What is an eel? When most people say something is an "eel" they usually mean it is some sort of long, thin, sometimes-slimy fish. But, this actually isn't what it means to be an eel at all - even some of the eel-like animals at the Two Oceans Aquarium are completely unrelated!

There are about 800 species of true eels in the world. They are all members of an order of fish called Anguilliformes (which uncreatively means "snake-shaped"), and they all share five characteristics:

  • They all have elongated bodies.
  • Their dorsal (back), caudal (tail) and anal (belly) fins are fused into one long fin.
  • They swim by making waves with their body, which allows them to swim backwards and forwards.
  • They don't have pelvic fins (the fins most fish use for stability).
  • All eels (even the ones that live in freshwater) breed in the ocean.
 
A geometric moray eel at the Two Oceans Aquarium. Credit: Devon Bowen

Now let's take a look at some common "eels" and see if they actually are eels:

Moray eels

Moray eels are generally large, muscular fish with elongated bodies and vivid patterns and camouflage. They are unique among all animals in that they use their pharyngeal jaws (a second set of jaws that some animals have inside their throats to break up food) to actually catch prey by extending them through their mouths - a bit like the xenomorphs in Alien.

Credit: Geoff Spiby

Moray eels belong to the Muraenidae family, and are a member of the Anguilliformes order - the true eels. Their name "moray" comes from the Greek word muraina which actually just means "eel".

Verdict: IT'S AN EEL!

Pipefish

Pipefish look like small snakes with armoured-plate covered bodies and elongated snouts. They are poor swimmers, and almost always inhabit shallow environments like river mouths and estuaries. Male pipefish are great dads - each one has a pouch that it uses to carry the eggs until they hatch (although they do honestly eat the eggs when they get hungry sometimes, as dads are wont to do).

They belong to the family Syngnathidae, which includes seahorses and seadragons. So, despite their eel-like shape...

Verdict: NOT AN EEL!

Snake eel

Snake eels, like the ocellated snake eel that we have at the Aquarium, get their name from their resemblance to sea snakes - some of them even have elongated nostrils that look like fangs! They use their patterns and colours to mimic venomous sea snakes, which helps to deter predators. Many snake eels also give up their fins, allowing them to burrow easily to find prey.

The alternating dark spots of the ocellated snake eel resemble the pattern of the Stoke's sea snake, while it's yellow and black colouration resembles the tail of the yellow-bellied sea snake. Credit: Devon Bowen

Snake eels belong to a family called Ophichthidae (that means "serpent fish" in Greek), which is a member of the true eel order.

Verdict: IT'S AN EEL!

Ribbon eel

The most noticeable feature of ribbon eels is their spectacular nose - they use massive tubular nostrils to detect the scent of any nearby prey. Ribbon eels change colour as they mature. They start life as pitch black juveniles, with females turning completely yellow and males turning blue and yellow as they mature - like the one in our Skretting Diversity Gallery.

As you can tell from these colours, this ribbon eel is a male. Credit: Ingrid Sinclair

Flamboyant ribbon eels are actually a species of moray eel. Despite their resemblance to creatures of Chinese mythology, we can assure you that they are not actual dragons.

Verdict: IT'S AN EEL!

Cusk eel

Cusk eels, including kingklip which we all know and love in South Africa, are a diverse family of elongated fishes that are characterised by fins that run the length of their bodies, much like morays, and by barbels below their mouths. Most cusk eels are bottom-dwelling, at all depths - some even dwelling in the ocean's Midnight Zone.

A favourite among South African diners, kingklip are a regular display species at the Two Oceans Aquarium. Note its pectoral fins - a sure sign that this is not a true eel.

Kingklip and other cusk eels are all members of the Ophidiidae family, which means "snake family" in Greek. They are actually a member of the Ophidiiformes ("snake-shaped") order which includes a huge variety of elongated fish - but not eels. In fact, they are more closely related to tuna and seahorses than to true eels.

Verdict: NOT AN EEL!

Gulper eel

Gulper eels became famous last year when the weirdo below was caught on film. These odd fish are able to expand their huge mouths so much that they can consume prey many times bigger than itself! That might sound crazy, but in the deep ocean where they dwell, a gulper eel needs to be able to consume anything it can find.

Surely these alien animals can't really be eels though? Until recently, scientists thought that the order to which gulpers belong, Saccopharyngiformes (meaning "small bag throat shaped" in Greek) was distinct from true eels. However, genetic studies have found that they are actually derived from more "traditional" eels, placing them firmly in the true eel family.

Verdict: IT'S AN EEL! (Technically)

Hagfish

Long, slimy and weird - hagfish meet all the requirements to be eels right? They are the only animals in the world that have skulls but no spines. They also do not have jaws, instead they have teeth attached directly to strong mouth and throat muscles. There are a few other bits missing too, eg. stomachs, side fins, half of a heart, bones, etc. When threatened, hagfish are able to secrete huge amounts of slime which helps them slip out of tight spaces, and to suffocate predators!

The eel-like six-gill hagfish at the Two Oceans Aquarium.

Hagfish belong to the superclass Agnatha, the jawless fish, which means that not only are they not true eels, they only barely qualifies as being vertebrates!

Verdict: NOT AN EEL!

Garden eel

Garden eels are tiny, pencil-thin eels that burrow on the sea floor - resembling a field of grass from a distance. Their tendency to retract into their burrows when scared, with just their heads exposed and then "grow" as they regain confidence gives them the appearance of a growing garden.

These tiny eels belong to the conger family, Congridae - which comes from the Greek word for "gong" (and your guess is as good as ours how that relates to an eel). Congers are members of the true eel order, and although these garden eels are tiny, their close relative the European conger is the larges species of eel in the world.

Verdict: IT'S AN EEL!

Electric eel

Although not a sea creature - we know that most of you want to see this on a list of "eels". Well, we have bad news for you - electric eels do not belong on this list. Shockingly, the electric eel is actually a species of knifefish, a family of nocturnal fish which live in brackish and freshwaters of South America. Knifefish have long bodies and use undulations of their long anal fins to swim - electric eels have just gone a step further and use these undulations to generate electric currents.

An electric eel. Zzzap! Credit: Steven G. Johnson (CC BY-SA 3.0)

We know that this revelation may leave many electric eel fans feeling emotionally charged, but we've got bad news for the electric eel lovers...

Verdict: NOT AN EEL!

Do you have a favourite eel? Think something belongs on this list? Let us know, and be sure to see our eels (even those that aren't really eels) on your next Two Oceans Aquarium visit.

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