This Fascinating Animal Has Entranced Scientists For Centuries
If you’re looking to dive deep into the fascinating world of eels and unravel an enduring zoological mystery, then The Book of Eels is your perfect guide.
You’ll learn about the European species, Anguilla anguilla, which has long piqued interest from scientific minds like Aristotle to Freud.
Discover why the 19th century sparked a craze to discover the eel’s testicles and how their sexual life might have influenced psychoanalytic theories.
Plus, understand why eels have such great dodging abilities – they’re so good at hiding they are rarely seen in the wild!
Not only that but also learn how their bodies go through transformations over time as well as likely having a very different experience of time than humans do.
All in all, you’ll have all the answers this enduring zoological mystery holds with The Book Of Eels.
The Fascinating Life Cycle Of The Eel – From Leptocephalus Larvae To Silver Eels
Eels have a complicated life cycle that spans four stages of development – from the day they hatch in the Sargasso Sea to their death in the same location.
This life cycle is made up of their evolution from Leptocephalus larvae, to glass eels, yellow eels, and finally silver eels.
During the first stage, a newly-hatched Leptocephalus larvae are almost flat and transparent; they are then transported across the Atlantic Ocean by the Gulf Stream until they reach Europe, where their bodies start to transform into glass eels.
At this stage, they develop fins on their backs and bellies and grow larger.
As they swim up European waterways, glass eels become yellow eels; these eels can now travel further, eventually settling down in lakes or ponds all over Europe and staying there for decades until something triggers them to migrate back towards the Sargasso Sea – where it all began – for reproduction.
As they make this journey back home, yellow eel ultimately become sexually mature silver eels.
When these silver eels make it to their destination, all of their energy reserves will be used up – but not for nothing – as it is here that they fertilize their eggs before passing away.
Aristotle’S Legacy: An Elusive Fish, An Enigma, And The Most Important Problem In Zoology
When it comes to the human relationship with eels, there is no doubt that it goes way back in history; Ancient Egyptians even mummified eels!
But our scientific understanding of eels didn’t begin until Aristotle.
He was one of the earliest scientists to conduct a systematic study into the animal and wrote a detailed account about the fish’s anatomy which was highly accurate and ahead of its time.
In addition, Aristotle posed an interesting question: How can we explain the sudden presence of eels in a dried-up pond after rain? He proposed that they were born from mud itself, something which his peers disagreed with but weren’t able to dispute.
This particular idea sparked scholarly debate for centuries afterwards and has become known as “the eel question”.
Even now, 2000+ years later, we still lack understanding of the life cycle of an eel, showing just how mysterious this creature really is.
So it’s clear that scientific interest in the eel goes all the way back to Aristotle and shows no sign of relenting any time soon!
Slicing Eels And Uncovering Sexuality: The Many Trials Of Sigmund Freud’S Early Career
For centuries, the eel’s reproductive system seemed shrouded in mystery.
Early theories claimed that life could simply appear out of nothing and some believed that flies spawned from rotting meat.
That is, until Francesco Redi in 1668 took these ideas to the test and proved them wrong!
From then onward, it would take another hundred years for us to discover that eels produce eggs too – with famed Italian physician Carlo Mondini being the first one to publish a treatise on the female eel’s reproductive organ and eggs in 1777.
However, we were still missing one piece of puzzle – what about the male eel? Where were its testicles hidden? Fast forward another 100 years later and researchers in Trieste, Italy had discovered an unidentifiable lobe in an eel.
This sent renowned marine zoologist Carl Claus a student by the name of Sigmund Freud to investigate further with more than 400 dissected fish over one month; unfortunately, they couldn’t confirm this lobe as a male’s testicle thus layering yet more doubts into the unknown reproductive biology of eels.
Remarkably, it turns out that our answer doesn’t lie in new elaborate discoveries but perhaps was hiding before us all along: 20 years later a sexually mature silver eel was found off Sicily which became evidence proving that eels reproduce just like other fish do – with eggs produced by an adult female and sperm coming from an adult male.
After centuries of searching and hypothesizing we had cracked the code!
Johannes Schmidt’S Epic Quest To Uncover The Mystery Of The Eel Migration
Johannes Schmidt was a Danish biologist who, in 1904, set out on a mission to discover the source of eels – a mystery that had eluded scientists for centuries.
Schmidt’s plan was to measure the sizes of eel larvae at various locations and track them back to their spawning ground.
Starting from the coasts of Europe, he trawled for eel larvae up and down the continent but wasn’t able to make much progress.
After sailing westward towards the Americas, he finally encountered small enough larvae that they had to be fresh hatchlings.
After nine years of laborious work, Schmidt had finally discovered the birthplace of the eel: The Sargasso Sea in the Atlantic Ocean.
Thanks to Johannes Schmidt’s untiring efforts, we now know where eels breed and that they migrate over 5,000 miles from Europe to the Sargasso Sea just to breed – something few other animals do.
Eels Navigate A 5,000 Mile Atlantic Journey With The Aid Of Powerful Senses And Instincts
The book of Eels explores the mysterious ways that these creatures navigate their way across the ocean to get to breeding grounds in the Sargasso Sea.
It seems they use a combination of instinct and senses to do this.
It is thought that eels have an incredibly powerful sense of smell, so much so they can detect just one drop of rosewater in a lake, which could explain how they find their way to the Sargasso Sea, either smelling it or using other eels as reference points.
In addition to their strong sense of smell, eel’s are also believed to possess a built-in compass and can even sense Earth’s magnetic field.
This allows them some degree of location awareness which may explain why they tend to group together near the Azores around halfway through their journey home.
This reason combined with other signals such as the smells along the way all seem to lead back home indicating that while they rely on senses during part of the trip, there must be some kind of internal map stored in their brains guiding them once they approach close enough, although exactly how this is achieved remains something of a mystery.
Eels’ Development Is Driven By Environmental Clues, Not Age
The strange thing about eels is that they don’t age like humans do.
In fact, their metamorphoses are triggered by environmental clues, rather than age.
This means that even if an eel cannot return to the Sargasso Sea to breed and fulfill it’s mission, it can still survive for decades without maturing sexually or growing in size.
We know this thanks to the example of a young boy in Sweden who released an eel into a well almost 150 years ago.
When scientists removed it from the well in 2008, they were surprised to discover that it had not grown any larger and its only transformation was bigger eyes to adapt to the darkness.
Similar results have been found in pet eels being kept in fish tanks, as they essentially put their development on hold while still alive.
Research done by scientists in Ireland also supports this: there is no clear age limit when it comes to metamorphosis – some mature earlier while others may take up to 57 years!
So what actually triggers an eel’s metamorphosis? Scientists aren’t entirely sure yet but we do know one factor – how much weight it has managed to put on.
Our understanding of the matter continues with further research but for now, we simply don’t know all of the pieces necessary for completing this puzzle!
Humans Threaten The Future Of The Eel With Overfishing, Parasites, Barriers, And Climate Change
It’s no secret that human activity is having an incredibly detrimental effect on eel populations around the world.
We’re seeing a rapid decline in their numbers over the last few decades, with as little as 5% of what was around back in the 1970s.
This is largely due to illegal or unregulated fishing, which targets glass eels at a very young age and deprives them of their essential feeding grounds.
Then there’s the risk of disease and parasites spreading from one species to another due to eels being transported across continents.
Add into this man-made barriers such as dams and hydroelectric plants, which can kill up to 70% of passing eels, and you complete the bleak picture of the future for these creatures.
The most serious threat facing them, however, is climate change.
As global warming alters oceanic currents, newly hatched eels may struggle to reach Europe and if they do not arrive there they cannot feed, metamorphose or return to the Sargasso sea to breed.
Many EU countries have now implemented measures such as building so-called ‘fish bridges’ around dams and power plants and freeing some glass eels caught back into the wild.
But even then things might still not be enough too save this species from disappearing altogether in just a matter of years – unless we humans realise our complicity in this disaster soon before it’s too late.
The Book of Eels provides a comprehensive, in-depth exploration of the mysterious life cycle of this remarkable species.
In addition to exploring the history and evolution of the eel question, it examines why eels are declining in number and what we can do to help save them.
At its core, the book delivers an actionable message: we must boycott glass eel consumption if we want to keep these creatures around for generations to come.
Glass eel fishing is especially bad since so many are needed just to make a single meal; buying them in restaurants or supermarkets only exacerbates the problem.
Ultimately, The Book of Eels serves as an important reminder that even though understanding eels is difficult, doing our part to save them isn’t.