What makes eels so slippery?

Among the most unsettling aquatic creatures is the eel. Its slick, slimy appearance defies the typical classifications we assign to water-dwelling animals, heightening our unease. Is it a snake? A fish? Or some bizarre fusion of the two?

In reality, the eel is simply a fish with an unconventional appearance. Its serpentine head and elongated body resemble a snake, complemented by a menacing face. Encountering one while snorkeling often leads to a quick retreat, especially after noticing its gaping mouth and razor-sharp teeth. However, the eel's mouth movements are merely its way of "breathing," not an act of aggression.

Eels inhabit almost every ocean and sea globally. The green moray eel is the most familiar species, but over 600 types exist worldwide [source: Gerber]. Belonging to the order Anguilliformes, eels use a unique swimming method called anguilliform locomotion. Unlike typical fish, their elongated, flexible bodies move in wave-like motions, with each segment tracing a figure-eight pattern. This full-body movement propels them forward, setting them apart from other fish that primarily rely on their tails for swimming.

Having clarified what an eel is, let's address what it isn't -- such as an electric eel. Despite their similar appearance, electric eels are not genuine eels. They are part of the knifefish family, capable of producing an electric charge strong enough to stun or even kill small fish.

Similarly, eels are not to be confused with slime eels. Considered a delicacy in certain regions, these creatures resemble small eels and secrete a dense, slimy mucus when disturbed. However, slime eels are actually hagfish, not true eels.

True eels, on the other hand, are undeniably slimy. The phrase "slippery as an eel" is often used to describe someone cunning or hard to pin down. But are eels truly more slippery than other fish?

The Eel's Slime Layer

Every fish is coated in a layer of slime, making them challenging to grasp by hand. This mucous, secreted from glands under their scales, offers protection against various threats. It primarily serves three key functions:

Osmoregulation: Similar to humans, fish are predominantly composed of water. They continuously exchange water through their gills to maintain an ideal biochemical balance, a process known as osmoregulation. The thickness of the slime layer influences water exchange—thinner layers permit more water flow, while thicker layers restrict it. Some researchers suggest this coating also enables eels to transition between saltwater and freshwater environments without harm.

Physical protection: The slime layer acts as a defensive barrier, making the fish harder to grasp. It helps smother pathogens or parasites attempting to penetrate the fish's scales. Additionally, the mucous shields open wounds from further injury and allows the fish to glide effortlessly through obstacles like coral or human hands.

Aerodynamics: The slippery slime coating enhances a fish's speed and agility in water. It smooths out the gaps between scales, creating a more streamlined shape—similar to how competitive swimmers shave their bodies to minimize resistance.

An eel's slime can harbor algae, which is why the common moray eel often appears green despite having dark blue skin. Additionally, eels have smaller scales compared to other fish. Combined with their elongated, snake-like bodies, this scale size likely contributes to their notably slippery texture.

The slime layer is vital to an eel's survival, and its removal can be fatal. Fishermen often use salt to strip away the slime and expedite the eel's death. Additionally, eel blood contains toxic elements. While eel is considered a delicacy in many cuisines, it must always be cooked thoroughly to neutralize the harmful proteins [source: Animal Planet].

Interestingly, a freshly killed eel can remain active for a while after death. Due to this and its slippery skin, chefs often secure the eel's head to a board to simplify skinning and filleting. Alternatively, you can skip the hassle and enjoy expertly prepared eel at your favorite sushi restaurant.

For more fascinating details about eels and other aquatic creatures, explore the links provided below.