|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.