But for many marine biologists, the deep sea's biggest mysteries did not lie in the elusive minds of octopuses or the secrets behind a Greenland shark's 272-years-long life.

Instead, the ocean's deepest secrets lie with eel sex -- and reading even a little about it may have you tearing your hair out too.

For a very long time, we had no idea how eels made other eels.

We suspected European species all flocked to the Sargasso Sea around breeding season thanks to magnetic pulls, and that the event seemed to have something to do with eels' confusing life cycle.

Previous experiments involved injecting sex hormones into sexually premature eels (the only kind we'd ever seen 'til recently) to see what happened to their bodies. Their bones weakened and their guts slowly shrank (oh, good).

It was only in 2022 that scientists finally discovered what really goes on -- females lay millions of eggs, which are then fertilised en masse by what I assume are very well-hydrated male eels.

We have yet to witness European eels mating in the wild, however.

Remember when we said sexually mature eels seem to deteriorate? That might be why they only grow genitals once they approach the Sargasso Sea.

Once they've laid their eggs, European eel larvae -- which bob around like tiny transparent leaves -- ride the currents for thousands of miles until landing on the shores of Eastern Europe.

There, they turn into bootlace-like creatures; after a while they migrate towards bodies of fresh water.

Only once they're old enough to breed do they become metre-long silver eels. That's their last life stage, but hey -- at least they have 20 to 30 years of pre-puberty to enjoy.