THE’European eel it is a fish that lives in fresh water, but the adults come from various parts of Europe, including the Mediterranean, to reproduce they migrate to the oceanic environment, in the distant Sargasso Sea: the newborns then face incredible journeys up to 10,000 km long to return to the rivers. The biology and ecology of these animals remained largely unknown to scientists for centuries. Even today, some fundamental questions regarding the oceanic migration of adult eels remain unresolved, but are endangered by illegal fishing, climate change and dams.
What fish are eels?
Aristotle thought that eels were born from mud and studied their behavior and anatomy for a long time, but drew many incorrect conclusions. Due to its resemblance to a snake Often it was not considered a fish and for centuries its reproduction mechanism remained unknown since, unlike other fish, no one had ever found an eel with eggs inside it. For this reason, throughout history many zoologists spoke of “eel’s dilemma”.
Only in 1824 did a German scholar, Prof. Martin Rathke, describe for the first time a female eel complete with reproductive organs and in 1921 the Danish naturalist Johannes Schmidt, after over ten years of research in the Atlantic Ocean, managed to find specimens newborns in the Sargasso Sea. Only in very recent times, in 2021, an international team has traced the journey of adult eels from the Azores islands to the Sargasso Sea obtaining for the first time direct evidence of the movements along the last 2,500 km of the journey. Even today, the depth and speed of swimming or the route that the specimens follow is not known.
Where the European eel breeds: the journey and the metamorphosis
They exist 19 species and subspecies of the Anguilla genus distributed worldwide except the eastern Pacific and the southern Atlantic. However, the most surprising story is that ofEuropean eel (Eel eel) which lives in rivers and lakes in Europe, but reproduces in the Sargasso Sea in the north-western Atlantic.
Every year, after a long journey from the European and North African coasts, thousands of adult eels arrive in the Sargasso Sea to breed and lay millions of eggs in the deep ocean darkness. Tiny thread-like larvae with very small eyes and heads hatch from the eggs. In a short time they take on a flat and elongated shape similar to a willow leaf, completely transparent: this is the stage leptocephalus. The leptocephali dragged by the Gulf Stream begin their return journey across the Atlantic towards the Strait of Gibraltar and the European coasts. Newborns travel approximately 10,000 km to return along the coasts of the Mediterranean, accomplishing one of the feats of longer and more complex migrations in the animal kingdom
The journey lasts three years and in the meantime the larva grows and takes on the appearance of a small semi-transparent eel, similar to a glass fish: the Czech. From the coastal environments the Czechs begin to move up the river estuaries and transform into ragani morphologically the same as the adult but smaller (40-45 cm). Once they reach river and lake environments they change into eels yellowfish with a long and muscular body, with a yellowish brown pigmentation and a wide mouth, capable of swimming up rivers against the current in search of food. The yellow eel also spend a few years in rivers, lakes and canalsremaining on the muddy bottom and hunting mainly at night.
Eels are quite long-lived and in captivity they can live up to 80 years. They become adults between 10 and 15 years old and at this point, following an instinctive call, they undergo the final metamorphosis into Argentine eel and go down towards the sea. The reproductive organs develop, the body becomes darker and the belly silvery, the eyes large and bluish and it stops feeding to focus only on migrating towards the Sargasso Sea to reproduce. Upon arrival, it breeds… and dies.
Threats to the survival of these fish
Even if the epilogue is not exactly pleasant, at least the eel has fulfilled its reproductive task. Unfortunately, however, such an adventurous journey often ends in the worst possible way, before even arriving at the destination due to the illegal fishing or why animals come sucked and shredded by the turbines of hydroelectric plants. Since the 80s of the last century, this species it has suffered a 95% decline in numbers and is now in serious danger of extinction due to various threats: poaching, climate change which alters ocean currents, the presence of dams, barrages and hydroelectric plants along the rivers, the impossibility of breeding them like other fish. In the last twenty years they have been accomplished international efforts for the conservation of eels and today, a European project coordinated by Italy, called LIFEEL, is carrying out actions in an attempt to save them from extinction.
