Antiparasitic, physiological and histological effects of the essential oil of Lippia origanoides (Verbenaceae) in native freshwater fish Colossoma macropomum

Abstract

This study examined the in vitro and in vivo, histopathological, anti-parasitic and hematopathological effects of the essential oil of Lippia origanoides on Colossoma macropomum. Essential oil concentrations of 10, 20, 40, 80, 160 and 320mg·L−1 were tested in vitro against monogenoideans (Anacanthorus spathulatus, Notozothecium janauachensis and Mymarothecium boegeri) from the gills of C. macropomum. Concentrations of 320 and 160mg·L−1 were 100% effective against these parasites within 20 and 60min of exposure, respectively. The 80mg·L−1 concentration was approximately 80% effective with 3h of exposure, reaching 100% with 6h of exposure. The 40mg·L−1 concentration was also 100% effective with 6h of exposure. The other concentrations were only weakly effective in vitro. Parasite mortality in controls (water or water+alcohol) began after 3h, with 100% mortality after 8h. In vivo tests, in which fry of C. macropomum were placed in baths with 20mg·L−1 of the essential oil for 60min, and 40mg·L−1 for 30min, did not lead to reductions in parasite abundances. In addition, the essential oil had an anaesthetic effect on fish, increased total protein levels, increased monocyte and neutrophil numbers, and reduced haematocrit. Slight to moderate and severe damage was observed in the gills of C. macropomum fingerling immediately after exposure to the essential oil, and 24h after the treatments were applied, with no difference between treatments. Histological changes observed in the gills after exposure to concentrations of 20 and 40mg·L−1 of L. origanoides essential oil were: hyperplasia and fusion of the lamellar epithelium, capillary dilation, displacement of the lamellar epithelium, and lamellar aneurism and epithelial rupturing with haemorrhaging. Oedema, mucous and chloride cell proliferation, lamellar hypertrophy, congestion and necrosis were less frequently observed. It can be concluded that the essential oil of L. origanoides was dose-dependent in vitro effect against monogenoidean parasites of C. macropomum. Unfortunately, the low concentrations tolerated by the fish in the vivo assay (20 and 40mg·L−1) was not effective. Statement of relevanceThe manuscript represents original research on use of the essential oil of Lippia origanoides against ectoparasites of Colossoma macropomum, an important finfish of Amazon region. This manuscript includes treatment in vitro against monogenoideans, and in vivo against protozoans and monogenoideans. Besides, histopathological and hematological analysis of the fish exposed to different concentrations of L. origanoides, a medical plant from North, Central and South America, were performed.