We describe the infestation of the Prochilodus magdalenae fingerlings by anchor worm ( Lernaea cyprinacea ). In a group of fish grown in the Aquaculture Laboratory of the University of Magdalena it was register a high mortality (50/50 number of fish / number of deaths) in small fish that had numerous white spots on the body, visible through skin. By histology of the lesions we identified copepod parasite that affects striated muscle, where it is surrounded by chronic inflammation. The high mortality is directly related to parasite infestation mainly concentrated on the body surface of the animals.