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The electric currents produced by some species of fishes, such as the Numbfish and torpedo rays are generated in cells called electrocytes. When an electrocyte is stimulated, a movement of ions (electrically charged atoms) across the cell membrane results in an electric discharge.
The electrocytes of most 'electric fishes' are modified muscle cells. Electrocytes are usually arranged in columns within electric organs. This arrangement increases the electrical output, much like a row of batteries placed end to end.
The electric organs of the torpedo rays contain about 45 columns of around 700 electrocytes. Electrical discharges escape through the dorsal surface of the fish. This is because the dorsal surface of both the electric organ and the body have less resistance than the surrounding tissues.
Torpedo rays can generate an electrical potential of 20 to 50 volts. Reports exist of fishermen who have received severe electric shocks from handling this fish.
There are a number of families that contain 'electric fishes'. Examples include the naked-back knifefishes (gymnotids) of South America, the elephantfishes (mormyrids) of Africa and the South American mochokid catfishes. The South American knifefishes (electrophorids) can generate pulses of over 500 volts.
- Helfman, G.S., Collette, B.B. & D.E. Facey. 1997. The Diversity of Fishes. Blackwell Science. Pp. 528.