In 1974, a German fisherman released thousands of baby catfish into a Spanish river; 50 years later they are threatening native wildlife as an 'ecological time bomb'

German biologist and recreational fisherman Roland Lorkowsky released thousands of juvenile Wels catfish into Spain's Ebro River in 1974. His goal was simple and positive: to create a world-class sport fishery by introducing one of Europe's biggest freshwater fish.

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