Exploring the bioactive properties of fucoidan from Sugar kelp to modulate the immune response and gut microbiota of Atlantic salmon

Long chain sulfated polysaccharides such as fucoidans are promising feed additives to improve animal health and welfare. Thus, based on in vitro and in vivo assays, our study evaluated the bioactive properties of fucoidan from sugar kelp ( Saccharina latissima ) on Atlantic salmon ( Salmo salar ). Data showed that salmon head kidney (SHK-1) cells increased their viability after 72 h post-incubation (hpi) with fucoidan at 500 μg mL −1 , while an up-regulation of antioxidant biomarkers (i.e., sod or prx2 ) was detected at 6, 24 or 24 hpi with fucoidan at 100 μg mL −1 . Furthermore, after a 5-week fish experiment with supplemented diets containing MacroGard® or fucoidan at 0.2 % (MG and F2, respectively), primary cultures from head kidney leukocytes (HKLs) of pre-smolts Atlantic salmon had an increased production of TNF-α and HSP70 at 6 hpi with proteins from Aeromonas salmonicida . In contrast, HKLs from fish fed fucoidan at 0.4 % (F4) increased IL-10 after 24 hpi with bacterial proteins. Regarding intestinal features, the dietary supplementation with fucoidan led to a higher relative abundance of Bacillus sp., whereas F2 group upregulated gata3 and pathways associated with lymph vessel development, chemotaxis, wound healing and cell migration (among others). This was also linked to increased levels of MHC II and CD3 in the gut, as well as with chaperones and proteins related to DNA repair, but with a lower abundance of transporters. Overall, these findings suggest that dietary fucoidan (depending on its inclusion level) can modulate salmon immunity and gut microbiota, supporting the further exploitation of this compound in health-promoting functional feeds. • Fucoidan modulated antioxidant and pro/anti-inflammatory biomarkers in salmon cells. • Intestinal abundance of Bacillus sp. correlated with fucoidan levels at in vivo level. • Innate and adaptive immune mechanisms were activated in gut from fish fed fucoidan. • Fucoidan increased chaperone abundance and proteins linked to DNA repair in gut.