on the earth today.Width of mouth nearly as great as the breadth of head. Coloration: dark grey to a reddish or greenish brown on back and sides, including the upper surface of the pectorals. The whale shark is spotted with roundish white or yellowish series of spots, smallest on the head where they are less frequent. Variable number of narrow white or yellowish transverse stripes. Belly and lower parts are a whitish or white yellow. A 480 in. (1,200 cm) whale shark weighed about 27,000 lb (12,500 kg). It can be found in waters along the equator ±30-40° latitude.The whale shark is said to prefer waters of surface temperature 21-26 degrees centigrade, in areas where there are upwellings of nutrient rich colder water. These conditions favour blooms of plankton on which the sharks feed. They are often seen with schools of pelagic fish, especially trevally (Jacks). The sharks are divided into eight Orders according to their anatomical make-up. Such features as the presence or absence of an anal fin, and the number of gill slits determines their classification. The whale shark fits into the order of Orectolobiformes which have 5 gill slits, an anal fin, 2 dorsal fins, no spines on the fins, and the mouth well in front of the eyes. The word literally means "extended tail lobes", and some of the species in the order have very long tails. The internal organs of the whale shark have rarely been examined by marine biologists, as most of the specimens that have come to scientific attention have rapidly putrefied. The shark is said to have a small gullet, and while it might be able to take large objects into its mouth it would be unable to swallow them. The liver of the shark is huge, and in a twelve metre shark the liver alone weighs 1 tonne, 9% of the total weight of the shark. Extracts of the liver of the whale shark are reported to have strong anti-tumour activity. The caudal fin is well bent up with a notch at the base above and a keel on each side of the caudal peduncle. There are two dorsal fins. The mouth is large and can reach up to five foot in width with many small and conical recurved teeth. The eye is small with no nictating membrane. The gill apparatus forms a sieve of innumerable minute meshes through witch water is forced when the mouth is closed. Plankton food is thus retained and swallowed. The head is strongly flattened above and there appears to be no distinct snout, the mouth being at the anterior margin of the head. There is a spiracle about as large as the eye, a short distance behind and above the eye. The teeth are similar in the two jaws, in about three hundred and ten rows, with ten to fifteen rows functional all along the dental band.The appearance is like a large rasp on each jaw - hence the name of the shark: Rhineodon, the original spelling, means "rasp-tooth". There are certain features of the whale shark that distinguish it from other sharks. The most obvious is the very broad head. Like other Orectolobiform sharks, it has a wide mouth which is right at the front of the head, rather than being slung underneath the head as in other species. The olfactory opening of the shark is just above the upper lip, hidden in a nasal groove. There is a small barbel on the inside of the groove, reminiscent of another carpetshark family, the Nurse sharks, Ginglymostomatidae. The eyes of the shark are small and located behind the angle of the jaw. The shark closes its eye by rotating it and sucking it back into its head. It has nothing in common with whales except for its size and the fact that it only eats minute plankton by scooping it up whilst its mouth is wide open. It normally feeds on or just below the surface. It has on occasion, been observed eating fish larvae, krill, squid and sardines.The whale shark feeds by filtering small planktonic organisms out of the water through its 5 gill slits which have fine gill rakers. The gill slits are relatively large, reflecting its method of feeding - only the basking shark has bigger gills. It is remarkable that the sharks are able to filter prey that are only one mm in diameter. When actively feeding the gills flare out as the shark pumps large volumes of water through the gills at speed. Traditionally the whale shark is described as a suction filter feeder. By suddenly opening its mouth it is able to draw a large amount of water inside, which is then expelled through the gill slits. In the normal process of respiration the whale shark rhythmically opens its mouth about 200mm. When feeding it is able to open it 2-3 times as wide. Sometimes the sharks feed passively, cruising along beneath the surface with mouth agape. At other times it feeds much more actively charging around on the surface as when attacking a swarm of Krill. Whale sharks are viviparous animals, that is they are born live and do not hatch from eggs after they leave the uteri. In Taiwan a pregnant whale shark was harpooned and she contained 300 embryos in her uteri. The pups that were free from the yolk sac were up to 64cm(25 inches). (Environmental Biology of Fishes 46:219-223 1996). It is believed that maturity is reached between twenty five and thirty years of age. This maturity age gives the conclusion that they may live well over one hundred years. The skin on the back of the whale shark is thicker and tougher than any species in the world. The outer layer is covered in overlapping dermal denticles, a veritable suit of armour. Each denticle is 0.5 mm wide, and 0.75mm long. The point of each denticle projects backwards along the body. Underneath is a layer of connective tissue that is up to 140mm thick. The belly of the shark is much softer and the thickness of the connective tissue here is only 2/3 of the thickness on the back of the shark. They are very docile and gentle and, when approached by snorkelers or divers are uninhabited by the visit. The whale shark is one of the surviving giants of the ocean that has remained a mystery to fisherman, divers, and scientists alike until very recently.It is not known how far whale sharks migrate.Recent studies have shown that whale sharks migration can take them hundreds and even thousands of miles. One report showed that a single whale shark, equipped with a satellite tag, traveled 14,000 miles in 40 months (Brent S. Stewart, Ph.D. & Hubbs-Sea World Research Institute). At one time it was suggested that they might undertake huge migrations, breeding in the Indian Ocean, and drifting south in the Mozambique current around Cape Horn into the Atlantic, where they might be carried across the Atlantic in the Southern equatorial Current, reaching the Caribbean. (Gudger, 1931). Captivity The most remarkable achievement among many at Okinawa Expo Aquarium is the successful collection and display of specimens of the world's largest shark, the whale shark. This feat has since been duplicated at the Ring of Fire Aquarium in Osaka, where in 1992, two specimens, a male and a female, both over 20 feet long, were on display. The Izumito Sea Paradise Aquarium first displayed a whale shark in 1934. Okinawa Expo Aquarium displayed their first specimen in 1980. The collecting technique used by the aquarium exploits the facility's seaside location. Aquarists from Expo tow a special large barge to the collecting area some miles offshore. The barge has sides and a bottom but is open at both ends. When a whale shark is sighted, the barge is submerged so that the tops of the sides barely crest the water's surface. Swimmers guide the whale shark into the barge, close the two ends, and very slowly tow the barge with the enclosed whale shark to the pier at Okinawa. A hammock like sling is placed beneath the shark. Both shark and sling are hoisted with a heavy-duty crane into a flatbed truck carrying a very large tank of water. The truck carefully but quickly transports the shark to the aquarium where it is lifted into the tank. The large exhibit tank at Expo where whale sharks and other species are housed is 88 feet long, 39 feet wide and 11 feet deep and holds 290,000 gallons of water. It has held at least four specimens of whale sharks, one at a time, over the past two decades. Whale sharks have done well in captivity. The main problem they present is their large size at initial collection. In the future, small whale sharks may be displayed in many aquariums once collectors discover where to find juvenile specimens. beainsc recommends buying a book with the title, author, or subject: 1) Whale Sharks (Sharks) John F. Prevost 2) Whale Sharks : The Giants of Ningaloo Reef

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