European eels are critically endangered and undertake one of the most extraordinary migrations in nature, yet face threats from barriers, parasites, and an aquaculture industry based entirely on wild-caught juveniles.
European eels have one of the most complex and welfare-significant life histories of any fish. Glass eels captured for aquaculture experience crowding stress during collection and transport. Aquaculture conditions for eels involve high stocking densities and artificial lighting to accelerate growth. Parasitic infections are endemic. The eel's extraordinary migration drive is entirely suppressed in captivity. Slaughter methods for market eels vary in their welfare properties. The wild population decline means every glass eel diverted to aquaculture reduces the wild breeding population. Conservation programs including passage restoration and glass eel restocking aim to support population recovery. The parasitic nematode Anguillicola crassus causes swim bladder damage affecting swimming ability in surviving eels.