The Incredible Journey Of An Eel

By S. Grant on Thursday, June 26, 2014
“I am an unpopular electric eel in a pool of catfish.” —Edith Sitwell

In A Nutshell

For Westerners, freshwater eels are a rather unappreciated fish and, if considered at all, are usually thought of as slimy bottom-dwellers that are better left alone. However, what many don’t realize is that eels have incredibly interesting lives, which includes a total metamorphosis and an incredibly long migratory journey into the open ocean.

The Whole Bushel

There’s no denying that eels, with their long, snake-like bodies, are somewhat off-putting; yet when we look past their hideous appearances, we find out they are rather remarkable creatures.

All freshwater eels are in the Anguillidae family and are one of only a few fish that are catadromous, meaning they spend the majority of their lives in freshwater but go to the ocean to breed. For centuries, scientists and fisherman had no clue that eels made this migration, and they even thought baby eels, found at sea, were an entirely different species. In their defense, it wouldn’t be hard to mistake eel larvae for something else, since they look nothing like adult eels. Larval eel are tiny, transparent, and have a leaf-like shape. Even when they get a little bigger, to what’s known as the “glass eel” stage, they still don’t look quite right, as they are flat, only about 8 centimeters (3 in) long, and still entirely see-through.

It wasn’t until the early 20th century that researchers finally figured out what eels are really up to and how their bodies change. What they discovered is every year, sexually mature American and European eels take a long trip (as long as 6,000 kilometers or 3,700 miles) out to the Sargasso Sea, an area of the Atlantic Ocean that’s east of the Bahamas and southwest of Bermuda. They only have one mission on this voyage, which is to mate and lay eggs. They don’t even stop to eat along the way. In fact, their guts completely dissolve during the trek, so they couldn’t eat if they wanted to. Aside from losing a gut, they also optimize their bodies for the ocean environment by taking on a silvery sheen and expanding the size of their eyes.

After spawning and selflessly finishing their life’s purpose, the exhausted eels die at sea and leave the offspring to find their own way back home. It can take the young glass eels one to two years to reach the coastline and prepare to make their way into freshwater. But, before getting there, they once again change shape and become rounder, darker, and a bit more eel-like. At this stage they’re referred to as elvers and are about 8 centimeters long. During the spring, the elvers make the laborious swim upstream.

Neither the coming nor going migration is an easy feat for the eels, and they’ll often go to great lengths to get past barriers. They’re known to pile on top of each other to make their way over rocks, dig through the ground, and even traverse across dry land. The fact that they’re covered in slime makes it easier for them to slip and slide their way around. Still, many eels don’t survive the journey out to sea or back in, as they face a host of predators, get stuck in man-made obstacles, or end up in Asian fish markets.

Those that do make it can live as long as 15 to 20 years in freshwater before reaching sexual maturity and then taking their own noble voyage out to the salty breeding grounds.

Show Me The Proof

Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, by Ross Piper
The Independent: The great eel migration: One million to swim to Britain in one night