Introduced catfish now dominate Spanish rivers, endangering native wildlife

A German angler released thousands of juvenile Wels catfish into Spain's Ebro River in 1974, and five decades later the invasive predator threatens native species across the basin.

In 1974 German biologist and recreational fisherman Roland Lorkowsky introduced thousands of young Wels catfish into Spain's Ebro River to establish a world-class sport fishery. The species, Europe’s largest freshwater predator, can grow beyond 9 feet and 440 pounds, feeding on fish, amphibians, birds and small mammals. Over fifty years it has spread throughout the Ebro basin and other Spanish rivers, forming self-sustaining populations that now target endangered migratory species such as Allis shad and Atlantic salmon.

Zoology professor Carlos Fernández Delgado calls the catfish an “ecological time bomb” because native ecosystems lack defenses against such a large predator, and Spanish law now prohibits its release, yet removal is considered virtually impossible. Climate-induced warming may enable further expansion northward, with evidence of colonisation in Belgium and the Netherlands. Despite the ecological threat, a thriving catch-and-release angling industry in Spain and Italy reduces governmental appetite for eradication.