An organ occurring on the body or tail of certain fish, such as the electric ray (Torpedo) and electric eel (Electrophorus electricus). It gives an electric shock when touched and is used either to stun prey or predators or, in some species, to maintain a weak electric field in the surrounding water that is used in navigation. The organ is composed of modified muscle cells (electroplate or electroplax cells), nervous stimulation of which greatly increases the potential difference across the cell. The electroplates are in series so a high overall voltage can be achieved.