In 1974, a German fisherman released thousands of baby catfish into a river; 50 years later they are threatening native wildlife

In 1974, German biologist Roland Lorkowsky introduced the Wels catfish to Spain's Ebro River, where they've since become a top predator, threatening native wildlife. Their large size and aggressive feeding present significant hurdles for conservationists trying to maintain balance. Worsening climate change conditions could facilitate their further invasion into European waters, leading experts to deem eradication efforts nearly impossible.