An electric eel (Electrophorus electricus) has current-producing organs made up of electric plates (modified muscle cells) on both sides of its vertebral column running almost its entire body length. The charge—350 volts on average, but as great as 550 volts—is released by the central nervous system. The shock consists of four to eight separate charges, each of which lasts only two- to three-thousandths of a second. These shocks, used as a defense mechanism, can be repeated up to 150 times per hour without any visible fatigue to the eel. The most powerful electric eel, found in the rivers of Brazil, Colombia, Venezuela, and Peru, produces a shock of 400 to 650 volts.