Slideshow Showcase: Turning Facts into Stories

Eels are among the most fascinating and mysterious animals found in nature. They lurk in rivers and seas across the world. When one hears the word “eel”, one might be forgiven for picturing the electric variety, but did you know that electric eels are not true eels and are actually more closely related to catfish?

Are you ready to dive deeper into the enigmatic world of these elusive creatures? Read on for more interesting facts!

“Eel” is a catch-all term for over 800 species of fish that share the same elongated morphology. True eels fall into 5 main families, but the three most widespread are the common, conger, and moray eels.

The term “common eel” originally referred to the European eel (Anguilla anguilla). However, it is increasingly used as an umbrella term for other species within the Anguilla genus, such as the Japanese eel (Anguilla japonica) and the American eel (Anguilla rostrata). These three species are found in coastal, freshwater, and seawater habitats across Europe, Japan, and America.

For centuries, the origins of common eels remained shrouded in mystery, giving rise to wild speculation and theories. One such theory, proposed by the philosopher Aristotle, was that eels were spontaneously generated “within the entrails of the Earth.” This theory arose because juvenile eels were nowhere to be found, and eels lacked visible external sex organs.

Part of the mystery surrounding common eels in antiquity was their sudden appearance in rivers and lakes with no apparent source. Unlike fish that visibly reproduce in water, young eels seemed to appear out of nowhere.

It wasn’t until the early 20th century that scientists, while traveling westward, began to track European eel larvae. Upon reaching the Sargasso Sea, they discovered the larvae to be newborns.

From separate studies a few decades later, it was determined that American eels were also spawning in the Sargasso Sea. While they are very similar, they are a distinct species. This revelation remained unconfirmed until the 1990s.

Adult common eels possess the rare ability to migrate between freshwater and saltwater, a process made possible by undergoing physiological changes as they transform from yellow eels to sexually mature silver eels. This transformation led to the misconception that they were separate species, adding to their mystery.

When silver eels reach their spawning grounds, they mate, spawn larvae, and then die. The larvae use the currents north of the Sargasso Sea to drift either toward the North American coast or the European continental shelf, where they transform into glass eels. Japanese eels have a similar life cycle, but they journey to the West Mariana Ridge in the Pacific to spawn.

The transparent, nearly invisible glass eels were once believed to be a separate species due to the size difference between them and yellow eels. They then gradually make their way up rivers to freshwater, where the cycle begins again.

The diet of common eels changes throughout their life cycle. During the larval stage, they don’t eat at all. As glass eels, they feed on plankton. In the yellow eel stage, they bulk up by consuming small fish, invertebrates, and organic waste. On their final migration, eels don’t eat, relying instead on the fat reserves they accumulated during their yellow eel stage.

Most species of eel can breathe through their skin to some extent, but common eels are especially good at this to help them survive in oxygen-poor, murky water.

Adult common eels in Europe can reach 1.5 metres in length, but are usually around 50 centimetres when they reach maturity.

Overfishing and quality control issues have contributed to a 90% decline in eel populations in European rivers. As few as 200 eels made it to Norway in 2024, down from over 10,000 just a few years before.

Conger eels are found in temperate and tropical waters around the world. Because of their wide range and elusiveness , it is hard to estimate how many of them there are.

Conger eels are typically much larger than their common eel relatives, with some subspecies growing between 2 and 3 metres long. However, Californian conger eels are rarely longer than 60 centimetres.

Conger eels inhabit caves and crevices along the ocean floor. They use them for their ambushes.

Conger eels have long, muscular bodies, and some large subspecies can weigh up to 60 kg. Unlike common eels, they lack scales and have smooth slimy skin. They are slow swimmers but their snake-like shape allows them to manoeuvre along the creviced ocean floor with ease.

Like common eels, some American conger eels spawn in the Sargasso Sea, but closer to the ocean floor. It is believed that most species of conger eel do not travel far for spawning and mating, but because they exist deep in the ocean with little recorded evidence either way, it remains something of a mystery.

Conger eels are carnivorous, and use their powerful jaws to catch fish, molluscs, and crustaceans. They are ambush predators, preferring to wait for their prey to come to them before striking.

Moray eels are found in tropical and sub-tropical waters around the globe.

Moray eels vary greatly in size, ranging from 30 centimetres to 2.5 metres on average, with some exceptional specimens reaching 4 metres in length.

Similar to conger eels, moray eels like to reside in crevices and caves on the ocean floor, but they also inhabit coral reefs.

Moray eels are carnivorous, feeding on small fish, molluscs, crustaceans, and octopuses. Similar to their conger eel relatives, they are ambush hunters.

Moray eels have highly developed olfactory organs which give them the strongest sense of smell of any eel species. This is likely for detecting prey.

Although most species of moray eels are hermaphroditic, possessing both male and female reproductive organs, they still require two individuals to mate.

Perhaps the most “striking” feature of moray eels are their retractable pharyngeal jaws, with which they capture their prey. The moray grasps the target with its primary jaws, then launches its pharyngeal jaws from its gullet and pulls their victims further within the confines of their primary jaws, sealing their fate.

The pharyngeal jaws of the Moray eel are thought to be the inspiration for the Xenomorph’s jaws from the Alien movie franchise.

Electric eels are not true eels and are not closely related to them; they are more closely related to catfish. Despite them not being true eels, they are more than worth a mention.

Until 2019, it was believed that there was one species of electric eel in existence (Electrophorus electricus), but they found two new species in the same year, Electrophorus voltai and Electrophorus varii.

Electric eels can produce an electric shock of up to 860 volts to stun prey and defend themselves.

Electric eels use electric pulses to navigate the murky rivers of South America, as well as identifying potential prey.

Electric eels utilize three specialized organs in unison to generate electrical fields.

As discovered recently, electric eels can leap out of the water to deliver a more focused electrical shock through their chins to deter threats from above.

Unlike true eels and the vast majority of fish, electric eels breathe air. They take large gulps of air before submerging themselves in their murky, oxygen-poor river habitat.