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 320 mg•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 160 mg•L −1 were 100% effective against these parasites within 20 and 60 min of exposure, respectively. The 80 mg•L −1 concentration was approximately 80% effective with 3 h of exposure, reaching 100% with 6 h of exposure. The 40 mg•L −1 concentration was also 100% effective with 6 h of exposure. The other concentrations were only weakly effective in vitro. Parasite mortality in controls (water or water + alcohol) began after 3 h, with 100% mortality after 8 h. In vivo tests, in which fry of C. macropomum were placed in baths with 20 mg•L −1 of the essential oil for 60 min, and 40 mg•L −1 for 30 min, 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 24 h after the treatments were applied, with no difference between treatments. Histological changes observed in the gills after exposure to concentrations of 20 and 40 mg•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 40 mg•L −1) was not effective. Statement of relevance: The 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.

Abstract:Freshwater sponges are abundant in the Amazon region and they have been known to cause dermatitis (acute inflammation) since the beginning of the 20 th century. To determine whether additional constituents, besides their body spicules, cause dermatological reactions in humans, an experimental study was developed and carried out using mice and Drulia uruguayensis prepared in three different forms: intact sponges (IS), macerated sponges (MS) or isolated spicules -megascleres (ISM). The cells most commonly involved in inflammatory reactions (mast cells, eosinophils and neutrophils), as well as intraepithelial lymphocytes and degranulated mast cells, were counted so that they could be used as parameters to determine which of the sponge preparations induced the greatest reaction. The effects of the sponge on the skin were then determined by histological analysis. The results obtained showed that IS caused the greatest inflammatory reaction (p = 0.000005), activating mainly mast cells (p = 0.0018). The histopathological analysis revealed a slight loss of continuity of the epidermis when ISM or IS were applied. These findings allow us to conclude that a structurally intact sponge can cause a greater inflammatory reaction in the first contact because of its ability to perforate the skin and allow inflammatory agents to enter. Other proteins present in dried sponge bodies could induce allergic but not toxic responses (in contact with the entire sponge, a large number of pharmacologically inert proteins may be introduced, with a potential allergen).