I heard about The Book of Eels: Our Enduring Fascination with the Most Mysterious Creature in the Natural World by Patrik Svensson from a patron at the library, and the title alone was enough to pique my interest. Finally, at a loose end for an audiobook recently, I found that I'd made a note of this title and it was available to borrow, so I went for it. I enjoyed some parts immensely, while others were distinctly off-putting. Mostly the off-putting parts involved detailed descriptions of ways to kill an eel (luckily a minor part of the book) and occasionally ways they would ensnare themselves in fishing lines (also mercifully a small portion of the tale, though there is much eel fishing). Possibly I was also a little discomfited because I could picture the movement of eels fairly well thanks to this weird article from the New York Times about moray eels (worth looking at for the captions to the photos, if nothing else).
The most wonderful parts reminded me of H Is for Hawk by Helen Macdonald, which I enjoyed thoroughly about five years ago; that is to say, sometimes The Book of Eels offered a marvelous combination of fascinating facts about eels with moving nature descriptions and deeply-felt personal history, mostly of the author as a child with his father. Eels are enigmatic creatures, unwilling to yield their secrets to researchers, despite their ongoing efforts, which adds to their allure. The Book of Eels offers a brief glimpse into their world.