REVISION OF THE PIRANHA GENUS PYGOCENTRUS (TELEOSTEI, CHARACIFORMES)

Relative to other serrasalmins, Pygocentrus is diagnosable by several features, including prepelvic serrae number, morphology of the gas bla dder and skull, and head width. There are three species in the genus: P. piraya, P. nattereri, and P. cariba. Pygocentrus piraya is diagnose d by presence of adipose fin rays; it is restricted to the Rio Sao Fra ncisco of Brazil. Pygocentrus nattereri is undiagnosed and highly vari able in pigmentation. Its included populations are found in tropical a nd subtropical South America, east of the Andes, including the Amazon basin, the Paraguay/Parana system, and the rivers of the Guianas and n ortheast Brazil. Pygocentrus cariba is diagnosed by presence of four s upraneurals and a dark, prominent humeral blotch; it ranges through th e Rio Orinoco and its tributaries in Colombia and Venezuela. A key to the species is provided. All extant types or members of type series ar e illustrated. Morphometric analyses found no significant shape differ ences among the species; body shape is extremely stable both ontogenet ically as well as within populations. In contrast, color pattern in bo th preserved specimens and in life is highly variable ontogenetically and within populations.