In the rivers of the Amazon
rainforest is a fish like no other. A fish that you would not want to find
yourself wading in the water with. A specimen of this fish was brought to
Philadelphia from South America in 1773. It was observed that: It had the extraordinary power of communicating
a painful sensation, like that of an electrical shock, to people who touched it, and
of killing its prey at a distance.” It was a fish so unusual, that it would go on
to change the course of science - and in fact, the course of modern society - forever. Electric eels are a genus of
freshwater fish from South America, famous for their ability to stun their prey by
generating electricity, “Eel” is a misnomer, as they are actually part of the knife fish family,
and are more closely related to catfish than eels. And though they aren’t the only electric fish in
the world, they are by far, the most powerful. Some individuals are able to deliver
shocks at up to 860 volts and 1 amp. The average shock from an electric eel
lasts about two thousandths of a second. A single shock likely wouldn’t
kill a person, but it could seriously stun one. If shocked,
your muscles would briefly contract, and then you’d feel numb. If you were in the water
and got shocked, this could lead to drowning. It's one of only a few animals that can
kill its prey at a distance. And not only can the eel use electricity to stun or
kill its prey - it can also use electricity to control its target remotely - the
electricity coursing through the prey’s body, making it act in a way detrimental to
itself, and beneficial for the eel. And as formidable a hunter as an electric eel is
on its own, recent studies have discovered that they are not the solitary predators researchers
always believed them to be. They are in fact, proficient and effective pack hunters,
ambushing schools of fish in terrifying unison. How is it possible for a fish to generate so much electricity? And what has modern
science learned from this improbable creature? Electric eels live in streams, floodplains, and
swamps of the Amazon and Orinoco river basins in South America. Such murky habitats can be
dangerously seasonal for a fish. During the dry season, water levels drop, and oxygen availability
can plummet. But luckily for the electric eels, they can breathe air, thanks to a special mucous
membrane in their mouth that can absorb oxygen. Electric eels are snake-like in
appearance, and they are pretty huge. They can grow up to 8 feet,
or 2.5 meters in length, and weigh as much as 44 pounds, or 20 kg. They
don’t have scales, and instead, have slimy, dark gray or brown skin on the top of their body
and a yellow-orange color on the bottom side. And 80% of the eel's body,
by length and by weight, is dedicated to one thing: generating
ridiculous amounts of electricity. The electric eel has three pairs
of electric organs that run through the back portion of the its body: the Sach’s
organ, the Hunter’s organ and the Main organ. The Main and Hunters' organs are the high voltage
producers, used for protection and stunning prey. The Sachs' organ is capable only of producing low voltage pulses - its purpose is mainly
electro communication and navigation. These organs contain hundreds of
thousands of modified muscle cells called electrocytes. These are flattened
disk-like cells that are stacked in about 70 columns on each side of the fish’s body.
Each column contains 5000–10 000 electrocytes. In their resting state, these
electrocytes maintain a negative charge as the cells constantly work to pump positively
charged sodium and potassium ions out. And each electrocyte is connected to the
nervous system - but on only one side. When the eel senses prey or a threat, it sends a
signal through the nerve endings causing an ion channel on the electrocyte to open. Extracellular
positive ions can then flow back into the cell. The side without the nerve connection continues
to pump the positive ions out of the cell. This gives the left side of the
cell a relatively positive charge, and the right side a relatively negative charge. Voila, a dipole has been created, and the eel
can start zappin’. The electric charge flows towards the eel’s head, which is the more
positively charged side of its body, and is then discharged through the water towards prey. And the more cells that are stacked and lined
up, the more electricity they can generate. Because incredibly, the eel is able to open all
of its membrane gates at exactly the same time, creating a huge jolt of electricity. This seems like an extreme ability, but it's
an ability based on what typical muscle and nerve cells already do. All muscle and
nerve cells have electrical potential and a simple contraction of a muscle
will release a small amount of voltage. The cells of an electric eel have
simply amplified that potential. An eel’s ability to make electricity is often
compared to a battery - and this comparison is no coincidence. The very first battery, invented
in 1800, was inspired by the electric eel. Italian physicist Alessandro Volta observed that
electric eels had stacks of cells that looked like a roll of coins. He figured if he could
mimic this arrangement, he too, might be able to generate electricity. He cut coin-shaped disks
from various “dissimilar metals” and stacked them, trying to find any combination of
them that would create electricity. Eventually, he tried copper and zinc disks,
and separated the stacked pairs with saltwater. And lo and behold - electricity started
flowing. This came to be known as the voltaic stack - and is considered to be
the first electric battery ever made. Before this discovery,
scientists barely understood static electricity. And the electric eel
was only beginning to reveal its mysteries. Scientists soon realized that eels don’t have a one-zap-fits-all policy. They instead
are able to use different charges for different things - some for sensing their
environment, some for communicating, some for stunning their prey, and even some
for controlling the movements of their prey. Electric eels can control
their electricity with finesse. In their dark and murky habitat, electric
eels can’t rely on eyesight for navigation. In fact, their eyesight is extremely poor. They instead use weak electric discharges,
around 10 volts, to electrolocate. This weak charge emanates from their body, and
the eel can detect distortions in the electric field from objects either conducting or
resisting their electricity. This weak electric discharge is created when the eel simply
activates only a subset of it’s electrocytes. Electric eels can even communicate
using low voltage electric pulses. By varing the frequency that they produce
these pulses, researchers believe that eels can convey information about their
sex and reproductive receptivity. And, of course, eels use
their electricity for hunting. Electric eels are mostly nocturnal. They will wait
for darkness, and then sneak up on their prey, and unleash a series of high
frequency, high voltage pulses. In this video, the red frames indicate
when the electric organs are discharging. After just a few milliseconds the
prey is completely immobilized. Such a high frequency, high voltage attack induces
massive whole-body muscle contractions in the prey fish. The electric shock causes the prey fish’s
motor neurons, and thus their muscles, to become simultaneously activated. The higher the voltage,
the more intense the muscle contraction - and at 600 volts or more, these attacks often cause
the the maximum possible muscle contraction, causing the animal to completely seize
up. This is similar to how a TASER works. Then, once it is immobilized, the eel can
feast. Electric eels don’t have upper teeth, so they rely so on suction to pull the prey
into their mouth before swallowing them whole. For a long time, scientists thought that eels
implemented these two types of discharge - low voltage for navigation and communication; high
voltage for immobilizing prey. But, they soon learned, there is more to the story. And that eels
use their electricity in even more cunning ways. When looking at the timing of the electric pulses,
researchers noticed an interesting pattern. ‘‘Introduction of prey into the aquarium
arouses the eel, causing it to swim around, but often stopping in a
particular corner of the aquarium. During these stops, two high-voltage pulses
with an interval of about 2 ms are emitted.’’ After these two high voltage
pulses, the eel takes a pause, and then proceeds with its usual
high-voltage, high frequency attack volley. These two high voltage pulses are
known as doublets - and at first, their purpose wasn’t fully understood.
Why let out two quick pulses initially, if the massive attack volley will be
more than enough to immobilize prey? Scientists carefully observed the eels’ behavior, and noticed a few things. 1) a massive attack
volley would almost always come after the doublet; and 2) the doublets themselves resulted in
a massive whole body twitch in nearby fish. Perhaps the purpose of these
doublets was not to stun the prey, but to force the prey to
reveal its location to the eel. To test this, scientists
set up a clever experiment. On one side of an agar barrier they placed an
electric eel. On the other side of the barrier, they placed a dead fish, and connected
it to a electrical stimulator. The fish was then sealed in a bag, and
electrically isolated from the eel. The scientists could electrically jolt the fish with their
stimulator, but the eel could not. The stimulator was set up so that when the eel emitted a doublet,
it would send a similar shock to the dead fish. When the eels emitted its doublet, and the dead fish received the simulated doublet -
the eels immediately responded to the twitch with a high-voltage volley
and strike toward the dead fish. But when the investigators
turned off the stimulator, and the eel emitted its doublet - no twitch was
produced in the dead fish, and the eel did not attack. The eel would only attack the fish if
it first twitched in response to its doublet. This study shows that electric eels
can indeed remotely control their prey, forcing them to reveal their location. The
doublet allows the eel to ask the question: any fish out there I can eat? The
prey have no choice but to respond. But what if an eel finds itself near an entire
shoal of fish - a shoal that seems particularly good at keeping its distance to avoid such
shocks? To deal with this, some electric eels display a remarkable behavior - a behavior
unprecedented in the world of electric fish. Social predation - where groups of
animals coordinate to hunt and kill prey - is a tactic commonly
seen in mammals like wolves, orcas, or lions. In fish, this
behavior is almost unheard of. So when scientists travelling through
the Amazon river noticed groups of eels, sometimes over 100 of them, seemingly
rounding up and attacking prey together, they almost could not believe their eyes. And
these weren’t just any of the electric eels - they were volta eels the most powerful of any of
the electric eels, with shocks up to 860 volts. At dawn and dusk, the scientists
noticed an increase in eel activity, with many individuals leaving the murky
depths and swimming near the surface, appearing to congregate. These groups of eels
would then swim together towards a shallow hunting area that contained thousands of small fish. These
groups of sometimes 100s of eels would then start to swim in circles, herding the fish into prey
balls, and pushing them to shallower water. Then, between 2 to 10 individual eels would
launch a joint predatory strike. In this video you can recognize the attacking eels by
their synchronized sinusoidal body posture. The fish hit with the electrical attack
spasm so hard that they jump out of the water - and then return to the surface stunned and
motionless. The eels then quickly eat the fish. The eels would carry out this
attack sequence five to seven times, and each time, a different subset of
eels would produce the electrical attack. Although the researchers weren’t able to measure
the voltage of the coordinated electric attacks, they estimate that 10 Volta’s electric eels
working together could create 8600 volts. This hunting technique allows the eels to subdue huge quantities of prey that would
normally be too evasive to capture. And it’s not just that these eels
were stuck together in a confined area, forcing them to feed
on the same groups of fish. These eels were congregating from far and
wide, to repeatedly forage together over time, using communication in the form of low
voltage electric pulses and body posturing. It’s unknown if the eels have any
familial relationship to each other, like is common with many other pack hunters.
But scientists are working to find that out. Only 9 other species of fish have ever been
observed to hunt together - and the electric eel’s tactics may be the most formidable. This
shows us that animals we think we understand can have more than one survival strategy - that in
isolated regions and specific groups of animals, predator prey interactions may
not be at all what we expect. One lingering question that may have come to your
mind is - how do the eels not shock each other? It’s believed that the electric organ
of an electric eel is padded with adipose tissue that insulates the
fish from its own electric shock. But how do they prevent getting
shocked from other eels? The likely answer is, that they don’t. Electric eels are probably pretty huge for exactly
this reason. They are much larger than their prey - such that an eel’s current will easily
incapacitate their target, but won’t do much to their larger bodies, similarly to how a single
electric eel shock to us would hurt for a sec, but not kill us. To an eel, getting shocked
is likely just part of doing business. An eel’s entire world revolves around its
electricity. And largely thanks to the electric eel, so does ours. Next time you charge your phone
or stick some double As in your remote, you can thank the electric eel for its contribution to our
understanding of electricity. And we continue to be inspired by them. Researchers are currently
working on an entirely new type of battery inspired by eels - a soft and flexible battery
that can power medical implants and soft robots. We are likely just beginning to
understand these incredible creatures, with many more of their mysteries still
lurking in the muddy waters of the Amazon. Understanding the electric eel has ignited
a curiosity in me about the electricity in the world all around us. Its nearly
impossible to NOT take it for granted. I know I certainly don’t often think
about how the lights in my kitchen work, how my computer stays charged, or how the
grid in Texas is teetering on a knife edge and is doomed to fail at any moment - ok maybe
I do think about that last one. But in general, how electricity works is rarely on my mind. But
the more I learn, the more incredible it becomes. With Brilliant’s Electricity and Magnetism
course, you can discover the physical laws of electricity and magnetism that are the backbone of
our modern world. It begins with simple analogies, and walks you through step by step how electricity
was discovered, and slowly building to explain some fundamental equations that look complicated,
but make total sense when every step is broken down for you. It’s not overwhelming like college
classes can be, and rather than penalize you when you get an answer wrong, it guides you to the
right one with a more in depth explanation. There are so many courses to dive into, from neural networks to algorithms,
to the physics of every day. To get started for free, visit to
brilliant.org/realscience or click on the link in the description, and the first 200 people will get
20% off Brilliant's annual premium subscription. And if you’re looking for
something else to watch right now, you can watch our previous video about the
mysteries of deep sea gigantism - or watch Real Engineering’s latest video
about self healing space suits.
They're at least A, if not S.
As long as they stay restricted to the water realm I'm fine with them.
Electric eels are easily S-tier. They have a broken sensory ability, hunt in both packs and as solitary critters, can punch way above their weight class if they have to.
But what moves them from high-A to low-S in my opinion is that they have two kinds of electrical pulses and are smart enough to use them in conjunction. The first stuns prey. The second one causes involuntarily muscle contractions. So even hiding in the soil or the surroundings doesn't work against a determined electric eel, they can just force you out of your hiding spot.
Tried out a knife fish build once and it’s not for me, but mad respect to the mad lads who turn a sensory upgrade into a deadly aoe