It’s been a stressful and exciting week in my household. We had a big rainstorm over the weekend, and our roof started leaking. Not great! But want to know what was even worse?
Water started coming out of our breaker box…yeah, not an ideal scenario!
It’s all fixed now, but it got come thinking – what animal does just fine mixing water and electricity?
The electric eel!
The word ‘eel’ is actually a bit of a misnomer. Electric eels (genus Electrophorus) are knifefishes – long, blade-shaped fishes that swim by rippling a long anal fin on their belly. Unlike true eels, which typically live in saltwater, knifefishes generally are freshwater creatures.
There are three species of electric eels, all of which live in the Amazon River. The discovery of three species is actually a recent one. Until 2019, scientists thought there was only one species of electric eels. DNA evidence divided electric eels into three species: Electrophorus voltai, E. Varii, and E. electricus. Each species lives in slightly different regions of the Amazon and looks slightly different. But all of them can get quite large, getting up to eight feet long and weighing 44 pounds.
The electric source
Electric eels make electricity from three electric organs – a main organ, a Hunter’s organ, and a Sach’s organ. The main organ and the Hunter’s organ are the heavy hitters, creating high-voltage electricity to stun prey and scare off predators. The Sach’s organ produces a much lower voltage for communication and navigation. These organs take up most of an electric eel’s body: 80% of an electric eel’s body is electric organ. Vital organs (brain, heart, etc.) take up the other 20% right behind their head.
The actual electricity comes from special disc-shaped electricity-producing cells called electrocytes. Electric eels have about 6,000 electrocytes in their body, each functioning as a tiny battery. When the electric eels want to make a shock, a signal is sent from the nervous system to these electrocytes. This signal makes positively-charged sodium ions flood into the cells, creating a potential gradient. To get the cell back to equilibrium, more sodium ions leave the cell, and electricity is discharged. This is the same way that our brains work – changes in the concentration of ions in our brain cells create discharges of electricity that make cells fire (How Stuff Works can explain it better than me here).
Electric eels can create much larger amounts of electricity than our brains can because of how their electrocytes are oriented. Electrocytes are stacked tightly in columns. When one electrocyte goes off, it sets off the others around it. This creates a cascade of current, with the 50 millivolts of electricity from one electrocyte quickly growing into a discharge of up to 860 volts.
But why?
So that’s the nuts and bolts of how electric eels make electricity, but why do they do it? Electric eels use electricity for multiple tasks, including hunting, echolocation, and communication.The strongest electric pulses are used for stunning prey. Some hypothesize that electric eels evolved to use electricity for hunting to protect their delicate mouths. Electric eels don’t have teeth in their upper jaw; instead of chomping on their prey, they must vacuum them up with their mouths. You’re a lot less likely to get your mouth hurt by a struggling fish if you stun it first!
Electricity also has other hunting uses, like stunning prey to keep them from escaping or making them reveal themselves with a twitch. Electric eels also have a good strategy for larger prey. By curling themselves around the body of a large fish, electric eels can double the strength of their electric field. Then, they deliver a series of shocks to make the prey’s muscles contract repeatedly until fatigue sets in.
Electric eels also use their electricity to ‘see’ their surroundings. On top of their poor eyesight, electric eels are nocturnal and live in muddy water. So to find anything, they use weak electric discharges to echolocate and identify foreign objects. Electric eels do so by detecting when there’s a disturbance in the electric field around them.
Finally, electricity plays an essential role in electric eel communication. Electric eels use weak pulses to convey information about themselves, with the frequency of these pulses varying between sexes and across individuals. Electric eels can even share information about their sexual receptivity, which is super important during the breeding season.
Don’t they shock themselves??
Usually not!
Electric eels have thick skin, which helps insulate them from their own attacks. They also have layers of fat around their electric organs that serve as insulation to protect the rest of the body. Plus, their brain is at the opposite end of the body from their electric organs, which helps keep them safe.
However, if there’s a breach in their skin (i.e., a wound or scratch), they can definitely shock themselves. The risk for self-stunning also increases when electric eels are out of the water, potentially because their wet skin acts as a solid conductor.
Other weirdness
Beyond the whole electricity thing, electric eels have a lot of interesting quirks.
For instance, it was discovered relatively recently that electric eels are not always as solitary as we thought. One species, Volta’s electric eels, will sometimes hunt in groups. A group of Volta’s electric eels can successfully ambush an entire school of fish by coordinating their movements and the strength of their shocks.
Sometimes, electric eels need to defend themselves against predators. But their electric charges dissipate and are not as strong when in all that water. So, if they want to make a point, electric eels will jump out of the water and directly onto a predator to deliver a maximal shock.
Electric eels also breathe air and come up for a breath about every 10 minutes. Their mouths are filled with blood vessels, so electric eels use their mouths as lungs. While they do have gills, their gills are only used to get rid of carbon dioxide and don’t take in any oxygen.
Are they dangerous?
I mean, yes and no. I think that you should always treat wild animals with respect. Just because an animal hasn’t bitten/stung/attacked yet doesn’t mean it can’t. So you should never get up in a wild animal’s space unless you are trained or have a trained professional with you.
Okay, soapbox over!
To the more specific question of are electric eels dangerous: I mean, they can shock you! And while 600 volts probably won’t kill you, it will hurt and be unpleasant! Plus, multiple shocks could cause respiratory or heart failure. And if you do get stunned, you could fall and drown in the shallow water where you ran into an electric eel.
So yeah. Be careful when wading in South American rivers. Electric eels won’t be hunting you, but they will release a shock if you disturb them!
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