- Other names: Gums, mysterious beast
- Country reported: Paraguay
The manguruyú was a cryptid reported to exist in the freshwater rivers of Paraguay by English explorer Percy Fawcett. He wrote that the Rio Paraguay was home to "a freshwater shark, huge but toothless, said to attack men and swallow them if it gets a chance".
As the only sharks which venture into freshwater, such as bull sharks, are certainly not toothless, British cryptozoologist Mike Grayson suggested the animal may have been a very large sturgeon, although he admitted that sturgeons do not attack people and are not found in South America. Karl Shuker opined that it may have been a giant catfish, either an old or freakish individual or a new species. German cryptozoologist Markus Bühler noted that the South American piraiba is large and deceptively shark-like.