information:classification, structural:reformatting, structural:expansion
Bioelectricity

The electric rays have specialised electric organs. Many species of rays and skates outside the family have electric organs in the tail; however, the electric ray has two large kidney-shaped electric organs on each side of its head, where current passes from the lower to the upper surface of the body. The nerves that signal the organ to discharge branch repeatedly, then attach to the lower side of each plaque in the batteries. These are composed of hexagonal columns, closely packed in a honeycomb formation. Each column consists of 500 to more than 1000 plaques of modified striated muscle, adapted from the branchial (gill arch) muscles. In marine fish, these batteries are connected as a parallel circuit, whereas freshwater batteries are arranged in series. This allows freshwater rays to transmit discharges of higher voltage, as freshwater cannot conduct electricity as well as saltwater. With such a battery, an electric ray may electrocute larger prey with a voltage of between 8 volts in some narcinids to 220 volts in Torpedo nobiliana, the Atlantic torpedo.