Fact Check: How Do Eels Reproduce? Is It Really A Mystery?

Alright eels. Keep your sexy secrets. Image credit: Rostislav Stefanek/Shutterstock.com

Who among us hasn’t soaked in the bath wondering to ourselves in our most private moments, “how do eels reproduce?” It’s a question that’s been shrouded in mystery, but do we really not know how eels mate in the wild?

The answer is no, not really. Research has allowed us to track the love lives of European eels (Anguilla anguilla) and the American eel (Anguilla rostrata) as far as their spawning ground in the Sargasso Sea (a nursery ground that’s popular with juvenile sea turtles, too). But the Great Eel Reproduction Mystery endures because nobody really knows how they get there, or what they do when they arrive.

What do we know about eel reproduction?

While the intricacies of eel reproduction are something of a mystery in the wild, these animals have been used for research as well as farming. Studies from these contexts have enabled us to peek behind the curtain of eel reproduction, but they have only shone a light on small aspects of the mysterious interaction in captivity.

As for what happens on those thousands-of-miles-long migrations out in the big wide world? We’re still pretty stumped.

“There have been some studies that have given us insight into some elements of eel reproduction, but these are often limited to studying a single aspect of what is a very complex situation,” said ZSL Marine and Freshwater Senior Programme Manager and Chair of The IUCN SSC Anguillid Eel Specialist Group Dr Matthew Gollock to IFLScience.

“For example, swim tunnels have been used to determine energy use in the spawning migration, but these are unable to take into account the pressure associated with these migrations and also the diurnal movement within the water column.”

“There are also efforts to stimulate reproduction in the lab using hormone treated eels. This has led to successful spawning, but again, to what extent this mimics the wild is uncertain.”

eel reproduction mystery
The gyres at the Sargasso Sea make them a festival for the seaweeds for which they're named as well as a host of immature wildlife. Image credit: Wind Vector/Shutterstock.com

Why is finding out how eels mate in the wild so difficult?

If you’re slapping on a pair of flippers with the intention of settling the Great Eel Reproduction Mystery once and for all, we regret to inform you that solving it isn’t as simple as popping out to take a look. This is because of the weird and wonderful lives of eels.

“Anguillid eels have a complex life-cycle that involves migrations between continental waters where they feed and grow, and the open ocean where they breed,” explained Gollock, however, we are making progress.

“Tracking these migrations is challenging and expensive and as such there is only a limited amount of research that has been carried out on this. In the past 10 to 20 years our knowledge has increased greatly due to improvements in technology and, in the species that are most studied, such as the American, European and Japanese eel, we believe that breeding occurs below 500 meters [1,640 feet] and is influenced by a range of factors that we are only just beginning to understand.”

eel reproduction
European eels (Anguilla anguilla) undertake a 5,000-kilometer (3,107) spawning migration from Europe to the Sargasso Sea. Image credit: Rostislav Stefanek/Shutterstock.com

What theories do we have about the great eel reproduction mystery?

As for existing theories regarding the intricacies of eel reproduction, here too we are making waves but only a single hunch has been proven so far.

“Tagging studies have been carried out on several eel species and our understanding of where they breed is improving all the time,” Gollock told IFLScience.

“However, only the Japanese and Giant Mottled eel has been found at a suspected spawning site, and for other species we are still working to understand specific locations and associated conditions.”

For now, research continues into the mystery of eel reproduction, a goal which Gollock is driven by in his work on a joint project with the UK Environment Agency. It aims to tag European eels in an effort to better understand their spawning migration, but for now, at least, the eels’ sexy secrets remain safe.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.

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