Electric Catfish, Part 1: Galvani

Stan Shebs/Creative Commons

by guest writer James Smith

My taste in pets has been characterized by various friends and family members as being “exotic,” “eclectic” and “just plain weird,” and I must admit that there may be something to their claims. Perhaps no animal better exemplifies the point than one of my favorite fish, an unprepossessing species from western and central Africa. Sluggish and dull-colored, perhaps best imagined as a finned sausage with two tiny, though functional, eyes and six whiskers at one end, it does not strike one at first glance as an exciting or dynamic aquarium inhabitant. In fact, one might be forgiven for wondering if it is even alive when glimpsed by day, resting on the bottom beneath a cave or driftwood.

The fish in question is the electric catfish—technically, there are two genera of electric cats, one made up of large species reaching nearly three feet in length and the other one of dwarf species under a foot long, totaling some twenty-odd varieties. Only a couple really appear in the aquarium trade with any regularity. As the name implies, these fish can generate a powerful electric charge by means of an organ made up of modified muscle cells, spanning the length of the body. A fairish number of fish possess some form of electrical organ, but in most of these fish, the organ is “weakly electrical”—that is, it is only useful for orientation, communicating with others of the same species, and detection of prey: given the small eyes, nocturnal habits and murky habitat of most electric fish, it is as vital to their existence as are their gills or fins. However, the electric cats—like a handful of other species, most notably the electric eel—is a “strongly electrical” species: that is, it produces a fairly powerful current—a modest-sized 20-incher can unleash up to 350 volts, though thankfully at a relatively low amperage—which can be used to stun or kill prey, or conversely, in the fish’s own defense against an attacker.

Electric catfish in the wild have been recorded at lengths approaching four feet and a whopping 44 pounds, although in aquaria this size is rarely attained and 20 inches is more likely the upper limit. Growth is not very rapid, or at least, does not seem to occur at anything like the headlong rate of, say, some of the larger cichlids. This suggests that these animals enjoy a long lifespan, even by the standards of large fish—and plenty of the bigger aquarium fish will comfortably outlive a large dog under ideal conditions.

My first electric cat, Galvani, was the mild-mannered but tough guy in a tank full of decidedly antisocial finned hoodlums. At the time I was running a 75-gallon tank where I would toss any fish that became too obnoxious and nasty for my 38 and 55-gallon jobs. I did notice that every so often, perfectly healthy and aggressive fish would go, literally overnight, into a sudden decline spanning the course of a few days, swimming erratically, being unable to stabilize in the water, and eventually dying, but I could not find anything to suggest disease or parasites. It was not until I observed Galvani’s encounter with a clown knifefish named Rajah—a large, predatory Asian species, which like the electric cat, can attain lengths of over three feet in nature, but averages about half that in aquaria—that I began to realize what had been happening.

Galvani was only about six inches long, while Rajah was easily twice that. While not big enough to swallow such a large meal, Rajah would attack and beat up fish far too big to eat, and he ruled the tank. Even my nastiest cichlids—red devils—feared him. So far, Rajah had left the catfish alone, but this particular evening, he spotted Galvani leaving his cave to munch up a juicy nightcrawler I had dropped on the bottom, and took action, arrowing towards the catfish with open jaws. There was, of course, no blinding flash, no crackling sound, but Galvani clearly unleashed his charge as Rajah was closing with millimeters to spare. The big knifefish stiffened and nosedived into a cluster of fake plants, gills pumping furiously. Galvani turned and wriggled back into his cave, dragging the earthworm, which he had not dropped during the whole episode. After some time, Rajah hauled himself groggily up into the water column, and more or less returned to normal by morning. He did, however, give Galvani a wide berth from then on.

As with venomous snakes, an electric fish has some discretion over the amount of voltage it unleashes, and would probably as soon not have to waste energy on something it cannot eat, so a defensive shock is designed to discourage, not necessarily kill, an attacker. Because Galvani ate pellets and the occasional earthworm or piece of frozen fish, I never saw him use his extraordinary weapon for killing prey. But I suspect that the fish who mysteriously died—all of them cichlids of one sort or another, and all young specimens around four or five inches—had received a defensive shock from Galvani and were simply not sturdy enough to withstand it, dying of stress or perhaps even some internal injury.

When I dismantled the tank, Galvani was still going strong and at last report, is still alive—when I last saw him he was perhaps fifteen inches long. If he has a lifespan comparable to some other big, slow-growing fish, he will be around for a long, long time to come.

15 comments:

  1. Electric catfish. Tapir fish. Glass catfish. I remember them all from my old wildlife encyclopedias; so many moments of my childhood spent flipping through its pages, dreaming of these almost magical creatures from faraway lands. I never imagined I would see them alive one day. Today, it seems, you can have even the most fantastic creatures in a tank.

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    1. I suspect it's more a case of fishkeeping becoming advanced enough to allow the upkeep of the more unusual types with relative ease; people are even spawning a good number of marine species--once assumed impossible to breed in captivity unless perhaps you were the New England Aquarium--in their own homes. (Personally, I've never gotten that much into fish and of the fish I enjoy keeping, most are too hostile or large to spawn in a home aquarium.) On the other hand, I've never bred any of my reptiles, either--just not into that aspect of the hobby. The only things I've ever bred were roaches and rodents, and as a fellow herper, I think you can guess why--although some of the prettier rats do get "pardoned" and wind up as pets if friends want them!

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    2. :D I understand... rats can be very cute when they want to.

      I know what you mean about fishkeeping being advanced now. What I meant was just to express my awe at the fact that creatures I once thought of as fantastic or legendary (to me, anyways) are now being kept in aquaria. It's maggic in a bottle to me.

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    3. This tapir fish you reference--would this be a mormyrid of some sort? I know them as "elephantnoses" but "tapir fish" would also suit them, and one actually bears the species name "tamandua." A favorite weird fish of mine was always the African butterflyfish--I kept a pair of those once, Mariposa and Monarch--and just watching them circle like sharks when they saw me coming with the crickets was hilarious!

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    4. Yes, I meant the mormyrids. I knew them as tapir fish cuz that's how they were named- in Spanish- in the books where I first read about them. :D

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    5. Figured it was something like that. :) Only one really has enough of a "trunk" to be compared to an elephant, so tapir fish is probably a better term...to complicate matters, one medium-trunked species is sold as "Congo dolphin" and the round-nosed, trunkless mormyrids as "baby whales"!

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    6. How big are these mormyrids?

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    7. Varies according to species--most of them seem to top out around 10 inches, but some of the larger types reach 18 inches or so...large, as aquarium fish go. They tend to be territorial animals with their own kind, and shy with other fish, so most aquarists keep them in species tanks or with top-water species that won't enter their domain. Mormyrids are among the "weakly electric" fish that use their electricity for harmless purposes. I never fooled around with them myself--they're finicky captives that rarely seem to accept anything except live food, chiefly worms, and I feel they're best left in the rivers unless or until we experience a breakthrough of the kind that's allowed for some of the more fussy saltwater fish to prosper in tanks...though I suppose if I had a tank in place and a trustworthy dealer assuring me an individual was feeding well, I might bend my principles. They're so damned unique, and as fish go, intelligent...

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    8. How can you tell a fish is intelligent? (Sounds like the beginning of a joke, but I'm serious.)

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    9. Allow me, James :D

      Tapir fish, according to what I've read, have a brain size comparable (in relative terms) with a human's. I don´t usually believe that larger brain is always indication of greater intelligence (some animals simply have enlarged brains due to an enhanced sense), but people who keep these fish also report they're pretty smart and exhibit play behavior (a lot more than other fish) which is linked to complex intelligence. As if that wasn´t enough, apparent pack-hunting has been reported for at least one species. They learn quickly and seemingly have a complex communication system based on electrical signals.

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    10. Affirmative. In general, the intelligence quotient in fish is a little hard to measure, but mormyrids are pretty sharp as fish go. While anthropomorphism doubtless factors in, large, long-lived and usually (but not always) predatory species appear to have a little more on the ball than say, neon tetras. Nearly all fish get into a routine (feeding time) but the larger fish seem to be a little more outgoing and interactive--even large goldfish, not generally thought of as bright animals, have a pretty good long-term memory: three months, I believe, according to a study conducted in Belfast. I wonder if this has something to do with the potential size and lifespan of these fish. To achieve spawning size, even at the rate they grow, large fish have to avoid all sorts of enemies besides man, and would have to be proactive about spotting and escaping such threats. This goes especially, I would think, for solitary or only loosely social species where the safety of a school or mass spawning is not an option.

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    11. Thanks, guys. This is fascinating.

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  2. Awesome write up James. I highly suspect, this could be your "calling" Highly entertaining and educational.

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  3. Thanks for giving me the chance to share this, Gordon.

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  4. My pleasure, James. Always happy to have good writing on the blog.

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