So, what is the first thing that springs to your mind when you think of eels? Many of you will probably think something slippery and slimy, not to mention jellied! I’ve always found eels to be fascinating creatures – right from the age of eight, I’ve kept babies of a few inches, known as elvers, and eventually giants of 76cm/30″ plus.

I captured elvers on regular visits to the west coast of Scotland, at the mouths of rivers that emptied into the sea locks. The method was simple: I used to wait for low tide when the river was no more than 45cm/18″ at the edges. I often got sunburnt on my lower back as I removed huge boulders while gazing with anticipation into the water for basically anything that moved.

Sometimes as many as three or four 60-76cm/24″-30″ eels would squirm around my bare ankles before I seized one with both hands and hurled it out onto the sandy bank so I could observe it.

The head of the Gymnothorax tile.

This was the ultimate entertainment for me – I was never interested in the ‘normal’ things kids enjoy such as the beach and amusement arcades.

Incidentally, the eels I caught were Anguilla Anguilla, better known as the European eel, family Anguillidae. These incredible creatures are found across the British Isles in lakes, ponds, canals, and streams. Many become land-locked and grow larger than those that make their way down rivers fighting against the elements to reproduce in the sea.

Keeping Eels in Your Tank

Eels can be kept in aquaria and tolerate a wide temperature range from extremely cold to quite warm (about 21°C/70°F). However, the tank should be no smaller than 120 x 38 x 45cm/48″ x 15″ x 18″ with a good flow, unheated, dimly lit with large boulders on smooth, 3mm gravel as a substrate.

Females grow substantially larger than males, often reaching 90cm/36″ long, whereas most males are half this size. They’ll eat meaty foods such as large earthworms, lancefish, and cockles.

Eels usually get along OK with their own kind as well as other sizable companions such as perch, Perca fluviatilis, etc.

Swamp eels

Now to warmer climates to take a look at a creature known as the Swamp eel, family Synbranchidae, which comes from South America, Africa and South-east Asia.

The only similarity these fish have with the true eels (Anguillidae) is the word ‘eel’. They are instead far more similar in design and habit to many lungfish species.

The body is round and tapered, with little more than a ridge along the back which also runs along the underside of the fish. There are no pectoral fins, and tiny gill openings give way to a very efficient secondary breathing organ, not unlike the one found in walking catfishes of the family Clariidae.

The most commonly imported species is Synbranchus marmoratus. These are found in Central and South America and are usually sold in shops at around 20-25cm/8″-10″ in length. At this size, they look rather harmless with their light tan background and black speckles.

However, fed properly on small, chopped high-protein foods, they quickly grow and grow and grow into 90cm/3′ monsters with powerful jaws capable of crushing your finger. Small specimens will live with other fish, but I’d recommend that adults lead a solitary existence.

These eels are often referred to as Tulip eels – the way they hang in a vertical position with the head inflated resembles a tulip!

This is a bizarre sight, especially when several do so at the same time.

Another similar fish from Central America is known as the Blind Swamp eel, Ophisternon infernale (formerly Synbranchus infernalis). It has a plainer appearance with an almost pinky background and very fine brown speckles. It is commonly confused with its Asian cousin, Monopterus albus. Only an expert eye would be able to tell them apart.

Swamp eels are best kept in freshwater, though slightly brackish is tolerated well. Just like the primitive lungfishes of Africa (Protopterus sp), these strange eels bury themselves in the mud when the rivers are low with their heads pointing in an upward direction. From this stance, they can ambush prey such as water voles, frogs and fowl by picking up vibrations through the mud.

Stories tell of how the local Indians used to entice these eels from their burrows using the ‘chicken on a rope’ method. What happened was that an eel would snatch the chicken in its mouth and cling on for dear life, even as it was being dragged out of the hole to meet certain death at the hands of hungry Indians. I don’t know whether this has any credibility, but it sure sounds more than feasible.

Spiny eels

There is a group of eels that inhabit parts of Africa and Asia which have always made me smile because of their comical appearances. I am referring to the Spiny eels of the family Mastacembelidae, with the Tyre track eel, Mastacembelus armatus, and the Fire eel, Mastacembelus erythrotaenia, being their most commonly imported representatives.

I’m going to look at some of the smaller, more manageable, members of this group. Until very recently, all of this family were classified as Mastacembelus. Nowadays, modern technology provides scientists with the necessary equipment to study genetics in much finer detail, allowing for accurate identification of many different species.

These eels are becoming more and more popular in the hobby with the discovery of new specimens among the usual favorites, such as the Peacock and Clown species of the genus Macrognathus. One reason for this popularity is the manageable sizes, usually around the 20-25cm/8″-10″ mark in captivity, which makes them suitable for many community tanks. Although small tetras such as Neons and Cardinals will most certainly be on the menu, platies, swords, gouramis, and barbs, etc will be fine.

Spiny eels should be kept on a sand substrate no more than 2.5cm/1″ deep; any deeper and they will disappear due to their highly efficient burrowing technique. It’s also wise to avoid sharp objects as their skin is quite delicate and susceptible to fungal infections.

Great care should be taken when handling these eels. The word ‘spiny’ does exactly what it says: I’ve had my hand pierced more than once on the many sharp, short rays that make up the dorsal fin.

Spiny eels live a nocturnal life in the wild buried beneath the mud of rivers, only venturing out when the sun goes down to search for small aquatic life such as mosquito larvae, shrimps and small fishes. At the first sign of danger, they swiftly retreat into the soft mud, leaving behind little or no trace.

Provide plastic or clay pipes. Never use plant pots as the small drainage holes will trap these eels – I’ve seen too many die this way. Dim lighting is preferred with a gentle current from a mature filter.

The Peacock eel, Macrognathus siamensis, is perhaps the most commonly imported species. It originates from Asia, notably the Mekong and south-east Thailand rivers. It attains 30cm/12″, though I have never experienced one larger than 20cm/8″ in captivity.

A relative newcomer to the hobby is the Zebra Spiny eel, Macrognathus zebrinus, formerly of the genus Mastacembelus. These fish are said to reach 45cm/18″ in the wild, but I feel that 20-25cm/8″-10″ in captivity is quite an achievement for even the most dedicated fishkeeper. Most imported specimens are about 10cm/4″ long.

It’s found throughout Asia and Indonesia. The body is beautifully patterned with vertical stripes on a yellow-orange background, while the snout is longer and thinner than the previous species.

East Africa has some stunning representatives, notably Lake Tanganyika where many species are endemic. One of note is Aethiomastacembelus ellipsifer, formerly Afromastacembelus.

These eels have a lovely, broad, dark saddle-like pattern against a cream background, giving them a real exotic appearance.

Being a species from Tanganyika, they won’t appreciate the usual water chemistry associated with a community tank. I suggest this particular eel should be kept as an oddball in a Tanganyikan set-up with hard, alkaline conditions, say a pH of 8.5 and 18-20dGH.

The dorsal, anal and caudal fins make up an almost a continuous fin structure around the body, with only the dorsal area having hard rays.

In this family, the swimbladder is absent which is a common characteristic among many bottom-dwelling species of fishes, notably the gobies of the family Gobiidae.

‘Freshwater’ morays

Finally, there’s a family of eels normally only associated with marine environments. They are from the Gymnothorax part of the Muraenidae. The most frequently imported species is Gymnothorax tile, formerly known as Lycodontis tile.

These are found around the Indo-West Pacific, including the Philippines, India and Indonesia, where they congregate around estuaries and the mouths of rivers.

Aquarium subjects are best kept in brackish conditions, though I have to say that the ones in our shop are doing really well in freshwater.

Although these fish have a formidable bite, they are sociable not only with their own kind, but also with other species of fishes. A colleague keeps his with a Siamese Tiger datnioides, Coius quadri-fasciatus, and an Alenbatrachus grunniens, known in the trade as a freshwater lion or toadfish.

Food consists of cockles, whitebait, and mussels; prawns are also accepted. Just don’t expect new arrivals to feed immediately – they often need a month or two to settle in before they will accept food. Dimly lit tanks are best and provide plenty of hiding places. Cover glasses are a must.

G. tile have a dark to light grey background with fine, yellowish spotting. The mouth is large with extremely sharp, conical teeth. The external gill openings are tiny, more of a tubular orifice than the usual split type openings.

This species is said to top out at 60cm/2′ long, though I have doubts about that.

 

It’s a pity eels have had such a bad press, for they certainly make incredible aquarium subjects. They’ll get my vote every time!

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