Effects of Sophora flavescens ethanol extract supplementation in high soybean meal diets on growth, intestinal antioxidant status and immune response in Pearl Gentian grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂)

This study evaluated the effects of adding Sophora flavescens ethanol extract to high soybean meal feed (soybean meal replaced 50% fish meal protein) on growth, antioxidant status, and immune response in pearl gentian grouper. The fish (72.5 ± 0.5 g) were randomly divided into three groups: the fish meal group (the FM group), the soybean meal group (the SBM group), and the SBM + 0.2% S. flavescens ethanol extract group (the SBMSF group). Three groups of iso-nitrogenous (50% protein) and iso-lipidic (10% lipid) diets were prepared and fed to fish for 8 weeks. The weight gain rate of the SBM group was 47.53 ± 13.07%, which was significantly decreased compared with the FM group (P < 0.05). After adding ethanol extract of S. flavescens, the average weight gain rate of the SBMSF group recovered to 89.75 ± 30.16%. Compared to the FM group, the SBM group showed decreased contents of immunoglobulin M (IgM) and complement 3 (C3) in serum and increased activity of trypsin in the intestinal tract, and the above phenomenon was effectively reversed in the SBMSF group. Intestinal antioxidant enzymes activity, including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX), were significantly higher in the SBMSF group and FM group, than the SBM group (P < 0.05). The SBMSF group also had lower levels of malondialdehyde (MDA) than the SBM group. The SBM group showed increased intestinal inflammatory cytokine (tnf-α, il-8, il1-β) mRNA expression and decreased anti-inflammatory il-10 expression compared to the FM group, but the SBMSF group showed a reversal of these expression changes. Histological analysis revealed shortened intestinal villus folds, wider lamina propria, more goblet cells, and higher inflammatory cell infiltration in the SBM group versus the FM group, with the SBMSF group significantly improving these intestinal health parameters. In summary, S. flavescens ethanol extract supplementation in high-SBM feed enhanced antioxidant status, immunity, and growth in pearl gentian grouper, and exerted anti-inflammatory and antioxidant benefits. This highlights implications for developing soybean meal aquafeeds and therapies.