Just Shocking!

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By Linda | March 29, 2008

I recently wrote a post called Science and the Urban Legend in which I debunked (among other things) the false belief that eel skin wallets demagnetize credit cards because of the residual electricity left over from the eels they are made from. As with many of the topics I discuss on Science Junkies, answering one question brought up an entirely new one. Exactly how does an electric eel manufacture electricity?

The electric eel, Electrophorus electricus, is not a true eel but rather a species of knifefish. It is capable of generating powerful electric shocks, which it uses for both hunting and self-defense. It can grow to a length of over 8 feet and weight in excess of 45 pounds. Electric eels are capable of producing a shock of up to 500 volts and 1 ampere of current (500 watts). This is sufficient to harm an adult human.

The electricity is produced within three abdominal pairs of organs; the main organ, the hunter’s organ, and the sachs’ organ. These organs are made of electrocytes lined up in series so that the current flows through them and produces an electrical charge. When the eel locates its prey, the brain sends a signal through the nervous system to the electric cells.

Each electrogenic cell carries a negative charge of a little less than 100 millivolts on its outside compared to its inside. When the command signal arrives, the nerve terminal releases a minute puff of acetylcholine, a neurotransmitter. This creates a transient path with low electrical resistance connecting the inside and the outside of one side of the cell. Thus, each cell behaves like a battery with the activated side carrying a negative charge and the opposite side a positive one.

Because the cells are oriented inside the electric organ like a series of batteries piled into a flashlight, the current generated by an activated cell “shocks” any inactive neighbor into action, setting off a chain reaction that runs its course in less than two milliseconds. This almost simutaneous activity creates a short-lived current flowing along the eel’s body.

The electric eel has a surprising amount of control over how it releases the electical energy it produces, using lower discharges for “hunting” and higher intensities for stunning prey, or defending itself.