Electrical Production

Production of Electricity

In theory, production of an electrical current should be easy for animals. Electricity is simply a difference in electrical potential between the two ends (poles) of a circuit, and a potential can be generated by concentrating positive ions, such as sodium, calcium, or potassium, at one pole and negative ions, such as chloride, at the other pole. Nerve cells do exactly this in order to generate a resting potential, and a current is released when an action potential travels the length of the nerve. Muscle cells also have resting potentials and release an electrical impulse as part of the sequence leading to contraction; for example, a electocardiogram (EKG) measures the electrical potentials of the heart muscle.

Of course, the current generated by nerves and muscles is small; for a current to have an effect outside an animal a much larger electrical potential must be generated. Electrical organs are modified nerve or muscle cells (most often muscle cells) in which the ability to pump ions, store them, and maintain a potential difference is enhanced.

Still, the electrical potential of each modified cell is small. Large potentials are generated by connecting the cells in a series. Think of 1.5 volt batteries in a flashlight. Batteries can either be wired in series or in parallel. In general, electric organs are arranged in series, maximizing the current (voltage) produced by the circuit, rather than the power (amperes).

Series wiring, connecting the positive pole of one battery to the negative pole of the next, adds the voltages of each battery in the series. When flashlight batteries are placed end to end, they are in series, and the voltages of the two batteries adds to 3.0 volts. Electric eels may have up to 6000 electricity producing cells. Even though each cell produces only 130 millivolts, wired in series the current generated is over 700 volts.

Electrical production for communication, predation or defense is limited to aquatic organisms. Because air is a poor conductor of electricity, electrical discharges would have little use for a terrestrial organism.

Electrical fish come in strongly electric forms, which use their electricity primarily for predation and defense, and weakly electric forms, in which the electrical signals are used in communication and electrolocation (as an analog to echolocation using sound).

Strongly electric fish include the electric catfish, electric eel, and torpedo
Freshwater weakly electric fish are the mormyriforms from Africa and the gymnotoforms from the tropical Americas
Skates are marine weakly electric fish.

Dunlap K. D., Zakon H. H. 1998. Behavioral actions of androgens and androgen receptor expression in the electrocommunication system of an electric fish, Eigenmannia irescens. Hormones And Behavior 34: (1) 30-38

Hopkins C. D. 1999. Design features for electric communication Journal Of Experimental Biology 202: (10) 1217-1228