The eel is born in the Sargasso Sea, makes the long journey to the shores of Europe - and then, when the time is right, returns to Sargasso to reproduce and die. 

Humans still do not know why, or what happens when the eel returns home, because no one has ever seen an adult eel in the Sargasso Sea.

"How does it find its way back?"

The author Patrik Svensson's debut book "Ålevangeliet" has been translated into 33 languages ​​and enchanted hundreds of thousands of people.

He believes that the eel's enigma has an appeal.

- Science has for several hundred years tried to understand the eel and describe it.

How does it find its way back to the Sargasso Sea?

Eels refuse to reproduce in captivity, why do they do that?

It is listed as critically endangered, which means that it runs an extremely high risk of dying out in the wild.

This is what science is struggling with today: Why is it dying out?

Play the clip to learn more about the eel - one of the world's oldest fish.