I used to pet our pacu all the time when we did massive daily gravel vacs and water changes in the overcrowded 55 gallon tank our rescued fish came in. The tank was so chock full of fish, there was no way not to touch the fish when gravel vacuuming. The pacu liked to come up and swim in place to be petted, and would even push each other out of the way for petting. After they were moved into the substrate-free 300 gallon tank, I had rare opportunity to put my hand in the tank. It is also inconvenient, as I now have to stand on stepladder to pet the fish. One day, in front of company, I got out the stepladder to pet the fish. Our pacu, Adonis, had been bullied by Leonardo, and was hanging out on one side of the tank. After petting Leonardo, I moved the stepladder to the other side of the tank to pet Adonis. I was wiggling my fingers in front of him, when Adonis decided to taste my middle finger. I was lucky he only got the side of my finger and didn't bite my finger off. It bled profusely. I've never got off a ladder as quickly as I did that afternoon. It was a very foolish thing I did, considering I was undergoing chemotherapy and had a very compromised immune system. I had to tell my oncologist what happened, and the incident is a permanent part of my medical records! It was an all around embarrassing experience!