This study investigated the in vitro efficacy of essential oils (OEs) of four species of plants of the family Piperaceae, these being; Piper hispidinervum, Piper hispidum, Piper marginatum and Piper callosum, in the control of Neoechinorhynchus buttnerae acanthocephalus that affect tambaqui. The tested concentrations of OE were: 0.19; 0.39; 0.78; 1.56; 3.125; 6.25; 12.5; 25 and 50 mg.mL-1, in triplicate, into p...