This is a fascinating story that, since ancient times, has puzzled scientists and scholars. But today this mystery seems to be solved.
The European eel is one of those animals surrounded by mystery. Maybe it's because of its unusual shape, closer to a snake than a fish, or perhaps because of its nocturnal nature. The fact is that with such a unique fish, we can find wonderful adventures and legends in which scientists had to digg to unravel its mystery.
Any person, fisherman or not, cannot walk into the world that surrounds this fascinating fish and overlook the aspect of its reproduction.
How did everything start?
Aristotle knew two very important aspects that had to do with the spawning and the rearing of eel. The first was that they descend through the rivers for the annual migration to the sea and the second was that they have no sexual organs for reproduction. They also knew at the time that the elver is a baby eel.
Since the time when the philosopher made these observations till the late nineteenth century, most of the opinions about this fish passed through assumptions about witchcraft.
Isaac Walton, in his book "The Complete Angler" developed his own theory that " Eels may be bred as some worms, and some kind of bees and wasps are, either of dew, or out of the corruption of the earth”.
Possibly the origin of such beliefs is due to the observation of parasitic worms in the intestines of other fish or other animals, giving rise to the theory that those were young eels.
The real truth
Transparent and laminar beings were discovered first in the Mediterranean and later in the Atlantic Ocean. No one associated them with eels; they were named leptocephali.
What put researchers on the right track was when a leptocephalus was seen transforming into an adult eel. Following this discovery two Italian ichthyologists, Calandruccio and Grassi, proved at the end of the nineteenth century that these leptocephali were the larval form of eels.
However, the question about the origin of these small larvae was not yet answered (how did eel reproduce?). In 1904, the Danish national biologist Johannes Schmidt, who was definite about solving the mystery once and for all, began the odyssey of tracing the journey of these tiny fish aboard the boat Dana. Leptocephali were found in places like the Faroe Islands and the coast of Ireland and even from Cape Verde to Portugal.
Finally, after 11 years of research, Dr. Schmidt, demonstrated that leptocephali travel east to the shores of Europe and found that catches of these fish dwindled in size as they head towards the west and the south .
The end to this fasinating trip was in 1922, in the Sargasso Sea. And it seems that in this area, where the water is very deep, adult eels leave their eggs and die afterwards, finishing their journey.
There is little data about how he came back from there and his whole journey, but we do know he found out about the origin of eels in the end.
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A long story short
When the eggs hatch in the Sargasso Sea, these tiny beings (the elvers) measure around half an inch and go up to the upper layers of water to be swayed by the action of drift towards the northeast for one to three years, where the larger rivers become their new homes. That’s when they become eels. They go upstream the rivers to the upper courses, where they spend most of their lives. When they turn 14 or 15, they become silver eels, their guts disappear and the fat they had stocked is the only fuel that helps them go all the way down the river, cross the Atlantic Ocean and go back to the Sargasso Sea, where they leave their eggs and die.
Although it is one of the toughest fish in its efforts to go upstream the rivers, together with salmon, the fact is that, today, the obstacles this fish has to overcome are getting even more difficult.
Eels are capable of overcoming small weirs or dams of small dimensions, and even going outside the water for part of the journey. However, the construction of reservoirs with large dams, as well as the disappearance of rivers in their final stages due to drought, pollution and warm oceanic masses, are making it much more difficult to find this fish.
Given the serious shortage of eels, the governments of the countries affected are struggling to recover the species through the introduction of young specimens from eel farms (which are the ones satisfying the market).
The introduction occurs upstream of the large dams, sparing the eels the obstacle of the dams’ walls (which they would be unable to overcome by themselves). However, this action ensures only the first part of the journey goes well because they will still need to return to their original birthplace to breed.
From ancient times, eating eel has ben very popular worldwide. Over the years the price has increased to unaffordable rates due to overfishing and the scarcity mentioned. Depending on the area, the way the eel is prepared changes. For example, in Japanese cuisine it is prepared on the grill, in Germany they prepare eel soup and in Spain it is typical to prepare elvers with garlic and chilli.
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