European eels are among the most popular fish on a gastronomic level, but have been for several centuries a real pain in the ass for science, since researchers were unable to determine its origin or sexual characteristics.
Unlike many other commercialized and generically known species in Europe, eels were in fact fished only when they were adults and reached some specific river courses, apparently to reproduce. Furthermore, until the beginning of the last century, no one could boast of having seen an egg or a young eel in nature, so much so that the legend was born that these fish were born directly from the depths, just before reaching the rivers, and that they were devoid of gonads.
In an effort to discredit this rumor and effectively understand the biology of this species, a very important number of scientists and intellectuals tried over time to solve this mystery, including Aristotle, Pliny the Elder, Marcus Aurelius, Lucretius, Averroes, Dante, Hildegard of Bingen, Leonardo, William Blake, Newton, Darwin and many other illustrious names of Western thought.
Even Freud, widely considered the father of psychoanalysis and the analytical interpretation of dreams, at the beginning of his career tried to study these fish, visiting the medical practice in Trieste of his teacher (and dear friend) Carl Friedrich Claus, a follower of Darwin.
Once in Italy, Freud became convinced that to understand the biology of this species it was necessary to identify its testicles, to determine whether or not the species was hybrid. A goal that he achieved only partially, dissecting thousands of eels, before dedicating himself to his true passion: the exploration of the human mind.
Even today there are several aspects that we do not know about the reproduction of this fish, even if unlike Freud and many other geniuses of the past we have a new starting point. In 1904, Johannes Schmidt, a Danish professor, was tasked with tracking eels returning to the sea directly from Carlsberg, the same company that makes the beer. The idea was to create a new type of market, taking advantage of fish farming, which went well with the consumption of alcohol.
Due to the difficulty of the task, Schmidt had to spend years alone to accomplish this feat, managing to report the first eel leptocephalus – i.e. the juvenile form of the species – only in 1922, capturing the smallest leptocephalus he had ever seen, in the heart of the Sargasso Sea, Caribbean.
Following the first discovery, all scientists understood what the reasons for the previous failures were. All scientists who had tried to study the species had made the same mistake, that is, looking for young eels not far from the coast.
Schmidt’s discovery instead made it possible to establish that the various generations of this species never interbred with each other and that they were found in the most unexplored places in the ocean. In fact, while the adults lived in peripheral areas or in the internal seas, near the continental shelves, the little ones lived far from everyone, in the very heart of the Atlantic and the Pacific, while the newborns were even further inside, in the most isolated regions of the entire planet.
For Aristotle, Newton, Freud and many others it was therefore technically impossible to understand the biology of the species, given that they were looking for populations close to the continents, how could it be imagined that these fish could also be very long-lived, managing to survive beyond 85 years of age.
Today wild eels are among the most protected fish in the world and the farms in the Comacchio valley, in the Po, have made enormous use of the discoveries made by Schmidt and Freud.