Where do eels have sex?
Everything you didn't know you wanted to know.
Eels are a fricken mystery. You see, if you were to catch an eel and chop it up, you’d find not a single gonad! No eggs. No sperm.
This, of course, was the mindboggler of an age. Aristotle thought eels emerged spontaneously, from mud and rainwater. Pliny the Elder thought that new eels developed when old eels rubbed away parts of their bodies on rocks.
At 19, Sigmund Freud decided to take this mystery on. He spent the next month cutting up 400 eels, looking for testicles. He found none, and he gave up. If you’ve ever wondered who messed Freud up enough to come up with psychoanalysis, thank your humble eel.
Even today, we still haven’t witnessed a single instance of wild European eel sex.
The Extraordinary Life of Eels
Our story begins in the midnight depths of the Sargasso Sea. Here drifts a tiny, transparent leaf—not a botanical specimen, but the leptocephalus, an eel in its larval form.
Imagine a creature so delicate that sunlight passes right through its paper-thin body. The leptocephalus begins an epic journey, carried by ocean currents. For up to three years, these transparent travelers drift thousands of miles, sustained by microscopic feasts as they make their way toward distant shores.
The First Transformation
As the continental shelf rises to meet them, these oceanic drifters undergo their first metamorphosis. The flat, leaf-like form contracts and streamlines. Their bodies become cylindrical, their transparency earning them their new name: glass eels.
Still no larger than your pinky finger, these glass eels begin an impossible journey. They gather at river mouths in countless numbers. Their bodies adapt to their new freshwater environments, and, for the first time in their lives, they now strive against the tide.
The Great Ascent
Now the journey turns Herculean. Glass eels transform again, developing pigmentation as they become elvers—determined adventurers heading upstream. They climb waterfalls, wriggle through damp grasses, and squeeze through impossible passages. During wet nights, they may even leave the water entirely, squirming across meadows to reach isolated ponds and lakes.
They’re still light - surface tension allows them to stick to walls, and climb up sheer rock faces; an inch at a time.
The Long Wait
Once they’ve gone far enough upstream, eels settle down. Transformed now into "yellow eels," they might spend anywhere from five to twenty years—sometimes even fifty—in lakes, rivers, and streams. These are the eels we think we know—secretive bottom-dwellers, emerging at night to scavenge and hunt. These are the eels Freud dissected, and Aristotle theorized about.
The Silver Years
But when the time comes, yellow eels undergo perhaps their most dramatic transformation. Their eyes enlarge to better navigate deep ocean waters. Their sides take on a metallic silver sheen. Most remarkably, their digestive systems begin to dissolve, making room for developing reproductive organs.
These "silver eels" cease feeding entirely. Their stomachs have been replaced with testes. They start burning through energy stores, accumulated over decades.
When autumn rains swell the rivers, silver eels begin their downstream migration. What follows is one of nature's most remarkable migrations. European eels travel over 3,000 miles back to the Sargasso Sea. For months they swim, their bodies burning stored energy, their digestive systems continuing to atrophy as reproductive organs develop. By journey's end, they are little more than sacks of sperm and eggs.
Deep in the Sargasso Sea, back where they started, decades ago, as leptocephali, the silver eels complete their life cycle. Female eels will release millions of eggs, and males release clouds of sperm. Their depleted bodies, now empty, drift into the abyss.
The eggs they leave behind will hatch into new leptocephali, transparent leaves adrift in ocean currents, beginning the cycle anew.