Got nailed by a 10" wolf fish (Hoplias malabaricus)....almost needed stitches. The thing was sitting at the bottom of the tank, facing away from my hand (I was fixing a filter hose fitting) and wheeled around 180 degrees in about 1/4 of a second and grabbed my hand and shook its head like a shark. Completely tore my hand open. I just sat there for about 10 seconds, watching blood flow out of my hand, with a mixture of fright, awe, and fascination on my face! Needless to say, I didn't stick my hand in his tank again with him in it.