In general, piranhas are considered predatory carnivorous creatures. However, many predatory species show changes in diet during their growth. When young, they eat zooplankton, insects’ larvae, and small crustaceans; at middle age, they eat smaller fish and fish fins; and in adulthood, they become predators or scavengers (eating dead meat). 

Although there are several species of piranhas that are omnivorous — eating plants, fruits and seeds, insects, crustaceans, worms, and small fish — none of the species include humans in their common diet (read here for a documented list of all known piranha attacks). An interesting feeding behavior includes two species of the genus Catoprion, which rip scales from other fishes (a specialized feeding behavior called lepidophagy). Others such as young members of the genus Serrasalmus specialize in eating fish fins (pterygophagy). And the red-bellied piranhas of the genus Pygocentrus are carnivorous, principally eating dead, wounded, or drowned animals as they hunt in packs or schools.

Over the years, piranhas have developed a terrifying reputation as violent killers — a characterization that Hollywood turned into a five-picture horror series. However, we've come to learn that this stereotype is far from accurate. Find out what else we've gotten wrong about piranhas in this article from Smithsonian Magazine. 

You can also read the following Spanish-language articles written by the educator, Antonio Machado-Allison:
-Las Pirañas de Venezuela: Mitos y Realidades
-Los Peces Caribes de Venezuela: Una Aproximación a Su Estudio Taxonómico