Dietary seaweed (Enteromorpha) polysaccharides improves growth performance involved in regulation of immune responses, intestinal morphology and microbial community in banana shrimp Fenneropenaeus merguiensis

The present study was conducted to evaluate the effects of marine polysaccharides from seaweed Enteromorpha on growth performance, immune responses, intestinal morphology and microbial community in the banana shrimp Fenneropenaeus merguiensis. Two thousand and four hundred juvenile shrimps with an average body weight of 2.18 ± 0.06 g were fed for 42 d with diets containing different levels of Enteromorpha polysaccharides (EPS): 0 (control), 1, 2 and 3 g/kg as treatment groups, each of group was replicated three times with two hundred shrimps per replicate. Dietary supplementation of 1 g/kg EPS showed a consistent improvement in the final weight, weight gain, average daily gain rate (ADGR) and specific growth rate (SGR) (P < 0.05), while showed a decrease in the feed conversion ratio (FCR) of shrimp (P < 0.05). Besides, the total anti-oxidative capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST), lysozyme (Lyz), alkaline phosphatase (ALP), and phenoloxidase (PO) activities in hemolymph were enhanced by dietary supplementation of 1 g/kg EPS (P < 0.05), while it reduced the hemolymph MDA content (P < 0.05). Shrimp fed 1 g/kg EPS supplemented diets up-regulated FmLyz, FmSOD5 and FmCLAP gene expression level of hepatopancreas and gill (P < 0.05), and also improved the intestinal FmLC2, FmLyz, FmSOD5 and FmCLAP gene expression levels (P < 0.05). In addition, shrimp fed diets containing 1 g/kg EPS increased the villus width (P < 0.05) and resulted in a higher villus surface area (P < 0.05). According to 16S rRNA sequencing results, dietary supplementation of 1 g/kg EPS tended to increase the relative abundance of Firmicutes at phylum level (P = 0.07) and decrease the relative abundance of Vibrio at genus level (P = 0.08). There was a significant positive correlation between the relative abundance of Firmicutes and mRNA expression of intestinal immune-related genes (P < 0.05). These findings revealed that dietary 1 g/kg EPS could improve growth performance, enhance nonspecific immunity and modulate intestinal function of banana shrimp F. merguiensis.