Monday, June 27, 2011

Freshwater Eels

From willow-leaved larvae to snakelike adults, eels have interested and bewildered us for a long time. Even today, they still have many secrets, some of which we may never uncover.

The jaw-dropping story of European and American eels starts, not in the rivers where the adults are found, but in deep water in part of the western Atlantic known as the Sargasso Sea. In the case of the European eel, this is some 4,000 miles away from the home rivers of the adults. Larval eels (known as leptocephali) take up to three years to cover the distance from their place of birth to their eventual homes. For the American eel, the journey is much shorter, but it can still take the larvae about a year to complete the trip.

Breeding Grounds

 EelsGranted that endless many eels had been gotten, gutted, and consumed over the centuries, none was ever found with egg-filled ovaries, or ripe eggs, or even sperm inside them. The first of these discoveries had to wait until 1777, when developing ovaries were found in a female specimen. About a hundred years later, a mature male was found, followed, several years on, by a fully mature female. 

It had nevertheless been observed that at certain times of the year adult eels showed an irresistible drive to reach the sea, even slithering over damp ground to do so. Gradually, it was realized that eels bred at sea.


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