Electric fishes


It’s hard to imagine modern life without the stuff. It heats, cools, and lights up our homes and businesses, reduces the chaos of transportation, and because it powers technologies that allow for communication across vast geographic areas, it is the lifeblood of the Information Age. Over time, we’ve discovered that the utility of electricity is ludicrously diverse; from keeping food cold enough to prolong preservation, to saving lives through defibrillation of the heart, to being a dick to your friends. The fact that I am currently writing this on a laptop computer, and then disseminating the information in it over the medium of the Internet, is an undeniable consequence of humankind’s harnessing of electrical energy.

If you are inclined to think of the control and use of electrical energy as a human “invention”, then prepare to set your anthropocentrism…and perhaps yarns telling of curious, bespectacled statesmen armed with kites and keys…aside. Humans are far behind the curve, by many millions of years, on this front once the rest of the animal kingdom is considered, because just like with light (which I’ve talked about before), many animals can produce their own electricity.The overwhelming majority of these animals are at least partially aquatic, since water is a far better conductor of electricity than air. Of these gifted organisms, the bulk of them are vertebrates, and in particular, among our finned and gilled friends, the fishes. There are some mammalian exceptions, including monotremes (the platypus and echidna) and perhaps a species of dolphin or two, but by and large, it’s fish that have locked down this electricity thing. Volta, Tesla, and Edison were great and all, but the reality is that animals not too distantly related to the flaky goodness in your Gorton’s fishsticks had them solidly beat by eons, evolving a commanding grasp of the power of electricity right into their bodies.

On a microscopic scale, there are electrical properties observable in essentially all animal, plant, and fungal cells, as there is an inherent voltage difference maintained between the surface of the cell membrane and the interior of the cell. This voltage condition stays stagnant in most cells, but in some animal cells, like nerve and muscle cells, the electrical membrane potential can quickly rise and fall (generating the release of an “action potential”; see: neurons in brain “firing”) through use of special gates in the membrane that pump charged atoms (ex., sodium ions) across the membrane in an incredibly fast cycle of increasing electrical potential, followed by sudden, temporary, dramatic reversal of membrane polarity. This process is critical to the response of these cells to external stimuli, the facilitation of intercellular communication, and, ultimately, the relay of information through cellular circuits. Your neural, muscular, and hormonal systems are made useful by the tightly orchestrated rhythm of many trillions of daily electrical impulses from innumerable, tiny, cellular batteries. Every thought, every heartbeat, every movement you’ve experienced has been instigated by the flashing of all-or-nothing action potential spikes. Your life, from the perspective of your excitable systems, is a bit like an 80 year long rave, faithfully illuminated by the regular pulsing of strobe lights…but with less MDMA and ketamine.

Cellular level mastery of electricity is nearly universal in the animal kingdom, however, and the capacity of the “electric fishes” to step it up to the scale of the whole organism is something special. This generally occurs in two forms: electroreception, which is more common and involves the ability to perceive natural electrical fields as a kind of “sixth sense”, and bioelectrogenesis, which is when the animal actually produces an electric field or discharge. Many electrogenic fish, which are the focus of this entry (because they are badass), are also electroreceptive, and can use their produced electrical ‘aura’ to enhance their perception of their environment, or even communicate with other members of the same species.

“Baby girl, turn me on with your electric feel…”

Perhaps the most obvious example of bioelectrogenesis in fish is the electric eel (Electrophorus electricus…no surprises there). It’s not technically a “true eel” (fishes in the order Anguilliformes), and is actually a knifefish (order Gymnotiformes), a group of slender,  freshwater fish found exclusively in South America that are related to catfish, carp, and minnows. All knifefish have the ability to produce an electrical field, but this power is excessively enhanced in good ol’ Electrophorus, which also happens to be the largest member of the Gymnotiformes, reaching the length of a couch.

Much of that impressive length is made up of the electric organs. These organs, common to all electric fish, are made up of evolutionarily-derived muscle or nerve cells, called electrocytes. Electrocytes are disc-shaped and stacked closely together (think Pringles chips layered in their container), so that each one adds to the total difference in electrical potential, somewhat like a voltaic pile, or the plates in the lead-acid battery that starts your car. The electrocytes, numbering in the many thousands, once stimulated by the neurological system, go through the same rapid, electrochemical switcheroo found in normal muscle or nerve cells, suddenly, almost simultaneously, reverse in polarity, and effectively generate an electric current that runs down the length of the organ and out into the surrounding water…all in a fraction of a second. In Electrophorus, the cumulative effect of all of these electrocytes discharging at once is extremely powerful…definitely strong enough to be used both for stunning prey (invertebrates and smaller fish), and for defense. If your butthole isn’t adequately puckered at the thought of that, note that adults can deliver a punch registering at upwards of 500 to 700 volts with a current of 1 ampere, which is enough of a shock to stop the heart of pretty much any animal on the planet sufficiently foolhardy enough to tangle with Electrophorus, something this predator found out the hard way. For some perspective, consider that if you could harness an entire Electrophorus discharge, you could power something like a hot plate or microwave. Or a decked out Christmas Tree.

So, electric eels, if sufficiently agitated by meddlesome humans, can potentially remedy the situation by replicating the exhilarating experience of shoving a knife in a household wall outlet, resulting in the perpetrator’s immediate demise. Death-by-eel is rare for humans, but it does happen, sometimes merely as a result of drowning after being blasted unconscious. Therefore, it’s advisable not to mess with Electrophorus, unless you think being found face down, floating in a swampy, Neotropical puddle, dispatched by a pockmarked fish that didn’t even touch you, seems like a dignified way to go.

Electrophorus may be the most famous, and dangerous, of the electric fish, but there are certainly many additional, possibly even stranger, species that receive little attention. And no, this guy isn’t among them.

A not-so-distant relative of the electric eel, found all the way across the Atlantic in tropical Africa and the Nile River, is the electric catfish (family Malapteruridae). Externally, malapterurids look like conventional catfish. Species range in size from about the length of your hand, up to the size of your leg. Many are dull brown in color, and sort of look like little smokies with eyes and tentacles.

Take THAT, appetite for breakfast tomorrow!

Its electric organ, derived from muscle tissue, lines the body cavity as a sheath, or (and I apologize for continuing with the breakfast meat imagery) a bit like a sausage casing. Using this organ, electric catfish of the genus Malapterurus can produce a discharge in the 300 to 400 volt range. This is enough of a wallop to discombobulate small fish for food, or to defend itself. The shock isn’t fatal to humans, but the jolt from a good-sized fish is guaranteed to be persuasive at getting you to let go of it pretty damn quickly.

These fish, and their electrical capabilities, were familiar to the people of ancient Egypt. Texts from nearly 5,000 years ago refer to electric catfish as the “Thunderers of the Nile”, and are among the earliest known acknowledgements of electrical phenomena. Smaller fish were used in a medical context, their shocks recruited for treating diseases of the nervous system like some sort of proto-electroshock therapy. Larger fish were wisely avoided; with them, it would more with the sizzling, and less with the salving.

Saltwater environments have their fair share of electric fishes as well. One inhabitant beneath the briny waves is the electric ray, also known as the “torpedo ray” or simply “torpedo.” They are different enough from other rays to comprise their own taxonomic order, Torpediniformes, one of the four major groups of rays (the others being skates, stingrays, and sawfish). The name of the group is not inspired by the naval weapon, but rather, the other way around. The “torpedo” device borrowed its name from a common genus of electric ray, Torpedo, in reference to the weapon’s ability to “stun” enemy ships. And by “stun”, I mean “sink.” The name of the fish comes from the Latin word torpere, meaning “numbed” or “paralyzed” (torpor…get it?). So, perhaps obviously, the ray’s name does not come from any physical similarity to an actual torpedo.

If we’re going by looks, I’d start with “black flapjack” for this guy. Or “punctured tire.”

Torpedo rays inhabit coastal waters the world over, and are ambush predators, shuffling their flat bodies underneath the sand and hiding in wait for prey. A brief zap and a voracious gobble and it’s over for whatever poor, oblivious bastard drifts by; a case of “shock and maw.” Unlike in electric eels and catfish, the electric organ of the torpedo ray exists as two, horizontally-oriented stacks of electrocytes on either side of the head. The electric discharge flows from the bottom of the ray’s body (the side with the mouth), up through the electric organ towards the top of the body and out into the seawater above…which is conveniently the “dinner arrival zone.”
Saltwater is more conductive than freshwater, so torpedo rays can get away with lower voltages (under 200 volts) in their discharges, but have somewhat higher amperages. Shocks from the largest torpedo rays (Torpedo nobiliana, pictured above, can reach the mass of a grown man) can be excruciating, but are not fatal to humans.

Like the electric catfish, torpedo rays are known from antiquity for their electrogenic properties and their use in medicine. Their role was mostly as a kind of anesthetic, since their shock would temporarily numb the patient. The Romans occasionally used them to treat headaches, and the ancient Greeks even used them to block out some of the pain of childbirth, because apparently that whole ordeal isn’t stressful enough for Mom without the experience of being smacked with slimy jump cables thrown in. It is unknown if any of the children were imbued with Magneto-like superpowers from the ray’s electricity…or powers like that kid in “Powder.”
The Greeks also employed the services of the torpedo ray in surgery, where it could be used as a localized anesthetic. Torpedo rays were evidently a lot like Flintstonian appliances in Greek society, electrocuting away the pain. Morphine? Try more-fin.

“Forceps, please…scalpel…fish.”

Another group of ocean-bound electric fishes are the stargazers (family Uranoscopidae). They live a life much like the torpedo rays, shallowly submerged in the sand on the continental shelf, hungrily awaiting prey to unwittingly swim by. They are squat-bodied monstrosities, with massive, forever-upturned faces (hence the name “stargazers”), primed and ready to strike upwards from the sand with their rapidly extendable jaws. Based on their frozen expressions, they also appear to be perpetually in a foul mood.

Your move, Grumpy Cat.

All stargazers are venomous, possessing two hollow spines behind the eyes to deliver the toxic cocktail when attacked…or accidentally stepped on by a soft, squishy, human foot. But, apparently this shit wasn’t impressive enough for a few species of stargazer, which have also evolved small electric organs derived from muscles in their damn faces. The shock put out by this turd-with-attitude isn’t much compared to the other fish previously mentioned, but it certainly helps stun small fish in that fraction of a second before the stargazer can shoot its toothy gob upwards to vacuum the unfortunate sucker in. It’s of no danger to animals as big as us, and run-ins with the jolt of a stargazer are more surprising than painful; less like grabbing a high-voltage fence and more like getting unexpectedly smacked in the chest with a basketball. For humans, its phaser is set to “stun.”

One species in the genus Uranoscopus even has a tag of skin on its lower jaw that it wriggles as a worm-like lure for small fish, getting them just close enough to electrocute and devour. This is kind of like advertising a garage sale, and then when the first curious visitor arrives at your house, you jump out of the hedges, zap him with a taser….and then eat him? Maybe it’s not a perfect analogy…

Bioelectrogenesis on the organismal scale has evolved multiple times in very different groups of fish, living in different parts of the world and in varied habitats. This “funneling” down into shared evolutionary strategies among independent lineages is a remarkable example of convergent evolution, and it was something that Darwin took care to note in his Origin of Species. From the cells of our most vital of tissues, to the beauty-deficient stargazer, to the genuinely deadly King of the Knifefish, the “spark of life” shares space with something far more literal. Life is an uncannily clever tinkerer, and bioelectrogenesis is just one spectacular representative of a great multitude of tools that have been intricately carved out by the tireless processes of evolution.

Image credits: Lightning, electric eel, electric catfish, surgeons, torpedo ray, stargazer

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.