The Fascinating Life of Eels, Which Breed Only During Their Last Year of Life

The eel is very mysterious, and among its strange but fascinating attributes is how it engages in sex only during its last year of life, and only in a single place: the Sargasso Sea.

For centuries, nobody could determine how they reproduced or where. No one knew if there were male and female sexes. Only one man's determination, despite the dangers of war, dared to find out.

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Eel Breeding

Eels only breed in the Atlantic Ocean, specifically the Sargasso Sea. They actually do not develop sexual organs until it is their last year of life and they are on their way to this region. Both the American and European eels, even if they are different species, breed in this area exclusively.

Life Cycle of Eels

Eels have four distinct life stages. They give birth to leptocephalus or eel larvae in the Sargasso Sea. These larvae are willow leaf-shaped and drift along ocean currents. The European eel drifts eastward to Europe, while the American eel goes westward.

When they hit land, they become what are known as glass eels, with an eel shape but completely transparent. After going to freshwater, they metamorphose again and become yellow eels. They live as freshwater yellow eels for quite a long time, which can reach 85 years.

Later on, they suddenly swim back into the ocean and go back to the Sargasso. This is when they transform again to become silver eels.

The yellow eels are what most people get to eat, although many also eat the silver eel.

Breeding in the Sargasso Sea

Silver eels are very strange. They do not eat through their entire journey to the Sargasso Sea, which takes more than a year. It is when they develop sexual organs, start to swim in a different manner, and their eyes also change. Their last goal in life is to go back home and reproduce.

If an eel fails to go back to the Sargasso, then it does not undergo its final metamorphosis and does not mature sexually. Meanwhile, it can almost live forever in its intermediate yellow stage. Some eels go back to the Sargasso after only five to seven years, but others only go back after 60 years.

The Fascinating Life of Eels, Which Breed Only During Their Last Year of Life — The eel is very mysterious, and among its strange but fascinating attributes is how it engages in sex only during its last year of life, and in only a single place: in the Sargasso Sea. Pixabay

It is still unknown how American eels know how to go west and how the European eels know how to go east. It is also unknown how they can find their way back to the Sargasso to breed and die.

Nobody knows why they only breed in the Sargasso, either. It could be due to the temperature of the area, or its water's salinity or pressure. Researchers tried to breed them in captivity in aquariums and big tanks, but they have been unsuccessful.

The Discovery of the Eels' Birthplace

The birthplace of eels was discovered by Johannes Schmidt, a scientist from Denmark. He was determined to find where they breed by catching eel larvae, measuring them, and following their path as they become smaller and smaller in size.

He reasoned that if he can find the smallest larvae possible, that place could be the breeding area and birthplace of eels. He sailed the Atlantic Ocean, despite World War I raging at the time. It took him 18 years before finally finding larvae which must be newly hatched eels. This area was the Sargasso Sea.