Today's question comes from Ever Curious Andy who asks:
How do electric eels generate a voltage and why do they not get shocked in the process?An interesting question, especially for anyone who has ever been on the receiving end of one of those shocks. From what I've read, they can be quite painful, possibly lethal. But first, a clarification. Electric Eels, or Electrophorus electricus, isn't actually an eel, it's an eel shaped fish. It is the strongest of the electricity producing fish which also include electric catfish and torpedo rays.
Electric eels use electricity for everything, navigation, communication, eating and powering their homes. Just kidding on that last one. The electric eel doesn't "breathe", using their gills to extract oxygen from the water, as other fish do. Instead the electric eel's mouth is used to extract oxygen by gulping air above the water's surface. As a result of this, having a spiny, moving fish in their mouth would most likely damage their mouths to the point where they could no longer breathe. In order for the electric eel to swallow their prey whole, they need to either a) come up behind it all stealthy like and swallow it quickly, or b) zap the hell out of it and swallow the incapacitated thing. Usually they choose the latter.
To accomplish this, the electric eel has a combination of three electrical organs which take up roughly 4/5 of their bodies. One of these organs is used to generate a low level electric field used for navigation and locating prey. The other two are used to generate the pulse used to incapacitate prey and keep their George Foreman grill hot and ready to make burgers.
The two other electrical organs consist of thousand of electrocytes. Each electrocyte acts as a small battery, capable of generating about .15 volts. These electrocytes are stacked in series, like the batteries in your flashlight, such that the positive end of the battery is at the head of the eel and the negative end is at the tail. Now, .15 volts might not seem like a lot, but when 4000 of them all fire at the same time, the resulting shock is on the order of 600 volts, which is more than enough to make for a very bad day for you or I.
Rather than rephrase exactly how these cells work to generate a charge, I'll quote here:
In order for the pulse to be effective the eel needs to discharge all of its electrocytes at the same time. This is accomplished as a result of a combination of longer neural connections to the electrocytes closer to the head and thinner neurons which slow down the neural activity. In other words, the signal from the eel's brain to the electrocytes closer to the head are slowed down so that they arrive at the same time as the signals going to the eel's tail. As a result, all cells fire at the same time and boom goes the dynamite.
At rest, the Na+K+ pump, concentration and electrical gradient keeps the inside of the electrocyte at a resting potential of .08 volt. When the electric eel electrolocates its prey, the brain sends a signal through the nervous system to the electric organs. Acetylcholine is dropped onto the electrocyte which binds to the corresponding receptor on the ion. This opens the ion channels of the cell, allowing Na+ to rush in. The cell then depolarizes, momentarily reversing the charge, and fires. - Melissa Engalls, Electric Eel
Now, why the eel doesn't end up a deep fried specimen as a result of this, no one seems to know. Some folks seem to think that the eel does get shocked, but that the eel's location relative to where the shock is in the water keeps it from getting too shocked. Other ideas are that the eel's thick, course skin insulates it from the shock. One source I read mentioned that an eel with severely damaged skin will eventually shock itself to death, however I couldn't find anything else to back this up, and the fact that eels will drown if they don't gulp air enough makes me wonder if this particular eel's demise can be attributed solely to a poorly defined skin care regiment.
I can say, that from an evolutionary standpoint, if the electric eel did shock itself every time it went to eat, it would have died out long before you or I emerged from the muck and started discussing it. From a survival of the fittest perspective, any species that incapacitates itself when it tries to eat ain't sticking around for dessert. Uncle Larry's post-Thanksgiving dinner unconsciousness doesn't count.
For those of you who are thinking that the electric eel would make a fantastic pet, look elsewhere. The electric eel will pretty much shock anything that comes near it, so should you ever need to handle Li'l Sparky, you may find large gaps in your memory that just happen to coincide with when you tried to clean the eel tank. Better you should stick to goldfish.
Melissa Ingalls - Electric Eel
University of Bristol - The Electric Eel, T. Riis-Johannessen
Who Zoo - The Electric Eel, LaTasha Cormier
Scientific American.com - Ask the Experts: Biology