Differential Effects of Lycium Barbarum Polysaccharides and Seaweed Polysaccharides on Growth, Immunity, and Hepatic Lipid Metabolism in Juvenile Rainbow Trout (Oncorhynchus mykiss)

Polysaccharides play crucial roles in medicine and nutrition, serving as dietary additives that help maintain fish health. This study systematically evaluated the effects of dietary supplementation with plant-derived Lycium barbarum polysaccharides (LBP) and Seaweed-derived polysaccharides (SPs) on growth, metabolism, and immune function in rainbow trout (Oncorhynchus mykiss). A total of 270 juvenile rainbow trout (15.50 ± 0.71 g) were randomly divided into three groups (control group, CG; 1.5 g/kg LBP; 1.5 g/kg SPs), with 90 fish in each group. The feeding trial lasted 56 days, with sampling at days 28 and 56. Compared with CG, SPs increased WGR by approximately 39.4%, decreased FCR by approximately 44.7%, and elevated muscle Ala, Glu, and Gly contents. SPs also improved intestinal microbiota balance and promoted the synthesis of amino acids and short-chain fatty acids (SCFAs). In addition, SPs significantly enhanced CAT and SOD activities and upregulated IL-10 expression by approximately 2.3-fold. Compared with the CG, LBP can reduce the total cholesterol content by 33.3%, inhibit lipid synthesis, and promote fatty acid oxidation. It also upregulates the expression of the PPARα gene by approximately 2.4-fold. In the Aeromonas salmonicida challenge test, survival rates of the SPs and LBP groups were 30% and 20% higher, respectively, than that of CG. These results indicate that SPs were more effective in promoting growth and enhancing immunity, whereas LBP showed superior performance in metabolic regulation. This study provides a basis for the targeted application of these two substances.