The eel

The European eel is a remarkable fish. Like all European eels, it hatches in the Sargasso Sea in the Atlantic Ocean, east of Florida. From there, it sets out on a journey of thousands of miles to freshwater habitats across Europe, including rivers such as the Rhine. Along the way, its body goes through several transformations until it eventually takes on the familiar form of an eel in Europe’s rivers and lakes.

Once it reaches sexual maturity, the eel makes the long journey back to its birthplace to reproduce. Today, the European eel is critically endangered due to habitat loss, water pollution, and overfishing.

1. Egg
European eels spawn in the Sargasso Sea in the western Atlantic Ocean. Their transparent eggs are only about one millimeter in diameter. Fertilized eggs can be recognized by their prominent oil droplet. The larvae hatch about 48 hours after fertilization.

2. Leptocephalus larva
When it first hatches, the larva looks nothing like an eel. It is transparent, ribbon-shaped, and only 5 to 7 millimeters long. Its leaf-like shape is reflected in its German name, Weidenblattlarve, which means “willow leaf larva.” In fact, it was once thought to be a separate species of fish. For about three years, it drifts with the Gulf Stream toward Europe.

3. Glass eel
About 100 kilometers off the coast of Europe, the leptocephalus larvae develop into glass eels. They now have the familiar shape of an eel, but are still transparent and much smaller, measuring about 7 centimeters long. At this stage, they begin their migration into rivers.

4. Elver
As the young eels begin their journey upriver, their skin gradually turns brownish black. Once they develop this pigmentation, they are known as elvers. At this stage, they are about 10 centimeters long.

5. Yellow eel
After spending some time in the same body of water, the eel enters the yellow eel stage, with a dark back and yellowish underside. Yellow eels can even reach lakes with no inlet or outlet because they are able to wriggle short distances over land. For the next several years, they tend to remain in the same area as long as there is enough food. They can grow to more than 130 centimeters in length.

6. Silver eel
After no more than 20 years, the eel’s underside turns silver as it enters the silver eel stage. It then begins its journey back to the Sargasso Sea to mate, spawn, and die. During the year-and-a-half journey, the eel stops eating and its digestive tract regresses, while its reproductive organs develop.