What is the name for a young eel?

An elver - the stage after the transparent glass eel, when it has begun to pigment and is migrating up rivers. The full sequence is remarkable: leptocephalus larva, glass eel, elver, yellow eel for anything up to twenty years in fresh water, then silver eel for the return to the sea.

Elvers are also one of the most valuable wildlife products in the world by weight. European eels cannot be bred in captivity - nobody has closed the life cycle - so every farmed eel starts as a wild-caught juvenile, and demand from East Asian aquaculture has driven prices to thousands of pounds a kilogram at times. That has produced large-scale smuggling: elvers are trafficked out of Europe in suitcases of water in an illegal trade that Europol has compared in value to some drug routes.

The species is critically endangered, with recruitment down well over ninety per cent since the 1980s. Trade in European eels was banned outside the EU in 2010 and the smuggling continued. The animal that nobody could explain for two thousand years - Aristotle thought they arose from mud, Freud spent months dissecting them looking for gonads - is now disappearing before the basic biology has been finished.