The European eel (Anguilla anguilla) has declined by over 90% since the 1980s, making it critically endangered. Welfare concerns intersect with conservation: glass eel (juvenile) harvesting for aquaculture stocking involves intensive handling, transport stress, and high mortality rates. European eel aquaculture maintains eels at high densities in recirculating systems throughout 2-4 year production cycles. Eels are highly sensitive to water quality fluctuations; ammonia and dissolved oxygen variations cause acute stress responses. Slaughter methods for farmed eels vary widely: live immersion in ice water (causes prolonged distress), electrical stunning, and spiking are used without standardised welfare protocols. Wild eel migration faces barriers from hydropower turbines causing lethal injury. Conservation-welfare tensions arise in stocking programmes - hatchery-reared eels are unavailable (the full life cycle has never been closed in captivity), requiring wild-caught glass eels for aquaculture stocking. CITES Appendix II listing restricts international glass eel trade.