i have been bitten buy an oscar once, when i was cleaning the tank and he grabbed a finger(i guess it looked like food too him), got bit once by a male jack dempsey that was garding its babys( stupidity on my part from leaving my hand in the tnak and turning my head too see who scored in a hockey game), iv been bitten by convict cichlids a few time all times where when they where guarding there eggs or babys, and shocked by my electric catfish once will feeding. and lots of little bite from putting my finger on the surface of the water too see if the little fish like bettas and tetras would think its food.