Eels are a much-loved delicacy in Japan, where remains found in tombs show they have been eaten there for thousands of years. But the animals are now so endangered that they command eyewatering prices and the attention of international traffickers. Despite its enduring popularity, much about the eel remains a mystery. Precisely how it reproduces is unclear, and coaxing it to do so in captivity without intervention has proved unsuccessful so far. IMAGES AND SOUNDBITES