The Surprising Power of an Electric Eel’s Shock

Dec 9, 2014

Kenneth C. Catania

By Carl Zimmer

For thousands of years, fishermen knew that certain fish could deliver a painful shock, even though they had no idea how it happened. Only in the late 1700s did naturalists contemplate a bizarre possibility: These fish might release jolts of electricity — the same mysterious substance as in lightning.

That possibility led an Italian physicist named Alessandro Volta in 1800 to build an artificial electric fish. He observed that electric stingrays had dense stacks of muscles, and he wondered if they allowed the animals to store electric charges. To mimic the muscles, he built a stack of metal disks, alternating between copper and zinc.

Volta found that his model could store a huge amount of electricity, which he could unleash as shocks and sparks. Today, much of society runs on updated versions of Volta’s artificial electric fish. We call them batteries.

Now a new study suggests that electric fish have anticipated other kinds of technology. The research, by Kenneth C. Catania, a biologist at Vanderbilt University, reveals a remarkable sophistication in the way electric eels deploy their shocks.

Dr. Catania, who published the study on Thursday in the journal Science, found that the eels use short shocks like a remote control on their victims, flushing their prey out of hiding. And then they can deliver longer shocks that paralyze their prey at a distance, in precisely the same way that a Taser stops a person cold.

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7 comments on “The Surprising Power of an Electric Eel’s Shock

  • 2
    Haymaker says:

    Yes Roedy, good point. Another interesting question is how/why it might have evolved. Many predators use electricity to locate their prey but what steps were taken for this mechanism to evolve from a means of detection into becoming a full blown killing apparatus? OK ‘half an eye’ is better than no eye at all for distinguishing light from dark but a ‘mild electric shock as opposed to no electric shock at all’ would probably be worse than useless.
    Over to you Prof. Dawkins….

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  • Haymaker Dec 10, 2014 at 4:01 am

    Yes Roedy, good point. Another interesting question is how/why it might have evolved. Many predators use electricity to locate their prey but what steps were taken for this mechanism to evolve from a means of detection into becoming a full blown killing apparatus?

    You have identified the evolutionary mechanism, Electric eels still use small electric charges to cause hidden prey to twitch and give away their position, so they can be detected.

    There is a similar situation with whales and sonar.
    Whales use sonic projection to “see” prey in the dark depths of the ocean, (and to navigate) but some use high intensity sonic bursts as a weapon to stun prey.

    The transition of gradually building up intensity over evolutionary time-scales, is easy to understand.

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  • A company in the UK recently demonstrated the use of electric field disturbance for presence detection of moving bags of electrolyte…people. Its simple but there needs to be an electric field in the first place. The bags of electrolyte “short out” the field and distort its shape in the environment. Changes in this shape can be sensed and a moving body detected. Movement though is essential for detection. It may be that sensor fields generated are detected and reacted to by the target fish with a learned sudden cessation of movement to “hide”, but which only confirms to the electric predator a tasty bag of electrolyte, rather than some drift related vegetable matter. Slightly higher sense field strengths may invoke an involuntary muscle twich as shocks are inclined to do when fairly mild. This can better pinpoint the position of the snack. Closing in and learning to give more shocks, close enough together can stack up the twitch response so as to make muscles in the target lock up, as described.

    The evolution of higher strengths merely increases the range of these mooted capabilities. The eel could increase field strength just to improve range range of detection and then discover, getting very close to its still/hiding target that a pulse can cause a twitch. Causing twitches at a greater distance would be evolved for, to force a more useful disclosure of the target. Etc. Then improved range for stunning would continue the process.

    Just a guess.

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  • I worked on a 30kW high audio frequency side scan sonar once for wide strip deep ocean floor mapping. The Admiralty for a while considered it as a possible offensive weapon against Soviet subs in policing operations. The Min. of Ag and Fish wondered if it could be used by the fishing industry. It could and was as ghastly as fishing with dynamite. I got out of there, before any of this and promised myself after finding this out only to use “my powers” for good…

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  • I was thinking it was a defensive system long before it ever became a controlled offensive tool. A byproduct of its nervous system as it tried to get away?

    @ Roedy

    A very common question asked by people who learn about the amazing
    powers of electric eels is “Why don’t electric eels shock themselves?”
    After all, they’re in the same water as their prey – and the current
    is being generated right inside them. Part of the answer to that
    question is that they probably do, in fact, shock themselves. Electric
    eels in the process of shocking have been observed to curl up and
    thrash a bit, just as if they were being shocked. But clearly, this
    shock, something they would experience repeatedly, doesn’t
    incapacitate them. One possibility is that the eels have evolved to be
    resistant to the pain and damage caused by shocking. They feel the
    shock, but it doesn’t bother them as much as it might bother other
    animals. It could also be that the eel is insulated from its own
    shocks. Of course, it can’t be completely insulated. If it is going to
    shock the water and its prey, it has to be electrically open to
    current going out and coming back. Remember, however, that all the
    eel’s vital organs are located very close to its head. It’s possible
    that the eel is electrically constructed so that it’s head and
    internal organs are mostly insulated and the current flows out from
    and back into the rest of the body. This combined with a tolerance to
    the effect of shocks might provide the answer.


    For the purposes of comparison, an eel’s body has roughly the same
    dimensions as an adult man’s arm. To cause an arm to spasm, 200
    milliamps of current must be flowing into it for 50 milliseconds. An
    eel generates much less energy than that because its current flows for
    only 2 milliseconds.

    I have been an electrician for 40 years and I can tell you, the shocks you get when you don’t expect them hurt more than the ones when you do. Its less of a shock to receive the shock, if you see what I mean. I have only been caught once where the shock was more than just a second. It went on for about eight to ten seconds and, thankfully, only through one hand. It burned my skin quite deeply but did not go through my heart to cause ventricular fibrillation. Still, 8 seconds in between worlds was the strangest experience.

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  • 7
    NearlyNakedApe says:

    That’s a good question. Size could be one of those adaptations. Eels can stun smaller fish but can’t really seriously harm bigger fish like tuna, sharks or rays. According to, electric eels can reach 6 feet in length and 45 pounds in weight. So evolving a large body is probably one of adaptations: they feel the shock but are not seriously harmed by it. Maybe they also develop some kind of physical tolerance to them.

    The fact that all their vital organs are close to their head could be another. Maybe their brain and organs are enclosed in some kind of insulating membrane? These fish are quite fascinating and certainly deserve more in depth study. I am convinced we have a lot of things to learn from them.

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