Eelapalooza

Eels resemble snakes in shape, but they’re fish, not reptiles. They don’t have a prominent pectoral fin—those little fins beside the head of the fish that help with navigation—so eels appear even more snake-like with their wiggling movements.

Like snakes, eels also shed their skin when they grow. Also like snakes, eels are carnivorous predators.

That’s pretty much where the similarities end. Like all fish, eels “breathe” through their gills, extracting oxygen from the water and extruding carbon dioxide. While eels don’t have prominent pectoral fins, they do have helpful sort of mega-fin that runs along the eel’s back and sides.

Maybe the most interesting thing about eels is that nobody in human history has ever seen them reproduce. Seriously, this has been an ongoing mystery and an unsolved problem of sorts in biology for millennia.

Aristotle suggested that eels might be created by means of spontaneous generation. They seemed to appear out of nowhere, arising from the mud like something born in a myth. In Pliny’s Natural History a few centuries later, the prevailing theory was that adult eels would scrape little parts of them off by rubbing against rocks, and these little parts became new eels.

This last one isn’t as crazy as it might seem. Eels begin their lives as near-transparent larvae, like little thin slivers of what they will eventually become. In spite of this directionally lucky guess, eels remained very mysterious, and for more than a thousand years, Pliny an Aristotle were considered the best sources on how eels live and reproduce.

Eventually, pieces of the epic eel tale were uncovered, and it became clear as to why nobody had ever seen eels reproducing. They had had plenty of chances over the millennia—European eels, the ones Aristotle and Pliny were observing, could be found anywhere there was fresh water.

If there was a stream, lake, or river, there were probably eels. There should have been plenty of reports of eels being born into the world, but there weren’t any.

That’s because all the spawning happens somewhere else.

It turns out that two prominent species of eel—appropriately named the American eel and the European eel—congregate in the Sargasso Sea, a spot in the middle of the Atlantic ocean between the Bahamas and the Azores.

Every one of these species of eels will attempt this journey, barring any genetic anomalies. American and European eels swim thousands of miles to get out there in the middle of the water, where they have some kind of a massive eelapalooza, where only eels can get in.

During the party, the male eels release sperm into the Sargasso Sea, and the female eels drop millions of eggs each in there. How exactly the fertilization process works remains a complete mystery to us humans, but we do know that those little translucent slivers (larvae) emerge from the party, ready to live their best little eel lives.

The larvae are far too weak and tiny to travel thousands of miles on their own volition, so they hitch a ride on ocean currents to make it to their freshwater homes, like an apartment eels move into after they make their way out of the ocean. Once they approach fresh water, the eels morph into something more appropriate for swimming in this region called a glass eel, and as the eels mature, the process can begin again in a few years.

Oh! I almost forgot: we think the eels die once they reproduce. Sounds like one hell of a party!