William L. Fink
Relative to other serrasalmins, Pygocentrus is diagnosable by several features, including prepelvic serrae number, morphology of the gas bladder and skull, and head width. There are three species in the genus: P. piraya, P. nattereri, and P. cariba. P. piraya is diagnosed by presence of adipose fin rays; it is restricted to the Rio Sao Francisco of Brazil. P. nattereri is undiagnosed, and highly variable in pigmentation. Its included populations are found in tropical and subtropical South America, east of the Andes, including the Amazon basin, the Paraguay/Paran system, and the rivers of the Guianas and northeast Brazil. P. cariba is diagnosed by presence of four supraneurals and a dark, prominent humeral blotch; it ranges through the R¡o Orinoco and its tributaries in Colombia and Venezuela. A key to the species is provided. All extant types or members of type series are illustrated. Morphometric analyses found no significant shape differences among the species; body shape is extremely stable both ontogenetically as well as within populations. In contrast, color pattern in both preserved specimens and in life is highly variable ontogenetically and within populations.