In 1974, a German fisherman released thousands of baby catfish into a river; 50 years later, they rule the waters
One man’s decision to introduce a large freshwater predator into a river has reshaped an entire ecosystem. Half a century later, the giant fish continues to spread, threatening native wildlife while attracting anglers from around the world.
Exactly 50 years ago, in 1974, German biologist and recreational fisherman Roland Lorkowsky released thousands of juvenile Wels catfish (Silurus glanis) into Spain’s Mequinenza Reservoir on the Ebro River. His goal was simple: create a world-class sport fishery by introducing one of Europe’s biggest freshwater fish.
Few could have predicted the long-term consequences.
Today, the Wels catfish has become one of the dominant predators in many Spanish waterways. Conservationists describe it as an ecological threat, while sport fishermen see it as the ultimate trophy catch.
Earlier this year, anglers Abel Monreal, Fernando Equiza, Santiago Ramírez and Óscar Gómara landed one of the largest Wels catfish ever caught in Spain. The fish measured more than 9 feet long (2.81 meters) and weighed about 287 pounds (130 kilograms) after being caught in the Ebro River near Buñuel, in northern Spain.
Europe’s freshwater giant
The Wels catfish is the largest freshwater fish native to Europe. It can grow to more than 8 feet (2.5 meters) in length, with exceptional individuals reportedly exceeding 9 feet and weighing more than 440 pounds (200 kilograms). Its enormous size, long lifespan and ability to thrive in a wide range of habitats have made it one of the continent’s most successful freshwater predators.
The species is an opportunistic feeder, consuming almost anything it can swallow. Its diet includes fish, crayfish, frogs, water birds and even small mammals that venture too close to the water’s edge. Adult fish are estimated to consume around 5% of their body weight every day.
Over the past five decades, the Wels catfish has spread throughout much of the Ebro basin and into other Spanish rivers and reservoirs, establishing self-sustaining populations that wildlife managers now consider virtually impossible to eliminate.
Carlos Fernández Delgado, a zoology professor at the University of Córdoba, has described the species as an “ecological time bomb” because native freshwater ecosystems did not evolve alongside a predator of this size.
A familiar invasive story for Americans
While the Wels catfish has not established wild populations in the United States, Americans have experienced similar ecological problems with other introduced fish.
Perhaps the best-known example is invasive carp. Several species were imported into the United States during the 1970s for aquaculture and wastewater treatment before escaping into the Mississippi River system during floods. Decades later, they have spread across much of the country’s largest river network, competing with native fish for food and habitat and proving extraordinarily difficult to control. Federal agencies now consider them one of the biggest threats to U.S. freshwater ecosystems.
Another notorious example is the northern snakehead, a predatory fish native to Asia that was illegally released into U.S. waters. After reproducing successfully, it established populations in several states and became one of America’s most closely watched invasive species.
A lasting ecological legacy
For Spanish conservationists, the Wels catfish remains one of the country’s most damaging invasive freshwater species. Native fish evolved without a predator capable of reaching such enormous size, leaving many vulnerable to predation alongside existing pressures such as pollution and habitat loss.
Although Spanish law prohibits releasing or transporting the species, experts say eradication is no longer realistic. Its size, rapid reproduction and the complexity of river systems make complete removal virtually impossible.
Fifty years after one bucket of juvenile fish was emptied into a reservoir, the Wels catfish continues to dominate the waters where it was never supposed to exist.
Get closer to the game! Whether you like your soccer of the European variety or that on this side of the pond, our AS USA app has it all. Dive into live coverage, expert insights, breaking news, exclusive videos, and more. Plus, stay updated on NFL, NBA and all other big sports stories as well as the latest in current affairs and entertainment. Download now for all-access coverage, right at your fingertips – anytime, anywhere.
And there’s more: check out our TikTok and Instagram reels for bite-sized visual takes on all the biggest soccer news and insights.