Essential oil ofLippia grata(Verbenaceae) is effective in the control of monogenean infections inColossoma macropomumgills, a large Serrasalmidae fish from Amazon

This study investigated the efficacy ofLippia grataessential oil (EO) against monogeneans ofColossoma macropomumand effects on the haematology after immersion baths. In the in vitro assays, the efficacy of 100, 250, 350 and 700 mg/L ofL. grataEO and two controls were tested, of which one control was with the cultivation tank water and the other was with the tank water and 70% ethyl alcohol. Composition of majority bioactive compounds in the EO was carvacrol (48.12%), p-cymene (24.39%) and gamma-terpinene (2.49%).Anacanthorus spathulatus,Notozothecium janauachensis,Mymarothecium boegeriandLinguadactyloides brinkmanniobtained of fish gills showed 100% immobilization in the in vitro assays when exposed to 700 and 350 mg/L after 30 min and 2 hr respectively. Fish showed tolerance to 700 mg/L of the EO, which was used in therapeutic in three consecutive baths, which caused lamellar hyperplasia inC. macropomumgills. The 700 mg/L of the EO in the therapeutic baths showed an efficacy of 95.1% against the monogeneans and caused decrease in haemoglobin, whereas control fish showed a reduction in mean corpuscular haemoglobin concentration. Results indicated that 700 mg/L ofL. grataEO is a safe and effective concentration to treatC. macropomuminfected with monogeneans.