Electric Eel

Image: Josh More

It's Electrophorus electricus, a sober and serious scientific name which means "OMG! It's ELECTRIC, you guys!"

The Electric Eel is certainly electric but despite being long, thin and woefully lacking in the fin department, they aren't really eels. Rather they belong to the order Gymnotiformes, the South American Knifefishes.

Knifefishes look a bit like a knife! Their long, narrow body tapers away at the end and they have no pelvic fins, dorsal fins or tail fin. They rely totally on an anal fin that extends along the underside of almost their entire body. This, I suppose, is the blade of the knife. Unfortunately it ripples and undulates as the fish swims, which makes it completely inappropriate for carefully cutting away the crust of your master's sandwich. However, it allows the fish to swim forward and back with equal confidence, perfect for repeatedly stabbing your master in the gut. You'll get away with it too, because no-one ever suspects the butler.

Image: opencage

Electric Eels are a lot chunkier than most other Knifefish, almost cylindrical, in fact. But that just befits their station as the biggest Knifefish of them all; they can reach as much as 2.5 metres (8 feet) long! Knifefish have also swapped their scales for a thick covering of mucus. That's... good... too. I'm sure.

With this size Electric Eels can make a meal of all sorts of crustaceans, fish and even birds, mammals and amphibians they come across in the Amazon and other rivers in north-eastern South America. The first problem comes with finding it. Electric Eels live in water so dark and murky even they don't seem to trust it! More than three quarters of their oxygen requirements are met by rising to the surface and gulping air.

Image: Dave Lonsdale
Dark and murky waters

Add to that their poor eyesight and nocturnal habits, and it's pretty clear that their vision has little to offer. Especially since those eyes are small enough to give the Electric Eel the look of a particularly brutish resident of Sesame Street.

Their ears are more useful! The knifefish order is within a superorder called Ostariophysi. Member of this group have a swim bladder divided into two parts, one of which is directly attached to the inner ear by tiny bones. It greatly improves their hearing but really... it's the electricity, the ol' lecky that steals the Electric Eel's heart. And most of their body, too...

Video: Vincent Liew

It's almost frightening how devoted to electricity the Electric Eel is. We humans are absolutely stuffed with supposedly "vital" organs. We're like a big bag of offal with legs to move it around and arms to clear up after it. Electric Eels are different. Just 20% of their body-length is taken up by those organs. Heart, stomach, the bit that pays the mortgage, the bit that sends Christmas cards to people it hasn't seen in 20 years... just twenty percent.

The rest, the other four fifths, from a bit behind the gills to the tip of the tail, is all for the production of electricity. It's called the work/life balance, and Electric Eels have it written all over them. I mean inside them.

Image: Wiki-Harfus

And if you took a close look at those electrical innards you'd find thousands and thousands of specialised, muscle-derived cells called electrocytes. They're all stacked on top of each other so that they work like something called a Marx generator. Each electrocyte is charged up to a low voltage of just 0.15 V, but their powers combine when they're set off in unison. The effect is... what, exactly?

Well, it depends! Electric Eels have three different electric organs: the main organ, the Hunter's organ and the Sach's organ. When an Electric Eel is seeking food in dark and dingy waters, the Sach's organ emits pulses of about 10 V. This produces an electric field that the Eel is able to detect, and the field is distorted by any nearby objects or delectable flesh bodies. So it is that the Electric Eel builds a picture of the world through a process known as electrolocation, a twist on the bat's echolocation.

Image: Brian Gratwicke

It's also the reason why Electric Eels swim with their body so rigidly straight. Any swish of the tail or undulation of the body would distort their own electric field almost before it's produced. So that one, mighty fin has to do all the work.

Once the sweet, sweet electric field distortion of something juicy comes over the water, the real fun starts.

Video: NatGeoWild

And then it's over. About as quickly as it began! The main organ and the Hunter's organ produce a pulse of electricity, usually about 350 V but sometimes as much as 650 V. That's enough to stun or kill anything the Electric Eel could want to eat, which is good because they don't have enough teeth to get a firm grip on struggling prey.

Video: Geezart1982

It's also enough to stun or at the very least deter any predator. It must be so humiliating for a big, bulky caiman to be reduced to a gibbering wreck by a fish! Of course they have to run away, they don't want the other caimans to see them cry.

But these nifty electric organs are good for more than just hunting and killing and eating. They also use their Sach's organ for communication, which probably amounts almost entirely to whispering sweet, electrically discharged nothings to the opposite sex in the romantic dinginess of dark, mud-bottomed rivers.

Remember how Electric Eels are covered in mucus? Well, they're not always like that. They start out covered in spit. Males use their own saliva to create a foamy nest into which the female lays up to 17,000 eggs. He defends them until they hatch.

Image: Biopix, N Sloth

It's pretty clear from the ridiculous number of eggs that newly hatched Electric Eels are truly minuscule. They're 15 mm long before their first electric organs start to develop and more than twice that before the stronger ones start to grow. They're ready to leave the nest once they're around 10 cm (0.4 in) long, hopefully by then their sparks should be bright enough to fend for themselves.

I have seen one reference to "fish-based house security systems", which is a truly remarkable and hilarious idea. There's also synergy with my own piranha-based intruder-disposal system. Electric Eels have already been used to light up Christmas trees but seriously, they look like retired gangsters. If they've truly gone legit they're gonna need something more than decorations to spend their time on. If not, they'll go right back to Sesame Street all over again. You mark my words.