In vitro efficacy of two terpenes against ancyrocephalid monogeneans from Nile tilapia

Terpenes are naturally produced compounds with a broad range of biological activities. Currently, there is limited information regarding the anthelminthic effect of terpenes against monogenean parasites of fish. The aim of this work was to evaluate the in vitro efficacy of two terpenes [α-terpinene and (+)-limonene oxide] against ancyrocephalid monogeneans found on farmed Nile tilapia (Oreochromis niloticus). (+)-Limonene oxide was more effective in killing these parasites than α-terpinene, with 86 and 90% mortality at concentrations of 36 and 55.4 mg/L, respectively, with a 5-h treatment. The estimated 5-h EC₅₀ of (+)-limonene oxide was 4.8 mg/L. Even though this compound has the potential to be used as an anthelmintic compound in finfish aquaculture, before in vivo experiments are performed, additional studies are needed to find a more effective concentration, as well as to evaluate other terpenic compounds.