The manguruyú, is an unknown freshwater shark-like fish, more commonly called “Gums”, a humorous nickname inspired by the 1975 Stephen Spielberg thriller Jaws. It is known only from a brief account by British geographer and explorer, Col. Percy Fawcett. In his account, he wrote of a strange 18 foot “shark” that lived in the Paraguay River, saying; “a freshwater shark, huge but toothless, said to attack men and swallow them if it gets a chance.” Some have speculated Charles W. T. Craig’s account of a massive slug-like snake or fish is the same animal as the manguruyú.
Some theorize that the manguruyú is a bull shark, which can live in freshwater and can be found surprisingly far inland, but none have been found in Paraguay, and they quite obviously have teeth. British cryptozoologist Mike Grayson suggested it could be an exaggerated account of a sturgeon, although none have been found in South America. Other identities put forward include unknown catfish (Paraiba), lungfish, or a fish completely unknown in the fossil record.
It is worth noting that the gilded catfish (Zungaro zungaro), is sometimes called the "manguruyu," though they reach 20 pounds at sexual maturity, not nearly enough to "swallow a man whole." Gilded catfish are also not known to inhabit Paraguay.