Tarragon (Artemisia dracunculus) Essential Oil at Optimized Dietary Levels Prompted Growth, Immunity, and Resistance to Enteric Red-Mouth Disease in the Rainbow Trout (Oncorhynchus mykiss)

Abstract

Fingerlings of the rainbow trout, Oncorhynchus mykiss (n = 300, 10.63 ± 0.6 g), were fed tarragon (Artemisia dracunculus) essential oil (TGO) for 2 months to examine its effects on growth properties, immunity, and resistance to Yersinia ruckeri infection. The treatments were control or TG1, TG2 (fed 0.5% TGO), TG3 (1% TGO), and TG4 (2% TGO). According to the results, an improvement was observed in growth parameters in all TGO-treated groups compared to the control ($P<0.05$). The digestive enzyme activities (protease and lipase) were significantly elevated in response to dietary TGO ($P<0.05$). The immune system of the fish was enhanced by TGO, as it stimulated the immune parameters in serum (lysozyme, myeloperoxidase (MPO), alternative complement (ACH50), Ig) and mucus (lysozyme, protease, ACH50, Ig) ($P<0.05$). The treatments, TG3 and TG4, showed more immune performance in response to TGO ($P<0.05$). The fish in TG2 treatment had a higher levels of serum total protein than other groups ($P<0.05$). The concentration of triglycerides (TRIG) and cholesterol (CHOL) in serum significantly decreased ($P<0.05$) in response to TGO, as the lowest levels were observed in the treatment, TG3. The antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) of serum elevated in TGO-treated fish, with the maximum values for the TG4 group ($P<0.05$). TGO reduced ($P<0.05$) alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels in serum. After bacterial challenge, the TGO-treated fish showed lower mortality compared to the control, where the lowest mortality was observed in TG4 ($P<0.05$). In conclusion, TGO improved growth, immunity, and survival after bacterial challenge in the rainbow trout, with more performance in fish fed 1%–2% TGO.