Why do piranhas leave some fish alone?

Number 8: Some piranhas are vegetarians. ... A piranha with half of its lower jaw chompers missing isn't out of the ordinary. The jaw bone of a red-bellied piranha .... Like grizzly bears, wolves, sharks, and pretty much any large scary thing with teeth, piranhas will leave you alone if you leave them alone. read more

Normally they will leave other piranhas alone. If kept well fed some piranhas will not bother fish of equal size and temperment. They are generally kept in a species tank; in other words keep them with other piranhas (not overcrowded) and you are far less likely to have problems. read more

Despite their flesh-eating reputation, some piranhas are omnivorous, eating more seeds than meat, and some even subsist on plants alone. For example, in the Amazonian rapids of the Trombetas basin in Pará, Brazil, scientists discovered that Tometes camunani lives solely off of riverweeds. read more