The mysterious life cycle of the European eel remains a puzzle for modern science

Nature · Published 3 October 2026 Swipe more like this →

In short: For centuries, the European eel's origins were a complete mystery. Despite being a staple of global sushi markets, mating in the wild has never been observed. Today, this critically endangered species faces a precarious future, as human attempts to breed them in captivity have yet to complete their full life cycle.

The European eel (Anguilla anguilla) undergoes a complex, five-stage development process: larva, glass eel, elver, yellow eel, and silver eel. Unlike many migratory fish, these eels begin their lives in the ocean, specifically the Sargasso Sea, before migrating to fresh or brackish inland waters. After spending 5 to 20 years maturing, they undergo a transformation into the silver eel phase, marked by enlarged eyes and physiological changes driven by cortisol and 11-Ketotestosterone, which prepare them for their final journey back to the Sargasso Sea to spawn and die.

The species is currently classified as critically endangered, with population numbers estimated to have declined by 90% to 98% since the 1970s. This collapse is attributed to a combination of overfishing, habitat fragmentation caused by hydroelectric dams, and the spread of parasites like Anguillicola crassus. Pollution from polychlorinated biphenyls (PCBs) and natural shifts in the North Atlantic oscillation are also suspected contributors. Because the entire aquaculture industry relies on harvesting wild glass eels, the current trade remains inherently unsustainable.

Scientific efforts to save the species have focused on captive breeding, a notoriously difficult task. While researchers at DTU Aqua and the PRO-EEL project have made significant strides—extending larval survival from a few days in 2006 to around 140 days by 2022—the complete life cycle has not yet been replicated in a laboratory setting. This dependence on wild populations makes the European eel uniquely vulnerable, as conservationists and international bodies like CITES struggle to implement effective traceability and protection measures to reverse the decline of this ancient, elusive fish.

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