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The Electric Eel - Strictly For The Specialist ...

Once upon a time, before the Board archiving spirited away many of my posts, I wrote a piece about the Electric Eel, Electrophorus electricus. In that post, I suggested that this was a fish that should be best left to a small hard-core of very expert fishkeepers, not least because large specimens can deliver a sufficiently powerful electric shock to fell a fully-grown water buffalo, and that anyone without a lot of expertise taking on one of these fishes was deranged. Well, I've found someone who isn't deranged, and who has two of them in an aquarium at home. This person is, and this should come as no surprise to several of my regular readers, one Richard Hardwick, the 'oddball specialist' from Practical Fishkeeping magazine.

Richard is one of those people who have probably forgotten more about fishkeeping than many will remember: his collection is decidedly eclectic, and includes a recently-acquired Hoplias lacerdae capable of amputating a hand with its gin-trap mouth! Back around December 2003, Richard wrote a piece about his then-recent acquisition of Electric Eels, and some of his remarks make interesting reading.

First, some necessary preamble. Electric shock capability apart, the Electric Eel is very much a 'specialist' fish, not least because of its size. A fully-grown adult can reach no less than seven feet in length. And, long before it reaches that size, it attains a body mass sufficient to become a self-propelled ammonia factory. A combination of large appetite and water-fouling capacity to match means that this fish will require both a truly huge aquarium for long-term captive maintenance, and a filtration system capable of handling the wastes. Large specimens can produce ammonia on an almost industrial scale, so take it as read that any filtration system for this species will involve high-capacity power filters and a regular turnover of considerable amounts of activated carbon.

Next, the fish is mainly crepuscular in habits (i.e., twylight active), some specimens are fully nocturnal, and thus acclimatising the fish to more human-friendly social hours will require the usual 'lights out' feeding régime for fishes with such habits. Furthermore, as its natural habitat consists of weedy root tangles in rainforest streams shaded by forest canopy, subdued lighting is the order of the day, which restricts the plant choices that can be used to furnish its aquarium. Those not interested in a 'purist' biotope setting can opt for the perennial Java Ferns on bogwood, and given that the aquarium needs to be large to begin with, beech branches can be used to great effect in creating a good simulacrum of its Amazonian home. If somewhat brighter lighting is used, to facilitate growing plants such as Amazon Swords, then floaring plants such as Amazon Frogbit can be used to create the shaded areas that the fish will appreciate. Water parameters are typical Amazonian ones: pH around 6.6, hardness no more than 10°dH and preferably a little below this. A temnperature of around 24°C should suit the Electric Eel fine.

Once acclimatised to a suitably furnished large aquarium, the Electric Eel becomes, upon learning that the owner regularly adds food to the aquarium, a bold and quite showy fish. Indeed, Richard Hardwick describes it as being capable of becoming a real pet, even taking food from an aquarist's fingers! Foods should be mostly animal in origin, preferably fish or mollusc flesh, and of course even a small specimen will readily eat anything that it can swallow by way of other fishes. Given both its appetite, and its electrical capabilities, the Electric Eel is destined to become the inmate of a species aquarium unless one wishes it to devour any other occupants!

However, maintenance of this fish will always require assiduous attention to safety issues. Firstly, the aquarium technology will need additional protection over and above the usual measures for large fishes, to protect it against being 'zapped'. The aquarist will also need to adopt measures for self-protection against the possibility of the fish unleashing a shock, which means that insulation measures will be needed for equipment such as gravel vacs and nets. Long rubber gloves are also a good idea when performing routine chores upon an aquarium containing this fish, and it might even be worth while considering earthing facilities for the aquarium just in case.

Reports of the fish's electrical capability vary, but one feature that is universally documented is this: the larger the fish, the larger the shock it can deliver. The typical figure quoted is 300 volts at 1 amp current per metre of fish, although some laboratory experiments with larger adults have revealed that some specimens can exceed this figure - one specimen was reported as delivering a 950 volt shock! Since it takes only 30 milliamperes of current crossing the heart to be lethal to humans, a fish capable of producing up to 950 volts at 2 amperes should be treated with a LOT of respect!

The electric generation capability of the fish takes up no less than 80% of its body length. Three divisions of modified muscle 'electroplates' are present: the main organ, the hunter's organ (these two combine to deliver the powerful shock that the fish is capable of) and a navigation field generator called the Sach's Organ, which gives the fish a 3-D 'world view' in dimly lit waters. The fat-based insulating tissue surrounding the electroplates is, Hardwick informs us in the article, used by native peoples as a rub-on cure for arthritis!

While the electrical apparatus is the principal focus of interest, the rest of the fish's anatomy is also unusual. The fish's principal organs (gut, kidneys, heart etc) are all compressed into a small region behind the head, and the vent emerged from the body at a point that is actually forward of the pectoral fins. There is no dorsal or caudal fin, no pelvic fins, just two relatively small pectoral fins and a very large rippling anal fin that is used for propulsion. Thus, as Hardwick notes, the term 'Electric Eel' is somewhat misleading: what we have here is actually a huge electric Knife Fish.

Respiration is another unusual feature. The Electric Eel possesses an accessory organ located in the roof of the mouth for atmospheric respiration: indeed it takes 70% of its oxygen this way. Consequently, an aquarium for the fish needs to be deep enough to allow it to take air at the correct angle, and there needs to be a good air space between the water surface and the aquarium cover, again with adequate ventilation to provide an oxygen supply. The anatomical features thus make the fish resemble very closely the Gymnotid Eels: here Hardwick claims that the fish is actually a bona fide member of the Family Gymnotidae, but my other reference works cite it as belonging to its own (albeit closely related) Family, the Electrophoridae (according to the Nelson, 1984 classification scheme), which resides adjacent to the Gymnotidae in the Order Gymnotiformes. Whether the Electrophoridae has now been subsumed as a Subfamily of the Gymnotidae I have yet to ascertain, but for now, I'll depart from Hardwick's notes and settle for the classification familiar to me until I am pointed in the appropriate direction. Regardless of the taxonomic issues, the fish is clearly a Knife Fish, possesses a readily discernible Gymnotiformes anatomy, but differs from the Gymnotid Eels in behaviour: it is possible to keep more than one Electric Eel together in an aquarium (Richard Hardwick has two, which he hopes will prove to be a male and female pair), whereas fishes such as Gymnotus carapo, about which I wrote another post, are completely incompatible with each other to the extent that larger ones will cannibalise smaller ones.

Hardwick informs his readers that while little is known about actual reproduction, males are known to engage in combat for the right to mate with females. Whether such combat involves electrical discharges is not reported, but it would not surprise me if this was the case. Having said this, Hardwick informs us that it is possible to keep several of these fishes together, provided of course that one has the colossal aquarium required!

The Electric Eel is also of interest to the medical profession. Hardwick mentions in his piece that scientists have discovered that the fish not only possesses the ability to regenerate damaged body tissue, but bone as well. How the fish achieves this is obviously of import to surgeons involved in reconstructive surgery, and it remains to be seen whether the fish provides future generations of surgeons with new techniques for rebuilding people maimed in accidents.

One final remark from Richard Hardwick is this: the fish becomes quite a handsome beast as it grows older, developing an orange blaze under the head contrasting neatly with its otherwise jet-black body. Juveniles tend to be a more muddy brown colour, with silvery spots when very young, and are thus somewhat less distinguished-looking. Richard's own specimens are 30 inches and 42 inches long respectively, but still have a fair amount of growing to do!

However, for those tempted to follow Richard Hardwick down the 'oddball' road and acquire one of these fishes, a conversation I had with the staff at the Chester Zoo aquarium in 1995 should provide ample warning of what this species is capable of. A newcomer to the staff failed to pay sufficient attention to the electric shock prowess of this fish, and was promptly given a lesson he wouldn't forget in a hurry. Fortunately, he survived, but the shock was powerful enough to throw him a distance of no less than 18 feet through the air. Very much a "don't mess with me" fish ...



Panda Catfish fan and keeper/breeder since Christmas 2002