Effects of Herbal Extracts on Growth and Immune Response of Rainbow Trout (Oncorhynchus mykiss)

In this work, we assessed the impacts of aqueous methanolic extracts of laurel (Laurus nobilis) leaves (D), black mustard (Brassica nigra) seed (SH) and fenugreek (Trigonella foenum-graecum L.) seed (C) seeds on growth related parameters, immune parameters, cytokine gene expression, and bacterial infection resistance in rainbow trout (Oncorhynchus mykiss). Experimental diets containing each extract at 0.1, 1, or 5 g/kg-1 were administered to fish for 45 days, alongside a control diet. Growth, NBT activity, lysozyme, myeloperoxidase, and expression of TGF-β, IFN-1, TNF-α and IL-1β were assessed every 15 days. After feeding, fish were exposed to Yersinia ruckeri, Aeromonas salmonicida and Vibrio anguillarum. No statistically significant differences were observed in growth parameters among the groups (P > 0.05). The highest NBT activity occurred in D5 on day 15 and SH5 on day 30 (P<0.05). No alteration in lysozyme activity was observed, while myeloperoxidase exhibited higher values in SH1 on day 15 (P<0.05). Gene expression varied significantly (P<0.05). Fenugreek at 1 and 5 g/kg-1 enhanced immune responses and survival, especially against Aeromonas salmonicida and Vibrio anguillarum.