This is a payara, from the Orinoco river. They are called "vampire fish" because of their 4-6 inch long fangs. This guy looks pretty chewed up, so I'm betting they're not the nicest of fish...
Are they related to pirahna? They sound fierce! Glad this little guy isn't showing the fangs... that might be too scary for me. LOL :) Thanks for posting it, and sharing the detail.
He does look a bit chewed up doesn’t he? They must be a sizeable fish if their teeth are 4 – 6 inches long. You probably don’t want to put him in with the guppies :-) I havn’t seen one of these before, thanks for potsting it.