Are piranha fish edible and how can they be prepare and cooked?

Yes they are edible.

There are several varieties of piranhas, but most reside in South America. Some related fish are often mistaken for piranhas, such as the peaceful, non-dangerous pacu.

It is not uncommon for local people (and tourists) to swim among piranhas. The fact is, except during lean times, piranhas are no more dangerous than other comparably-sized fish.

While people may fear being eaten by piranhas, in reality the situation is reversed. Piranhas are often a delicious and popular food where they are found.

http://www.wikihow.com/Safely-Swim-with-Piranhas

OK ! ! Leonard has it right

you might remember their teeth are sharp

as I remember they have large scales (from TV not personal observation)

as I remember all fish are eatable except the puffer fish and only a truly experienced cook can cook them up without poisoning the guests

quite tasty, gill , gut and scale , salt and cover with plain flour and fry till golden ,