Eel Life History

Eel Life History

The eel is a long, thin bony fish of the order Anguilliformes. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history. Although there have been more than 6500 publications about eels, much of its life history remains an enigma.

The European eel (Anguilla anguilla) was the one most familiar to Western scientists, beginning with Aristotle who did the first known research on eels. He stated that they are born of "earth worms", which emerged from the mud with no fertilization needed — they grew from the "guts of wet soil". For a long time, nobody could prove Aristotle wrong. Later scientists believed that the eelpout Zoarces viviparus was the "Mother of Eels" (the translation of the German name "Aalmutter").

In 1777, the Italian Carlo Mondini found the creature's gonads and proved that eels are fish. In 1876, the young Austrian student Sigmund Freud dissected hundreds of eels in search of the male sex organs. He had to concede failure in his first published research paper, and turned to other issues in frustration.

Until 1893, larval eels — transparent, leaflike two-inch (five cm) creatures of the open ocean — were considered a separate species, Leptocephalus brevirostris (from the Greek leptocephalus meaning "thin- or flat-head"). In 1886, French zoologist Yves Delage kept leptocephali alive in a laboratory tank in Roscoff until they matured into eels, and in 1896 Italian zoologist Giovanni Battista Grassi observed the transformation of a Leptocephalus into a round glass eel in the Mediterranean Sea, and recognized the importance of salt water to the process. Despite this discovery, the name leptocephalus is still used for larval eel.