Porphyra yezoensis polysaccharides enhance growth performance and antioxidant capacity in Sebastes schlegelii by improving gut microbiota and tissue morphology

Porphyra yezoensis polysaccharides (PPs), a traditional herbal extract, exhibit a wide range of biological activities, including antioxidant effects and the promotion of intestinal health. However, their impact on Sebastes schlegelii remains largely unknown. To address this gap, this study investigated the effects of dietary PPs supplementation (0, 4, 8, 12, and 16 g/kg) on growth performance, non-specific immunity, and intestinal health in juvenile S. schlegelii . Compared with the control group, fish fed diets containing 8, 12, and 16 g/kg PPs showed significantly higher weight gain ( P < 0.05). All treatment groups, except the control group, exhibited normal intestinal morphology. The 12 g/kg PPs group exhibited a significant increase in villus length and a decrease in goblet cell number ( P < 0.05). Increased populations of Clostridia and Bacillus , along with a reduction in Pseudomonadota , were observed, and microbial diversity was significantly enhanced in the 12 g/kg PPs group ( P < 0.05). Digestive enzyme activities, including amylase, lipase, and trypsin, were significantly higher in the 8 and 12 g/kg groups ( P < 0.05). The 12 g/kg group also showed increased activities of alkaline phosphatase, acid phosphatase, and lysozyme ( P < 0.05). Furthermore, intestinal expression of interleukin-6 ( IL-6 ) , tumor necrosis factor-alpha ( TNF-α ), and zonula occludens-1 ( ZO-1 ) was significantly upregulated ( P < 0.05). Antioxidant enzyme activities, including total superoxide dismutase and total antioxidant capacity, were significantly enhanced in the 8, 12, and 16 g/kg groups ( P < 0.05). Quadratic regression analysis indicated an optimal dietary PPs supplementation level of 13.65 g/kg. Our findings provide theoretical support for the use of PPs as a dietary additive in aquaculture. • Porphyra yezoensis Polysaccharides (PPs) could increase the expression of ZO-1 gene in the intestinal tract of S. schlegeli . • PPs at different concentrations improved the intestinal flora of S. schlegeli and increased the proportion of beneficial bacteria. • PPs could improve the activities of liver antioxidant enzymes and intestinal digestive enzymes of S. schlegeli .