The biggest fish alive filters plankton like a swimming sieve
Rhincodon typus, a slow carpet shark, is the largest living fish—one measured 18.8 m. Tropical oceans above about 21 °C are home; lifespan estimates run roughly 80–130 years. In April 1828 a 4.6 m animal harpooned in Table Bay, South Africa, let Andrew Smith name the species.
Rhincodon typus is the sole living member of its genus and family, a slow carpet shark and by far the biggest animal that is not a whale. Its name reflects bulk, not kinship: it is a fish, only distantly related to cetaceans. Science met it in April 1828, when a 4.6 m animal was harpooned in Table Bay, South Africa, and Andrew Smith, a doctor with British troops at Cape Town, described it the following year. Fossil teeth date back to the Late Oligocene of South Carolina.
It feeds from a mouth set at the front of a broad, flat head; one 12.1 m shark had a gape 1.55 m across. Twenty filter pads strain plankton, krill, fish eggs and sardines from more than 6,000 litres of water an hour, while over 300 rows of tiny teeth play little part. Skin up to 15 cm thick is patterned with pale spots unique to each animal, and even the eyeballs carry protective denticles and can be pulled deep into their sockets. A 2017 genome revealed an unusual rhodopsin tuned to blue light, which the shark switches off in warm shallows and reactivates in cold water around 2,000 m down.
Size remains slippery. An Arabian Sea female estimated at 18.8 m in 2001 is considered the most reliable record, and a 2015 review singled her out, while older tales, such as a shark impaled on the ship Maunganui in 1934 at about 17 m, are hard to verify. A decade of Ningaloo Reef data suggests males average 8 to 9 m and females grow larger. Lifespans are estimated at 80 to 130 years.
Whale sharks roam tropical seas mostly above 21 °C, gathering predictably off Ningaloo, Mexico's Yucatan and India's Gujarat and Kerala coasts. Tags show them diving as deep as 1,928 m. About three quarters of the population lives in the Indo-Pacific. Docile toward people, the species is listed as Endangered after declines of over 50% in 75 years from fishing, bycatch and ship strikes.
Source: Whale shark
