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The Book of Eels

Our Enduring Fascination with the Most Mysterious Creature in the Natural World

By Patrik Svensson
13-minute read
Audio available
The Book of Eels by Patrik Svensson

The Book of Eels (2020) takes the reader on a zoological odyssey spanning thousands of years. It’s the story of the eel – a creature that has enthralled humanity with its strange and complex life cycle. Countless scientists have dedicated their careers to the enigma of this fish, which has evolved to undergo several metamorphoses over the course of its life and to endure a grueling migration across the Atlantic to breed. But the eel has proven to be an elusive creature, and there are still many secrets about its life that it seems intent on keeping to itself.

  • Nature lovers who are fascinated by strange stories from the great outdoors
  • Fans of mysteries that stubbornly resist explanation 
  • Environmentalists concerned about humans’ effect on the future of the eel

Patrik Svensson grew up near a stream in Sweden, where his father taught him to fish for eel. He’s now an arts and culture journalist for the Swedish newspaper Sydsvenskan. Patrik lives with his family in Malmö, a city in the southwest of the country.

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The Book of Eels

Our Enduring Fascination with the Most Mysterious Creature in the Natural World

By Patrik Svensson
  • Read in 13 minutes
  • Audio & text available
  • Contains 8 key ideas
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The Book of Eels by Patrik Svensson
Synopsis

The Book of Eels (2020) takes the reader on a zoological odyssey spanning thousands of years. It’s the story of the eel – a creature that has enthralled humanity with its strange and complex life cycle. Countless scientists have dedicated their careers to the enigma of this fish, which has evolved to undergo several metamorphoses over the course of its life and to endure a grueling migration across the Atlantic to breed. But the eel has proven to be an elusive creature, and there are still many secrets about its life that it seems intent on keeping to itself.

Key idea 1 of 8

The eel has a complicated life cycle that includes four stages of development.

What does an eel look like? Long, black, and a bit slimy – right? Well, that’s partly true, but it’s not the whole story. Actually, eels only look like this during the final stage of their development. An eel that resembles an aquatic snake is probably nearing the end of its life.

These fish spend most of their years in immature forms. Between the day they hatch in the Sargasso Sea and the day they die there, eels go through four stages of metamorphosis.

The key message here is: The eel has a complicated life cycle that includes four stages of development.

The eels’ journey begins in the Sargasso Sea, in the Northwest of the Atlantic Ocean. Here, in the warm, murky depths, their larvae – known as Leptocephalus larvae – first hatch.

Leptocephalus larvae look very odd. They’re completely flat, and their transparent bodies are out of proportion to their tiny, ill-fitting heads. 

As soon as eels are born, they begin their long journey east. The Gulf Stream carries them across the Atlantic and toward Europe. This migration can take as long as three years.

Once the larvae make it to Europe, their bodies change again. They begin to acquire the familiar serpentine form. Larvae become glass eels. But they remain small – not much longer than your finger – and they’re still almost entirely transparent. The tiny eels then move from salt water to fresh water and travel up brooks and rivers all across Europe.

As they swim up Europe’s waterways, the eels undergo another metamorphosis. They grow larger and more muscular; fins appear along their backs and bellies; and, for the first time in their lives, eels develop pigment. Glass eels become yellow eels.

Yellow eels will swim for miles, looking for a place to call home. Finally, they’ll settle down, usually at the bottom of a lake or pond. Once an eel has found a perfect spot, it can remain there for decades, until something – scientists aren’t sure what – tells the eel it’s time to reproduce. The fish then begin their long journey back to the Sargasso Sea. Along the way, they undergo their fourth and final metamorphosis; yellow eels develop into sexually mature silver eels. 

Remarkably, silver eels never feed. Their stomachs simply dissolve. All the energy a silver eel will ever need comes from its fat reserves. 

Finally, once the eels make it back to the fields of seaweed in the Sargasso Sea, they fertilize their eggs and die.

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