Captive Care Notes: American Eel (Family Anguillidae)
American Eels are easy to keep in the aquarium as long as they are kept in the aquarium. Eels are amazing escape artists. By day, captive eels usually remain buried in the aquarium substrate, or under rocks or other ornaments. By night, they are restlessly active, and will try to eel their way out of the tank or up filter intake tubes, where they risk getting mangled by the filter's impeller blades. Eels are also fond of swimming up the outflow of "bio-wheel"-type filters and into the filter chamber. To prevent escape, the aquarium should be covered with a tight-fitting hood or canopy. If the cover includes a plastic strip that attaches at the rear, make sure that the strip is completely flush with the top of the aquarium and not turned up over tubes, air hoses, and other aquarium items that enter the tank. Cut openings in the plastic strip to fit snugly around tubes and hoses; should any openings remain, plug them with filter floss as if you were adding insulation to a drafty window or door. Fry guards are a must for filter intake tubes. Avoid the use of undergravel filters, since eels will swim down the lift tubes and get trapped under the filter plate. And if it doesn't interfere with tank aesthetics, an added precaution is to lower the water level a few inches from the top. Do not underestimate the eel's Houdiniesque talents. I'm sad to confess that nearly every eel I've kept has foiled my attempts to confine it. Even when I've thoroughly sealed the top of the tank, I will knock something loose during feeding or maintenance, or unintentionally leave the top open after feeding them before I go to bed. Given an opening, an eel will go through it.
As long as they stay in the aquarium, captive eels are exceptionally hardy and long-lived. In Sweden, a captive European Eel named Putte achieved celebrity status for living in various owners' tanks for 88 years. The eel's aquarium hardiness stems from its ability to exploit different habitats and types of food in the wild. As such, eels are not fussy about water conditions and will accept any aquarium fare. It's even possible to keep eels in unfiltered aquaria as long as they are not overcrowded and overfed, and partial water changes are performed occasionally. (Bait dealers and fish mongers are able to keep eels alive for lengthy periods in atrocious conditions.) Once adapted to aquarium life, eels will come out from their burrows as soon as food hits the water. I like feeding my eels live blackworms. I use a turkey baster to squirt the worms directly into the substrate, where the worms live until the eels find them. Eels will also perform a valuable service in the community tank by feeding on dead tankmates. Should a fish carcass get wedged unseen behind a rock, piece of wood, or other decoration, an eel will gladly strip it to the bone before it can foul the water. Given enough food, small yellow eels will usually leave living tankmates of the same size or bigger alone. But as they grow -- and they will grow quickly -- so do their appetites. If their food intake is not increased, they will start picking on other fishes at night, especially other bottom-living fishes, such as darters. When my darters' fins start looking ragged, I know my eels are hungry and not getting enough to eat.
If an eel does not come out at feeding time, it's best to assume it has escaped. Immediately check under the aquarium stand or cabinet and the surrounding floor area, then expand the search in widening arcs away from the tank. Since eels can travel short distances across land in the wild, it may have traveled across the room. Check under rugs, floor mats, and anything else the eel could hide under. If there is another source of moisture or water in the room, like a drain pipe or a sump pump, check there. If the floor search fails, then turn off the filter and dismantle the tubes while holding them over the aquarium. Check inside filter cartridges as well. These packets often contain trapped food and provide a snug hiding place for thigmotactic eels.
Should an eel make it to the floor, donšt despair. There's a good chance it is still alive no matter how desiccated it looks. This was demonstrated to me one morning when I found my Persian cat, Zeke, playing with a five-inch eel. When I removed the fish from the cat's mouth it looked like a goner, covered with cat fur and dust bunnies. There was no telling how long it was out of the tank and subjected to the cat's torture. But when I plopped it back into its tank I saw movement, not much, but enough to tell me it was still alive. It remained motionless for two days while it shed its cocoon-like coating of fur and dried slime. After that it seemed none the worse for the experience.
Another clue that an eel may have escaped is the performance of power or "bio-wheel"-type filters. If filter water flow has decreased, or if the filter sounds like it has run dry, then that's a good indication that an eel may be trapped inside its impeller housing or stuck in the intake tube. Again, turn the filter off and dismantle the tubes over the aquarium so that the eel, if it is unharmed, can safely slip back into the water.
The downside of keeping American Eels, aside from their inclination to escape, is that they will get too big to keep peacefully with other fishes. When that happens they will need to be kept singly in species tanks, or euthanized. They should not, under any circumstances, be released back into the wild, where potential aquarium-borne pathogens can be spread to wild fishes.
The eel's complex migratory life history obviously precludes them from spawning in captivity, although numerous attempts have been made to spawn them artificially with hormone injections. In Japan, aquaculturists have artificially spawned the Japanese Eel (Anguilla japonica), and raised the larvae to leptocephali on a diet of freeze-dried shark egg yolk supplemented with oligopeptide, vitamins and krill extract. Whoever succeeds in propagating eels on a large scales stands to become a millionaire many times over.
Collecting eels is almost as easy as keeping them. Netting elvers or small yellow eels is as easy as spending a few hours with a seine in just about any stream along the Atlantic or Gulf Coasts. Baited minnow traps also attract eels, but only large ones will remain in the trap (where they often gorge on other trapped fishes). Be sure that local regulations allow for the collection of elvers and yellow eels. Occasionally small yellow eels are available at aquarium stores, where I've seen them labeled as the more exotic-sounding "Sargasso eel." Coastal bait shops are also a good source for yellow eels, but they tend to be on the large size and usually available only during striped bass fishing season, which runs from April to December depending on the region.