Effects of -derived brown algae polysaccharide (UPS) on the nutritional composition, digestive capacity, immune performance and intestinal microbiota of juvenile sea cucumber ().

Background: Brown algae polysaccharides (BAPs), derived from marine brown algae, represent bioactive macromolecules with potential functional feed applications as novel feed additives for improving the health and nutritional quality of aquatic animals. Previous studies have shown that BAPs possess antioxidant, anti-inflammatory, immunomodulatory, antimicrobial, and antiviral activities. BAPs extracted from (UPS) contain kinds of BAPs such as alginate, mannitol, fucoidan and fucoheterosaccharides but there are few studies on the combined effects of these BAPs.

Methods: This study investigated the effects of UPS by supplementing juvenile sea cucumbers with 0%, 0.5%, 1%, 1.5%, 2%, and 3% UPS (polysaccharide/sea cucumber biomass, W/W). After 60 days feeding, the nutritional composition of body wall, digestive capacity and immune performance were analyzed. The diversity of intestinal microbiota in sea cucumber was analyzed using 16S rRNA gene sequence amplification technology to elucidate the effects of UPS supplementation on the composition and function of intestinal microorganisms.

Results: It was demonstrated that UPS supplementation significantly increased the nutritional content of the juvenile sea cucumber body wall although growth performance remained unchanged. The polysaccharide content peaked at 1% supplementation of UPS, which was 1.6-fold higher than that of the control group. Moreover, UPS also enhanced intestinal digestive enzyme activity such as cellulase or lipase activity, which was maximized at 1% or 3% supplementation with 5.8-fold and 1.6-fold higher than that of the control group. Additionally, UPS could improve immune performance of juvenile sea cucumber by significantly elevating superoxide dismutase activity (T-SOD). It was worth noting that low UPS concentrations (1% and 1.5%) reduced malondialdehyde (MDA) content while high concentrations (2% and 3%) increased it, indicating that low UPS supplementation may had a better effect on immune performance. 16S rRNA gene sequencing revealed that UPS supplementation reduced pathogenic populations. Function analysis showd that UPS may modulate metabolic pathways related to nitrotoluene and carbon source utilization. In summary, -derived BAP especially at low concentrations (1%) could enhance the nutritional composition, digestive and immune functions, and intestinal microbial community and metabolic profiles of juvenile sea cucumber. These findings provide a preliminary theoretical foundation for applying polysaccharides in aquaculture practices for sea cucumbers and other marine species.