I've been nipped by some fish, but nothing serious, no blood.
My mom, however, has been bitten by the Pacu TWICE! First time she didn't believe me when I told her it had teeth, and she stuck her finger in there and it took a little tiny chunk of skin off! Second time was today when she was dangling shrimp in there and wouldn't let go. The Pacu bit half of the shrimp off and swam away, then came back for the other half, which my mom wouldn't release, so she engulfed the shrimp and part of my mom's finger. Her teeth cracked my mom's fingernail in two places from the middle of the nail down to the end.