How are baby eels made? We still don’t know

Eels exist, of that there is no doubt. Yet these slippery customers have never been spotted mating or giving birth in the Sargasso Sea or anywhere else.

Aristotle thought they came from earthworms. Others thought they spontaneously generated. And to this day, no one really knows precisely where eels are made.

Yet there are eels – lots of them.

Over the past century, a consensus has formed that American and European eels journey thousands of kilometres across the ocean to spawn in the conducive conditions of the Sargasso sea. In this vast, self-contained gyre of water in the western Atlantic, near Bermuda, the water is warmer and saltier than the surroundings. The newly spawned elvers then make their way home.

But this extraordinary mission is a matter entirely of inference, first drawn by Danish researcher Johannes Schmidt after a series of expeditions to the Sargasso a century ago. No adult eels have ever been caught spawning there. Until recently, none had even been seen en route. “Their migration remains a complete mystery,” says Melanie Beguer-Pon of Laval University in Quebec. Yet there must be something to the Sargasso tale, says Håkan Wickström of the Institute of Freshwater Research in Drottningholm, Sweden. “They must spawn there because the tiniest eel larvae are found there,” he says.

And so the story goes: on the brink of sexual maturity, eels leave the shores of Europe or North America for the depths of the Sargasso sea, where they engage in panmixia, a wriggling orgy of individuals randomly mating with each other. The resulting larvae mature into transparent “glass” eels as they make the return journey to spend their lives in river estuaries on their respective continents….NewScientist

 

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