Effects of Red Kojic Rice Supplementation on Growth, Immunity, Antioxidant Capacity, and Intestinal Health of Litopenaeus vannamei Fed a Diet with Fish Meal Replacement by Soybean Meal

This study aimed to investigate the effects of adding Red kojic rice (RKR) on the growth performance, digestive enzyme activity, non-specific immunity, antioxidant capacity, and intestinal health of Litopenaeus vannamei fed a diet with fishmeal replacement by soybean meal. Shrimps (initial mean weight = 1.88 ± 0.03 g) were fed six experimental diets for 8 weeks, including a normal fishmeal control group (FM), a soybean meal-replaced fishmeal group (H0), and four soybean meal-replaced fishmeal groups supplemented with 0.5%, 1%, 2%, and 4% RKR, respectively, which are designated as H1, H2, H3, and H4, respectively. Each group had three replicates, with 30 shrimp per replicate. The results showed that the final average weight (FWG), weight gain rate (WG), and specific growth rate (SGR) of H2 group were significantly higher than those of H0, H3, and H4 groups (p < 0.05). The feed conversion ratio (FCR) of H2 group was significantly lower than that of H0 and H4 groups (p < 0.05). In contrast to the H0 group, the blood ACP activity in the H2 group was significantly increased (p < 0.05). The blood lysozyme (LYZ) activity in H3 group was significantly higher than that in H1 group (p < 0.05), while the opposite was true for phenoloxidase (PO). The activities of trypsin and amylase in hepatopancreas of H3 group were significantly higher than those of H0 and H1 groups (p < 0.05). Compared with the FM group, the hepatopancreatic malondialdehyde (MDA) levels in H0, H3, and H4 groups were significantly increased (p < 0.05). Compared with the H0 group, the hepatopancreatic MDA levels in H1 and H2 groups were significantly decreased (p < 0.05). Analysis of gene expression levels in hepatopancreas revealed that antioxidant (gpx, sod, cat, gst, nrf2, trx, and ho-1), non-specific immune (tnf-α, il-1β, and ifn-γ), and digestive (trypsin and α-amylase) genes were suppressed in the H0 group but enhanced by RKR supplementation. Similar expression patterns of those genes were observed in the intestine. Microbial community analysis showed reduced diversity and altered composition in the H0 group, which were partially restored by RKR. Network analysis showed “small-world” property in microbial co-occurrence network. Metabolomic analysis revealed that among the differential metabolites, Bismurrayaquinone A and Harmol exhibit highly significant differences. Correlation analysis revealed that beneficial bacteria Rhodococcus_C and Oceanobacillus in H2 group exhibited higher richness and showed significant correlation. In conclusion, supplementation of 0.5–2% RKR promoted the growth performance, digestive enzyme activity, non-specific immunity, antioxidant capacity, and intestinal health of shrimp fed a diet with fishmeal replacement by soybean meal. The optimal RKR supplementing content is 1%.