Fucoidan from Undaria pinnatifida mitigates intestinal inflammation in Atlantic salmon (Salmo salar)

Using functional feed ingredients to increase the intestinal health of Atlantic salmon (Salmo salar) would allow for increased utilisation of plant-based proteins in the feed. This is beneficial both for the fish feed industry and the fish welfare. Fucoidans, a complex sulfated polysaccharide derived from marine macroalgae has great potential as functional feed ingredient due to its high bioactive properties. In the present trial, we challenged Atlantic salmon (Salmo salar) post-smolts with a low-level inflammatory model (soybean concentrate (SPC) in diet replaced by 17.8% soya HP48) supplemented with 0, 1 or 3% fucoidan extracted from Undaria pinnatifida (Control, FUC1 and FUC3, respectively). The fish were the diets in triplicates for 59 days. At the end of the experiment, the fish were sacrificed and the mid- and hind-intestine were sampled for histological-, integrity- (Ussing chamber) and gene expressional- (RNAseq) assessments. Addition of 3% fucoidan lowered the protein digestibility of the feed, however, this did not result in significant differences in the growth parameters. The paracellular permeability of the hydrophilic marker 14C-mannitol tended to decrease with the addition of fucoidan in both tissue segments. There was also observed an anti-inflammatory effect of fucoidan in the hind-intestine with significantly reduced stratum granulosum width and lamina propria height of fish fed FUC1 and FUC3 compared to the Control. Hence, this suggests that U. pinnatifida fucoidan has a positive effect on both intestinal integrity and immune regulation of Atlantic salmon (Salmo salar).