The anti-parasitic effect of Melaleuca alternifolia oil against gills monogeneans (Dactylogyrus spp) infestation of Clarias gariepinus: Hematology, immune response, and histopathological/immunohistochemical investigation of gills

Monogeneans induce significant economic losses and pose a danger to the sustainability of aquaculture. Using disinfectant medication has detrimental effects on fish health. Therefore, it is essential to look for efficient safe alternatives for the chemical medication. The present study exhibits that tea tree (Melaleuca alternifolia) essential oil (MAO) might provide a promising anti-parasitic alternative for conventional anthelmintics to treat gill monogeneans (Dactylogyrus spp) infestation in African catfish. The in vitro anthelmintic capability of different concentrations of MAO (10, 20, 30, and 40 mg/L) was tested for 8 h. An in vivo assay was applied for ten days, where fish (n = 200; 80.37 ± 5.98 g) were assigned at random into four groups in five replicates (10 fish/replicate), (control, MAO, Dactylogyrus spp, and MAO + Dactylogyrus spp). A concentration of 40 mg/L of MAO was used as a therapeutic dose. The outcomes of the in vitro assay demonstrated that the survival of Dactylogyrus spp was inversely correlated with the concentrations of MAO. In vivo, the parasitic intensity and vitality were significantly reduced by MAO bath treatment and inversely correlated with the time of exposure. Dactylogyrus spp infestation induced significant lowering (p < 0.05) in hematological and protein profiles (red and white blood cells, hemoglobin, packed cell volume %, total protein, albumin, and globulin) and immune-antioxidant responses (lysozyme, nitric oxide, complement 3, catalase, reduced glutathione, and total antioxidant capacity). Moreover, an apparent rise (p < 0.05) in the level of stress biomarkers (glucose and cortisol) was the consequence of Dactylogyrus spp infestation. Dactylogyrus spp-infested fish exhibited the highest mortality rate (48%) and marked histopathological changes in the gills (hyperplasia, inflammation, hemorrhages, and sloughing with inflammatory cells infiltrates) with an up-regulated apoptotic marker (caspase-3). Interestingly, treatment of Dactylogyrus spp-infested fish with MAO improved these biomarkers and decreased the mortality rate (18%) with an observable regeneration of the histopathological alterations. Overall, these findings suggest that MAO as an aqueous addition can protect fish from the harmful effects of Dactylogyrus spp and provide a promising anti-parasitic agent.