How the mysteries of the eel’s sex life have inspired a bestseller

“There’s a heron in the book, too,” Patrik Svensson calls over after we notice the bird perched in the willow tree under whose arches the writer is being photographed.

In The Gospel of the Eels, the 48-year-old journalist’s extraordinary, prizewinning book on “the world’s most enigmatic fish”, such coincidences happen a lot.

The willow he describes in the book – the tree under which he fishes at night with his father as a boy – reappears in a later chapter in the willow-leaf shape of eels’ larvae.

The bats that flit over their heads return, first in his account of a philosophy article about what it’s like to be one, and then in the work of an 18th-century Italian scientist and eel researcher that he explores.

And now here’s the heron – like the bird he describes flying silently overhead as father and son arise at dawn to inspect their fishing lines.

Svensson had doubts over whether readers would accept these strange recurrences, or indeed want to read a book about eels at all.

But even before it won Sweden’s August Prize last year, sales were taking off, and it is now on the way to becoming this year’s surprise US hit, helped along by laudatory reviews in the New York Times and the New Yorker.

“It’s amazing. You don’t expect anything like this to happen when it’s your first book and you are writing a book about eels,” Svensson admits. “I thought it was kind of nerdy.

“I wasn’t sure there was a story about my father,” he adds. “He was a very normal man in a way, and the kind of man that you don’t usually write books about.”

The willow leaves and bats came of themselves. “I feel like it was almost out of my control because I didn’t make these up,” he says, although they provided a welcome link between the story of the eels and that of his boyhood relationship with his road-builder father.

“That was when the two stories connected, and when I decided that I would allow myself to use these as metaphors.” But such is his skill that the echoes and parallels he finds never seem stretched. It’s as if the eel’s mysteriousness is snaking out, beyond its extraordinary life cycle and uncanny ability to confound scientists, and into the writing.

Both his vivid accounts of moonlit eel-fishing – his father hammering a thrashing eel to a wooden board with a five-inch nail through the head – and his treatment of science’s struggle to understand this mysterious creature are strong enough to have stood alone.

At the centre of the book is “the eel question”, the mystery over the breeding habits of a fish which seems to have no sex at all. It’s a question that has obsessed scientists since Aristotle, and which drew the 19-year-old Sigmund Freud to spend a month fruitlessly dissecting eels in search of their elusive testicles.

We now know that it is only in the fourth and final stage of the eel’s life cycle that they develop reproductive organs, before they make their journey to breed in the Sargasso Sea, northeast of Cuba.

Or we think that’s what they do. “You can call it a mystery, but it’s also just a crazy fact,” Svensson says, “but no one has ever seen eels breed, and no one has ever seen eels in the Sargasso Sea. It becomes a philosophical question: how do we really know the things we do?”

Svensson’s uneducated but animal-loving father had told him about the eels’ double journey across the Atlantic – drifting to Europe with the ocean currents, then powering back against them as mature eels.

“Just the name, the Sargasso Sea, sounded like a fairytale place to me, and he told me that they could be very old, and that started this fascination.”

But his interest, like the eels, lay lurking for decades until an editor at the culture section of the Sydsvenskan newspaper where Svensson works suggested “mysticism” as the theme for their Christmas 2012 edition.

“I had never thought about it before, but I just kind of blurted out, ‘Well, I could write something about the eels, they’re … quite … mysterious’.”

He went on to bring together his father, the Christian story and the eels, into a wonderfully playful essay (Aristotle’s belief in eels’ spontaneous generation mirroring the virgin birth, and the way they are skinned by being nailed to a wooden post, the crucifixion).

It was only when he began researching the book that he realised how many others the eel had caught in its slimy grip.

“I wasn’t just going to ask ‘what do we know about the eel?’, but, ‘how do we know the things we know?’. If you ask that question, you find all these amazing stories and characters.”

There’s Johannes Schmidt, the Dane who spent two lonely decades trawling the Atlantic for glass eels and larvae, slowly zeroing in on the Sargasso Sea. There are novelists like Günter Grass, Graham Swift and Sweden’s Fritiof Nilsson Piraten, for whom the eel serves as a potent symbol. How, he asks, did the 19-year-old Freud’s failure to find the testicles of an eel feed into his theories of human sexuality? “He looking through his microscope … and what he can see through the lens is no longer just an eel, it is also himself.”

When discussing Schmidt, he writes, “a person seeking the origin of something is also seeking his own origin”. And this is true for Svensson too. “For the eel, its lifecycle is never complete until it has returned to the Sargasso Sea, and I can relate to that,” he says. “Writing the book is a way for me to write myself back to my own Sargasso Sea.”

In the final chapter, there’s another coincidence, when he encounters an eel in the lake by his parents’ summer cabin. Neither father nor son has seen one there before. It is just after his father’s funeral, and it convinces him his father, in some sense, is still with him.

“There’s no meaning at all in those coincidences,” he admits. “But there is a meaning for me.”