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No one can figure out how eels have sex - Lucy Cooke

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From Ancient Greece to the 20th century, Aristotle, Freud, and numerous other scholars were all looking for the same thing: eel testicles. Freshwater eels could be found in rivers across Europe, but no one had ever seen them mate and no researcher could find eel eggs or identify their reproductive organs. So how do eels reproduce, and where do they do it? Lucy Cooke digs into the ancient mystery.

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TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Lucy Cooke
  • Director Anton Bogaty
  • Narrator Adrian Dannatt
  • Animator Anton Bogaty
  • Storyboard Artist Anton Bogaty
  • Sound Designer Jarrett Farkas
  • Music Jarrett Farkas
  • Director of Production Gerta Xhelo
  • Editorial Director Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Editorial Producer Dan Kwartler
  • Script Editor Dan Kwartler
  • Fact-checker Eden Girma
  • Special Thanks Shameka Williams
  • See more
Additional Resources for you to Explore
There are over 400 different species of eel. They can be found in freshwater and saltwater. Eels are fish that look very similar to snakes, but lack scales. They have fins and very sharp teeth. They can be found hiding between rock and crevices in order to surprise their prey. They also provide protection as eels have many predators which include fish, seabirds, racoons, and humans. Eels have even, historically, been regarded as a European delicacy.

So what makes these animals so interesting? We have no idea how reproduction specifically occurs in the eel. There are a couple of facts that we do know about eel reproduction. When ready to reproduce, eels travel to saltwater. We also know that the eel’s life cycle comprises five unique stages. Fertile eggs develop into leptocephali, a young larvae. The larvae, using currents to travel back to the coast of Europe, eventually become a glass eel. This phase can take a couple of years. Eventually, they enter the third phase becoming elvers. The longest stage of an eel’s life can last anywhere from five to 20 years. This is the yellow eel stage. The final stage is the silver eel stage, in which the eel makes its journey back to the Sargasso sea to spawn and die. It is in this final stage that reproduction is believed to occur.

There have been many ancient theories attempting to solve the mystery of where eels come from, but we still don’t know the answer. It was even believed that eels were born from sand, a debunked myth that Lucy Cooke explores in her book The Truth About Animals. What is more perplexing is no one has ever seen an eel spawning or an adult eel in the Sargasso Sea. We have found the youngest, and smallest, eels there which leads us to believe that the Sargasso Sea is their birthplace!


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About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Lucy Cooke
  • Director Anton Bogaty
  • Narrator Adrian Dannatt
  • Animator Anton Bogaty
  • Storyboard Artist Anton Bogaty
  • Sound Designer Jarrett Farkas
  • Music Jarrett Farkas
  • Director of Production Gerta Xhelo
  • Editorial Director Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Editorial Producer Dan Kwartler
  • Script Editor Dan Kwartler
  • Fact-checker Eden Girma
  • Special Thanks Shameka Williams
  • See more