i'm a bptanist and piranha are not native here, so i can't realyl tell. also, this was photographerd i Budapest and Hungarian is quite a difficult language, but that is what i could read there. maybe they are falsely called piranhas in some languages, i've seen strange native names for many species.
depends on the species, you can tell by their teeth. (i'm biologist) anyways, piranhas were found in one of our rivers, someone must have set them free (people obviously don't think of consequences it has on Nature) - and it turned out they were herbivorous species - someone caught them fishing carp
Pacu (Portuguese pronunciation: [paˈku]) is a common name used to refer to several common species of omnivorous South American freshwater fish that are related to the piranha. Pacu and piranha don't have similar teeth, although the main difference is jaw alignment; piranha have pointed, razor-sharp teeth in a pronounced underbite, whereas pacu have squarer, straighter teeth like a human in a less severe underbite, or a slight overbite. Courtesy of Wikipedia.
i was referring to fish expert that works with me, to whom images of piranhas found here were sent. he consulted experts worldwide to be able to tell for sure what they have found, were the fish dangerous for people and could they survive. they call them all piranhas at least in my language