Assessing the effects of Rheum ribes extract on growth, immunity, antioxidant response, and gene expression in triploid rainbow trout (Viviers Strain) under river conditions

This research aimed to examine the impact of Rheum ribes (RRE) on growth performance, immune function, antioxidant activity, and gene expression in triploid rainbow trout reared in river conditions. For eight weeks, the fish were given diets that included different levels of RRE extract, ranging from no supplement at all to incremental additions of 0.5 %, 1 %, 1.5 %, 2 %, 2.5 %, and up to 3 %. Growth criteria such as weight gain, final weight (RRE 1–3 %), specific growth rate, and weight gain percentage (RRE 2 %) were significantly elevated, and the feed conversion ratio in the RRE2 % was significantly decreased against the control (Ctrl) group (P < 0.05). Hematological parameters, except for white blood cells (RRE 1.5 and 2 %), were not significant compared to the Ctrl group (P > 0.05). Serum biochemical parameters were not significantly different at any RRE doses compared to the Ctrl group (P > 0.05). Unlike other biochemical parameters, cortisol and glucose were significantly increased in all groups receiving RRE, except the group receiving 0.5 % RRE, compared to the control group (P < 0.05). Serum catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) levels significantly increased at RRE doses 1–3, while serum malondialdehyde significantly decreased in these groups compared to the Ctrl (P < 0.05). Immune parameters such as total immunoglobulin (RRE 1–2 %), lysozyme (RRE 0.5–2 % and 3 %), complement 3 (RRE 2–3 %), protease (RRE 0.5 %, 2 %, and 3 %), nitroblue tetrazolium (all RRE levels), and serum bactericidal activity against Streptococcus iniae (RRE 2 %) were significantly increased versus the Ctrl group (P < 0.05). Digestive enzymes such as trypsin (RRE 1.5–3 %), alpha-amylase (RRE 1–3 %), and lipase (RRE 1.5–2.5 %) showed a notable elevate against the Ctrl group (P < 0.05). The expression of antioxidant genes, including Nuclear factor erythroid 2-related factor 2 (Nrf2), CAT, SOD, GPx, and glutathione reductase, was upregulated at all RRE levels against the Ctrl group (P < 0.05). Other genes, such as tumor necrosis factor-alpha (TNF-α) and insulin-like growth factor 1 (IGF-1), were upregulated at RRE levels of 1.5–3 %, while the interleukin-8 gene was upregulated at all RRE levels, and interleukin-1 beta was upregulated at RRE levels of 1 %, 2 %, and 3 % in relation to the Ctrl group (P < 0.05). In general, it can be concluded that the 2 % dose of RRE is the optimal level, showing a significantly greater effect on growth, immune response, antioxidant activity, digestive enzymes, and immune-antioxidant genes expression in rainbow trout relative to the other doses.