Watch an electric eel unleash a high-voltage strike on its prey

In the rivers of the Amazon rainforest is a fish like no other, a fish that you would not want to find yourself waiting 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 the 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're 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 one amp. The average shock from an electric eel lasts about 2 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, it could lead to drowning. And not only can the eel use electricity to stun or kill its prey, it can 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, but luckily for the electric eels, they can breathe air thanks to a special mucus 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 kilograms. 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 3 pairs of electric organs that run through the back portion of its body, the sax organ, the hunter 's organ and the main organ. The main and hunter 's organs are the high voltage producers used for defense and for stunning prey. The sax 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. 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 only on 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, and voila, a dipole has been created and the eel can start zapping. The electric charge flows towards the eel 's head 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 muscles and nerve cells already do. All muscle and nerve cells have electrical potential, and a simple contraction of a muscle cell 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 a lot 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 discs 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 salt water 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 Electro locate. 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 its electrocytes. Electric eels can even communicate using low voltage electric pulses. By varying 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'll 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 6:00, 100 volts or more. These attacks often cause the maximum possible muscle contraction, causing the animal to completely seize up. This is similar to how a Taser works. Then, once it's immobilized, the eel can feast. Electric eels don't have upper teeth, so they rely on suction to pull the prey into their mouth before swallowing them whole. For a long time, scientists thought that eels implemented these 2 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 started to notice 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, 2 high voltage pulses with an interval of about 2 milliseconds are emitted. After these 2 high voltage pulses, the eel takes a pause and then proceeds with its usual high voltage, high frequency attack volley. These 2 high voltage pulses are known as doublets and at first their purpose wasn't fully understood. Why let out 2 quick pulses initially if the massive attack volley will be more than enough to immobilize prey? Scientists carefully observed the eel 's behavior and noticed a few things. 1A 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 an 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 towards 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. 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 traveling 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. 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 hundreds of eels would then start to swim in circles, hurting the fish into prey balls and pushing them to shallower water. Then between 2 and 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 5 to 7 times, and each time a different subset of eels would produce the electrical attack. Although researchers weren't able to measure the voltage of the coordinated electric attacks, they estimate that 10 voltas 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 group 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 eels 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 with 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 shocks. 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're 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 us for a second but not kill us, to an eel, getting shocked is likely just a 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. It's 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. 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