When is an eel, not an eel? In fact, our tanks are home to a great manu fish that we call eels, but that are nothing of the sort - or at least, they are not true eels or anguilliforms, in the phylogenetic sense. There may be other grounds for defining them as eels - if the word 'eel' is taken simply to mean, any slender and rounded fish, then it is not mistaken identity. But the fact remains these fish have not very much in common with the archetypal eels. And they would still be fishes, but there are also 'eels' that are not fishes at all, but amphibians. Among them are the doubly mis-named 'Congo eels' of the genus Amphiuma. As a young child, I remember meeting a congo eel for the first time, and feeling perplexed; even to a child it was obvious to me, this was mo eel. Was he a lungfish? That was not correct either, and I had to search my books to find what he was. He was actually related to newts!
These amphibians do dot come from the Congo, or anywhere near Central Africa. If only aquarists referred to amphiumas as Congo eels, it would be easy to attribute it to a simple.matter of miscommunication or misunderstanding: amphiumas are also called 'conger eels', after a namesake saltwater fish (the true eel Conger conger) that was already familiar to the European ancestors of white North Americans, and is similar in its strength and appearance. However it is also the case, that fishermen call these animals Congo eels (or snakes) as well as conger eels. Needless to say the Amphiuma is native to North America, and has never lived anywhere else, so it has no special connections to the black race. But Americans used to use the word 'Congo' to denote anything that was 'negro', so it's tempting to associate their seemingly inappropriate geographical moniker, as relating to the blacks in the southern states in the US - the translocated slaves and freedmen inhabiting the same, sweltering bayous. I cannot think of any other connection of amphiumas to things 'Congo'.
Of course these supposed eels are in fact big salamanders, bearing the exterior appearance and behaviors of an eel-like fish. It has been argued that they more closely still resemble the unrelated lungfishes, called lepidosireniforms, that live in similar habitats in Africa and South America, but not in North America. Three species of the genus Amphiuma are recognized; but the most familiar of them in the pet trade, is the two-toed amphiuma, Amphiuma means. This is a burrowing, air breathing animal from shallow, static freshwater habitats, and less often, sluggishly flowing streams. Amphiuma habitat is richly vegetated, and yields many available prey for the hungry salamanders. For like most aquatic salamanders, A. means are benthic carnivores that consume prey such as insects, crayfishes, fish, frogs, and even smaller amphiumas, that are both caught from ambush and located whilst actively foraging. All of the three species of Amphiuma are native to the more southern states of the USA, and A. means inhabits Coastal Plain habitats from southeastern Virgina to eastern Louisiana.
A. means is the largest of the three amphiuma species, and also the very longest salamander of the United States. Very large amphiumas can grow clear of a meter long, sometimes 116 centimeters or about 46 inches long; however this is not their average length as adults, and around 90 centimeters or 36 inches is much more normal for mature A. means. Those fossil amphiumids that are known from rocks of the the Late Cretaceous and early Paleogene, are relatively small amphibians, and the evolution of large size is relatively recent: the amphibians did not cease to evolve when the 'age of reptiles' came along, and the size of the big, modern amphiumas is remarkable, considering how small most other salamanders are. Amphiumas evolved when salamanders came to resemble the South American and African lungfishes, on a continent where all of the native lungfishes had already gone extinct. The same is true of another clade of large and sonewhat eel-like, North American salamanders, called the sirens, that live in the same habitats as amphiumas - but remarkably, they too are unrelated to amphiumas.
Amphiumas are strong and sinuous amphibians that possess four, true jointed limbs like those of land salamanders, although they are now rudimentary appendages, and some of their digits have been lost. This same evolutionary process has affected numerous kinds of four-footed animals, including the ancestors of the snakes. (Needless to say that although they may be called congo snakes, amphiumas are not related to snakes or any other snake-like lizards at all.) Amphiumas are known to communicate together using sounds, although they do not possess an eardrum. Unlike certain other aquatic salamanders, adult amphiumas do not retain their external gill structures into adulthood. For in their stagnant habitats the water has little dissolved oxygen, and it is particularly useful for animals to surface for a breath of fresh air, and therefore the lungs of amphiumas (and sirens) are large and very well developed. Anphiumas are still able to respire through their skins, in the typical amphibian fashion, but in warm water temperatures they rely on surfacing for atmospheric air.
Nonetheless, there are extremely aquatic amphibians and they will not ordinarily exit the water when they are kept correctly in the aquarium, although they can cross overland in wet weather, and can end up dwelling in remote ponds - a habit that is shared with some eel-like fishes, although we think of fish as strictly aquatic, whereas amphibians as turning into land animals. So as with eels and eel-shaped fishes, their aquarium lid should be secure against escape, but they will not require an aquaterrarium. Amphiumas are unfussy eaters, beyond their strictly carnivorous habits, and they will avidly devour defrosted 'prey' that, due to their having weak eyesight, they recognize as food using chemosensory cues. Nor are they very fussy about their water parameters; A. means favor waters with a circumneutral pH, although leaning towards the soft and acidic side. These amphibians are native only to the warmer regions of the Nearctic realm, where the summers are warm. Amphiumas can be housed at room temperature a of 18 to 22 degrees centigrade, but prefer 25 or 26 degrees, which is more like a 'tropical' than a 'coldwater' aquarium.
Although amphiumas are reclusive animals, they have sharp teeth, and they are able to inflict dangerous bites on human intruders when they are disturbed. Furthermore, they have a reputation as bad tempered towards other animals, which is exaggerated, but the risk is basically correct (like the similar reputation of African lungfishes). What is more, they are not limited to gape-limited predation, unlike many other carnivores. To my mind this is not the ideal animal to cohabit together with other species in an aquarium, but people who never heard the received wisdom about the 'snappy', passive aggressiveness of these animals, actually have housed them with fishes, sirens, or herbivorous turtles, and there were not always violent incidents. The key is understanding how the amphiuma uses available space; animals that are not seen as prey by the salamander; that will leave it alone; and will not compete for space with the beast, are the most likely to cohabit fine with an amphiuma. But to be on the safe side, I can't recommend this. Amphiuma means can also be kept together, but if so all the individuals must be similarly sized, because these carnivores are cannibalistic. Their only requirement as regards decor, is sufficient fine grained substrate in which to bury themselves out of view These are nocturnal salamanders so they need to retire away from bright light. Burrowing animals can of course uproot plants that are rooted into the bottom substrate, but floating plants and underwater epiphytes should be safe, and floating plants will help to diffuse any lighting from above for the comfort of the impressive and mighty amphiuma.