I ended up studying European Eels a lot recently and my mind was blown by how prolific they are, and how culturally and historically important they are, and yet how little we know about them. My favourite one is that we’ve known they reproduce in the Sargasso Sea since the early 20th century, due to finding larvae there, but their breeding has never been observed in the wild, and up until February THIS YEAR, an adult European Eel had never been observed to be arriving at the sea. This has now been achieved with satellite tagging https://www.nature.com/articles/s41598-022-19248-8