Nederlands The mystery of the eel
The eel triggers a lot, among many people. It is a mysterious species of fish, the subject of many documentaries and books. The annual migration of European eels to the Sargasso Sea, swimming 6,000 km without eating, is unimaginable. Even more puzzling is the spawning in the ocean and the return of larvae. No one has ever observed exactly what happens in the Sargasso Sea, but we think it goes something like this.
After fertilization, within a few days a very small larva hatches from the egg, which still has no eyes and no jaws. Feeding on the yolk sac, a free-swimming larva develops in a few weeks and starts looking for food. Exactly what these larvae eat in the ocean is not known. After a few months, a new stage, the leptocephalus, develops from the larva. This larva, which is completely transparent and looks like an upright swimming willow leaf, makes the journey back to the European coast. Close to the coast, the glass eel develops from this, which swims into fresh water and grows into adult eels over several years. Eels can live in inland waters for more than 10 years. They do not reproduce, all they do is grow and become fat. Each year a certain fraction of the older animals swim out to sea (silver eels). Only then do they become male or female and develop sexual organs. When they arrive in the Sargasso Sea, all the reserve is used up and they are completely full of sperm or eggs.