Prochilodus lineatus has been considered an ecosystem engineer in the Neotropics given its infl uence on important ecosystem processes, and it is therefore relevant to understand their inter-specifi c relationships. The association of P. lineatus with parasitic helminths was studied in two isolated shallow lakes of the alluvial plain of the Middle Paraná River. Only two species of gastrointestinal nematodes were found:Spinitectus asperus (Cystidicolidae) and Klossinemella iheringi (Atractidae), with S. asperus having higher prevalence and mean intensity values. This is the fi rst record of K. iheringi in the Middle Paraná River, Argentina, as well as the southernmost citation of S. asperus.