Eel aquaculture — particularly of European and Japanese eel — involves severe overcrowding, capture of wild juveniles, and no effective welfare regulation in most countries.
Eel welfare is poorly understood and almost entirely unregulated. At extreme stocking densities, eels experience chronic stress with persistently elevated cortisol and suppressed immune function. Disease outbreaks are common and often treated with antimicrobials applied to entire ponds. Eels exhibit high aggression at density, causing injuries particularly to fins and skin. Slaughter methods — including chilling in ice slurry while conscious — are among the most welfare-poor of any commercially farmed species. The removal of millions of wild glass eels annually from critically depleted rivers compounds the ecological harm, threatening wild population recovery while also raising questions about the welfare of wild-caught animals.