Fun Fact of the Day 7/19

Well, due once again to my proximity a lake, I'll share another freshwater fun fact with you all this evening. I was playing "Crush The Castle 2" earlier today, and later on in the fantastic flash adventure that comprises that game, one of the fling-able weapons given to the player by a wizard is a jar of electric eels, used to elctrocute targets inside the castle walls via metal parts of the structure. As morbidly joyous of an experience as shocking enemies until they explode into little crimson showers was, the biologist inside of me did detect an error: electric eels can't generate anywhere near that much electricity. So that got me thinking: I should inform my readership about these animals for my fun fact today. And here I am.

Electric eels, despite their misleading name, are actually not eels at all. Actual eels belong to the order Anguilliformes, and this order includes such well-known species as the moray eel, and the enormous Atlantic conger eels. Electric eels, however, are closer related to catfish and carp than to true eels. Specifically, they belong to the family Gymnotidae, or the naked-backed knifefish. Unlike many true eels, the electric eel instead dwells in the freshwater of the Amazon river, like many of it's knifefish kin. Unusually for a fish, this animal also breathes air, rising to the surface every ten minutes or so to "gulp" it, obtaining 80% of it's required oxygen in this manner. They live in still or even stagnant water, feeding on invertebrates and small fish. They also have really quite interesting breeding manners as well. During the dry season, a male electric eel will make an actual nest out of his saliva, and the female will deposit a large number of eggs into it.

Now, all these things aside, the aspect that draws many people to electric eels is their namesake: their ability to generate electricity, known as bioelectrogenesis. Such a concept may inspire some pretty far-fetched images. But, sadly (SyFy, I'm talking to you.) images of electric eels setting whole stretches of water aglow with bright bolts of sizzling electricity, shocking all in sight with steaming glory are, perhaps obviously, defunct. But nonetheless, electric eels are impressive examples of the ability to do this. Now, overall, electricity did not evolve as a weapon. Knifefish, as a group use electricity not to attack or defend, but to navigate. Minute electrical fields on either side of the animal detect interruptions, allowing it to detect the direction of prey and orient itself even in pitch black conditions. And, to some degree, the electric eel can use it's shocking ability to do this as well. There are three portions of the eel's body devoted to electrical impulse production: the main organ, the hunter's organ, and the sachs organ. All three of these areas are located in the eel's tail, which makes up around 80% of it's body in the anterior portion. All three organs are comprised on a cellular level by specialized electrical cells called electrocytes. Electrocytes are flat, disc-shaped cells, with a positive charge on one side and a negative charge on the other. On their surface, they have acetylcholine receptors. When an electrical impulse begins, it originates in the so-called "pacemaker organ", a bundle of nerve cells that controls the rate of electrical impulses by sending and receiving them. When the electric eel detects prey, or a threat, this organ sends an impulse to the electrocytes, which are stacked like the inside of a battery to produce a current. When the nerves fire, they release ACH (acetylcholine), which binds to the ACH receptors on the cell surface. This in turn causes ATP powered protein pumps to actively transport large amounts of potassium and sodium ions out of the cell, creating an electric charge. Since the cells are stacked together, each one produces a charge of about 0.15 volts, but in current form, the organs can produce larger volts. The organs can produce both low and high voltage impulses, both of which vary in intensity based on the size of the eel. High voltage impulses from large adult eels can reach voltages of up to 650 volts, and 1 ampere of energy, which is potentially enough to kill an adult human. They use these impulses to locate food, to communicate, to hunt, and to defend themselves against predators.

Fascinating, isn't it? I love biology...