Breaking Down Science, Step by Step

Imagine you're a fish swimming through the dark murky depths of a tropical river, dodging piranha, river dolphins and other terrifying predators. Suddenly, your muscles cramp, leaving you in agony, frozen, floating and afraid as teeth lunge at you from the deep.

A paper published in science unveils the creepy ways in which electric eels use their powers to hunt their prey, and to control them remotely.


How do Electric Eels make electricity ?

Electric Eels have evolved to harness electricity using specific organs which act like big organic batteries. That may seem amazing to you, but it's essentially just a souped up version of a process which is happening in your muscle cells right now .

When your muscles are at rest, they pump out ions, leaving them with a slight negative charge. When a neuron activates a muscle, it uses neurotransmitters, such as acetylcholine, to open up pores in the membrane. As a result, all of those positive ions to flood back into the cell. These ions causes the muscle cells to contract.

To propagate this signal across the whole length of the muscle cell, there are "voltage sensitive channels". They react the moment ions start flooding in. They respond to the electrical stimulus, allowing the whole length of the muscle cell to respond instantaneously. Since they respond to charge alone, they can also be triggered by electric shocks.


The important thing to take away from this is that in some ways , muscles store electrical potential like a battery. Electric Eels have developed cells, similar to muscles, whose sole function is to store electricity. Using this organ, an electric eel can discharge up to 600V.

Electric Eels use them in three pairs of organs to hunt its prey. This goes further than just stunning its prey.


How do Electric Eels use Electricity to hunt ?

Electric Eels send out low voltage pulses to sense their environment. When they detect prey, they can send out a high voltage strike, stunning their victim.

Using high speed cameras, a captive eels and an unknown number of fish, a researcher at Vanderbilt was able to look at exactly how this high voltage strike works.


The prey of the eel is immobilized for about 3-4 milliseconds after the eels first shock. It's not a huge time window, and if the eel is too slow, its prey will recover quickly and escape.

What happens to the prey's muscles in this 3-4 millisecond time period is both fascinating and creepy. The Eel's electrical discharge is a series of rapid pulses which act to stiffen the whole body of it's prey. Those pulses could be activating the muscles directly, or they could somehow be controlling the nerves.


Nerves activate muscles using a neurotransmitter. If we blocked out all the neurotransmitters, and the prey still stiffened, then the Eels are controlling the muscles directly, but if they didn't, it means that the Eels are controlling the nervous system.

There is a toxin known as curare, which blocks neurotransmitters, and when it was given to the fish, they stopped reacting to the eel's electric shocks. So it looks like the Eels are directly manipulating the nervous system of their prey. Which part of the nervous system ?


To work this out, researchers removed the spines from dead fish, eliminating the central nervous system, and dangled them in front of the Eel. The Eel made them twitch. Which means that the Eels shocks worked specifically on the motor neurons of their prey.

Oh, I haven't even gotten to the creepiest part. Allow me to tell you about doublets...


Doublets ? Those are the things you wear .. right ?

Not in this case. You see, there is a third type of pulse electric eels send out. These pulses are known as "Doublets". These are two very quick bursts of high voltage charge which the Eel sends out when it's seeking out hidden prey. They aren't strong enough to stun, so what are they for ?


Imagine that you are hiding from an electric eel in the muddy waters of the amazon. Perhaps you are hiding in the undergrowth. Your best option is to stay still, and hope the Eel doesn't see you. Just don't move a muscle.

This is when the Eel sends out a doublet. The doublet makes you do the last thing you would ever want to do in this situation. It makes you twitch. That one movement alerts the Eel to your location, allowing it to strike before you can get away.

This is why the Electric Eel is a creepy puppet master. It can take control of the motor neurons of its prey, and not only paralyze it, but control it's behavior to make it easier to catch.

Validity Report-4/5

There are no statistics at all in this paper. Which is understandable, because they only have four eels at their disposal. But the experiments themselves are pretty straightforward. It tells a neat story. It doesn't provide an in depth description of why the electric field only affects the motor neurons, but there will be other papers to delve deeper into those questions. Apart from that, it's an easy read, with lots of cute supplementary videos, including this moment of pathos when the Eel realizes it's never going to get the fish.


Reference: The shocking predatory strike of the electric eel, by Kenneth Catania, in Science 5 December 2014: 346 (6214), 1231-1234.

Image Credit: Electric eel (Electrophorus electricus). Taken at the New England Aquarium (Boston, MA, December 2006. Copyright © 2006 Steven G. Johnson and donated to Wikipedia under GFDL and CC-by-SA.)

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