Polysaccharides from Enteromorpha prolifera improve growth performance and are involved in regulation of immune responses and microbial communities in the sea cucumber, Apostichopus japonicus (Selenka, 1867)

A 70-day feeding experiment was conducted to investigate the effects of supplementing Apostichopus japonicus with polysaccharides from Enteromorpha prolifera (PEP) on growth performance, biochemical composition, immune responses, and microbial communities. Different proportions of PEP (0, 0.2,1, 5, and 25 g/kg) were respectively added to the basal diet. Dietary 5 g/kg PEP induced an increase in final weights and specific growth rates (SGR), while decreasing the ingestion rate (IR) and feed conversion efficiency (FCE). Moisture contents and crude protein levels of sea cucumber were not significantly affected by PEP supplementation. Superoxide dismutase (SOD) and acid phosphatase (ACP) activities were elevated by dietary 1 g/kg PEP supplementation. Alkaline phosphatase (AKP), total anti-oxidative (T-AOC), lysozyme (LZM), and catalase (CAT) activities were enhanced by dietary 5 g/kg PEP. Sea cucumbers fed with 5 g/kg PEP exhibited higher levels of lys and cystain, and suppressed rel levels. Based on 16S rRNA sequencing, it was found that dietary 5 g/kg PEP increased the relative abundances of Proteobacteria and Firmicutes, while decreasing the relative abundances of Lutibacter and Vibrio. In general overview, dietary 5 g/kg PEP improves growth performance, enhances non-specific immunity, and modulates intestinal microbial composition of A. japonicus.