Background: Lernaea cyprinacea was introduced in South America with cyprinids. To the best of our knowledge, this ectoparasite has not been reported in Santa Fe province (Argentina). Objective: To report Lernaea cyprinacea presence in Rhamdia quelen under hatchery conditions in Santa Fe province (Argentina). Methods: In May 2014, samples of L. cyprinacea attached to the fins and flanks of R. quelen were obtained in the Chronobiology Laboratory of the Veterinary Sciences School at Esperanza (Santa Fe, Argentina) where they were collected and identified. Results: A description of L. cyprinacea is presented along with detailed records previously reported in this and other regions. Conclusions: Presence of this parasite constitutes evidence of the introduction of exotic species through commercialization of their natural hosts and the potential pathogen colonization of natural environments, which constitutes a threat to the integrity of aquatic ecosystems.