My true percs "nip" at my hand when I'm trying to hand feed my CBS. Bugs the heck outta me when they shred the piece of krill before the CBS picks it outta my fingers.
...As for the water comment... One time I was feeding my CBS and watching my clowns shred the krill when the CBS got my finger while I wasn't paying attention. Didn't hurt, but scared the crap outta me. I yanked my hand outta the water right into my lights/reflector. Burned my arm (minorly) cause I couldn't free my hand from the angle it hit right away.
My sisters 10" oscar bit my finger once. I was running the diatom one day (if you've ever had an oscar, you'd know why I was running it), and when I was fooling around getting it started up, it must've thought my fingertip looked like it's food pellet. (The thing was on pond food cause the large size cichlid pellets were way too small, required some extra water changes and lots of other various food frequently, but it worked)... It bit, and it stung. Felt like a little electric shock. Nothing too bad, but sure scared the heck outta me. We had to move the oscar later and give him to my coach cause he kept growing. I think he is about a foot long now. We bought him from the LFS about 8 years ago or so when he was about 1.5-2".