Prepare to be baffled by what we don't know about eels

More than a century ago, all that people knew about European eels was that they lived in the rivers and streams for decades — until they swam out to the ocean and never returned. Eventually, tiny eels would show up and the cycle would start again. Where did the adult eels go? Where did the baby eels come from? Did they even reproduce at all or just spontaneo…