Serrasalmus is a genus of freshwater ray-finned fishes belonging to the family Serrasalmidae, which includes the pacus, piranhas and related fishes. They are collectively known as pirambebas; the "typical" piranhas like the piraya piranha are nowadays placed in Pygocentrus. Like all piranhas, Serrasalmus are native to South America.

These fish are predatory, have sharp teeth and generally have a rhomboid shape. In some, the shape is more ovoid, particularly in old specimens. Some Serrasalmus species can exceed 20 in or 510 mm (S. manueli and S. rhombeus, according to OPEFE), placing them among the largest Serrasalmidae.

Middle Miocene-aged fossil remains of Serrasalmus are known from the Pebas Formation of Peru.

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