Deep laterally compressed bodies are generally silvery or golden in color, with a short adipose fin, jaws with a single row of sharp tricuspid sheering teeth and no molars. Other characids look somewhat similar but can be distinguished primarily by the dentition. Pacus (Colossoma spp.), and silver dollars (Metynnis spp.) as well as Myleus spp. and Mylossoma spp. have molar-like teeth used for crushing food. In telling Piranhas from Metynnis and other silver dollars, the angle of the jaw is a pretty good characteristic for sorting them...forward jutting lower jaw that forms a V at the angle is a piranha, even upper and lower jaw profile that forms a U at the angle of the jaw is not a piranha.
Predatory, with their dentition they are able to bite pieces out of larger prey, as opposed to having to swallow their prey whole, as do most North American freshwater fishes. Often feed in schools and exhibit feeding-frenzy behavior.
Age and Growth
Most less than 2 pounds but up to 16 inches and 6 pounds.
Image Credit: FWC