Toxicity of the essential oil of Mentha piperita in Arapaima gigas (pirarucu) and antiparasitic effects on Dawestrema spp. (Monogenea)

This study evaluated the in vitro and in vivo effects of the essential oil of Mentha piperita on monogeneans and its toxicity for Arapaima gigas. For the in vitro assay, gills of A. gigas naturally infected by Dawestrema cycloancistrium and Dawestrema cycloancistrioides were exposed to 0, 80, 160 and 320mgL−1 of M. piperita, which demonstrated anti-helminthic activity. In the toxicity test, A. gigas fingerlings were exposed to 0, 20, 40, 80, 100, 130 and 160mgL−1 of M. piperita to determine the lethal concentration (LC50-4h), which was found to be 38mg/L. Fish that had been exposed to 80, 100, 130 and 160mgL−1 presented epithelial elevations, fusion of the secondary lamellae, hypertrophy and aneurism. Necrosis was only observed at a concentration of 160mgL−1 of M. piperita. The in vitro results demonstrated that the anti-helminthic activity of M. piperita against Dawestrema spp. was dose dependent. However, baths with 40mgL−1 of essential oil of M. piperita were not effective against monogeneans in the gills of A. gigas. Therefore, since this anti-parasitic substance was in vitro effective and the concentrations used in the baths were not efficient and caused tissue alterations in the gills of the fish, other therapeutic strategies should be tested in order to increase the efficacy of this phytotherapeutic substance and reduce its toxicity for A. gigas. Finally, this study investigated the efficacy of M. piperita essential oil against parasites of A. gigas, for the first time. This manuscript represents original article on the in vitro and in vivo effects of the essential oil of Mentha piperita on monogenoideans and its toxicity for Arapaima gigas, the giant fish from Amazon. Thus, this study investigated the efficacy of M. piperita essential oil against these parasites of A. gigas, for the first time •The exact limits/doses (mg L-1) concerning the toxicity and LC50-4h need to be added.•Toxicity of the Mentha piperita essential oil and their influence on the histopathology of for Arapaima gigas.•Anti-helminthic activity of the essential oil of M. piperita against monogeneans of Arapaima gigas is dose-dependent.•Mentha piperita killed the parasites after 30 min in the in vitro trial.•Parasites exposed to water died after 9 h in the in vitro immobilization test.