Antiparasitic activity of the essential oil of Lippia alba on ectoparasites of Colossoma macropomum (tambaqui) and its physiological and histopathological effects

This study investigated the in vivo and in vitro antiparasitic effects of the essential oil of Lippia alba and the blood-related and histopathological alterations that it causes in Colossoma macropomum. In the in vitro trial, the anthelminthic effects of 160, 320, 640, 1280 and 2560mg/L of the essential oil were tested against monogenoideans (Anacanthorus spathulatus, Notozothecium janauachensis and Mymarothecium boegeri) of the gills of this fish, which are its natural parasites. The concentrations of 1280mg/L and 2560mg/L showed 100% efficacy after 20min of exposure to the essential oil, while at lower concentrations this efficacy against the gill monogenoideans only occurred after 2–3h of in vitro exposure. However, in the controls, mortality of all of these monogenoideans only occurred after 9h. A total of 240 fry were distributed into four treatments (20 fish per repetition) and three repetitions were used in the in vivo trial for baths with 100 and 150mg/L of the essential oil of L. alba, for 30min. The efficacy in this trial against Ichthyophthirius multifiliis in fish exposed to 100 and 150mg/L of the essential oil was 40.7% and 50.3%, respectively. However, for monogenoideans, there was efficacy of 14.0% only in the fish exposed to 100mg/L of the essential oil used. Moreover, the fish exposed to these concentrations of the essential oil presented increased plasma glucose levels, thus denoting signs of stress. Severe lesions such as hyperplasia, fusion of the lamellar epithelium, capillary dilatation, epithelial detachment, lamellar aneurysm, epithelial rupture with hemorrhage, congestion, edema, necrosis, mucous cell proliferation, chloride cells and lamellar hypertrophy were observed in the gills of the fish exposed to 100 and 150mg/L of the essential oil of L. alba. Alterations to total protein levels, hemoglobin, hematocrit, red blood cell number, thrombocytes number, white blood cell number, lymphocytes, eosinophils and blood neutrophil number was also observed in these fish. The essential oil of L. alba showed great potential for antiparasitic treatment, given that it had high in vitro efficacy against monogenoideans and in vivo efficacy against the protozoon I. multifiliis. Because of the low concentrations of the essential oil (100 and 150mg/L) that were tolerated by the fish and thus could be used in the therapeutic baths, the efficacy against monogenoideans was low. This indicates that there is a need for additional strategies for using this essential oil in antiparasitic treatments, since the concentrations that eliminate these ectoparasites are toxic for the hosts. Lastly, this was the first study on the antiparasitic activity of L. alba.The manuscript entitled “Antiparasitic activity of the essential oil of Lippia alba on ectoparasites of Colossoma macropomum (tambaqui) and its physiological and histopathological effects”, represents original article on use of the essential oil of Lippia alba on ectoparasites of tambaqui, an important finfish of Amazon region. This manuscript includes treatment in vitro against monogeneans, and in vivo against protozoans and monogeneans, besides histopathological and hematological features of the fish exposed to different concentrations of L. alba, a medical plant from South and Central America.