We spent many hours a week vacuuming out the 55 gallon tank our rescued fish came in. It was so crowded, the fish became used to our hands in their tank. Our pacu would literally swim in place for petting. They are very dog-like in behavior and would actually push each other out of the way to receive maximum attention. Since we don't vacuum their current tank, in the last year the pacu have forgotten how they loved to be petted, and have grown a little shy. I'm a little shy about petting them, too. About a year ago, I was showing off and petting them. I have to stand on a step ladder to get my hand in our 300 gallon tank. One of the pacu had been bullied and badgered by the other one, so was staying on one side of the tank out of the other's way. I moved the step ladder to the far side of the tank to pet Adonis in front of my audience and was waggling my fingers in front of his face when he decided to taste my middle finger. It was quite embarrassing, and since I was undergoing chemotherapy and had a very compromised immune system, it would have been really bad if the bite had become infected. It's in my oncology record that my fish bit me! I didn't stick my hand in the tank until my cancer treatment was over, and by that time the pacu had become shy to petting. BTW, they have extremely tough muscular bodies--they feel like hard tire rubber--they're not at all like the oscars who seem so light, delicate and fragile in comparison.