Sammendrag
During different production stages, salmon farming industry faces multi-stressor conditions (e.g. diseases, sub-optimal nutrition, handling and environmental problems) that can cause economic losses. In recent years, there has been a great interest to develop novel feed molecules for use in functional feeds to improve fish health and welfare. To help in the search for these molecules, Food of Norway, a Center for Research-based Innovation and its spin-off project Resilient salmon are working on obtaining bioactive compounds and characterizing their immunomodulatory properties.
We evaluated the potential of fucoidan, which is a natural polysaccharide extracted from sugar kelp (Saccharina latissima), as a functional ingredient in feeds for Atlantic salmon (Salmo salar) pre-smolts. For this, fish (30 g) were fed (in triplicate tanks) for 30 days with a control diet (commercial-like plant-based diet: CD) or with a test diet (CD supplemented with 0.2% of fucoidan: FD). At the end of the trial, distal intestine (DI) from 9 fish per diet were collected. Considering that DI is a Mucosa-associated lymphoid tissue (MALT), transcriptomic analysis (by RNAseq) and specific detection of immune-related biomarkers at gene expression and protein level were performed (by qPCR and immunohistochemistry, respectively). In addition, 16S rRNA sequencing was carried out to assess microbiome composition.
The results showed that FD modulated microbiome composition in DI (increased the relative abundance of the genus Bacillus), and induced upregulation of differentially expressed genes (DEGs) related to pathways such as extracellular matrix binding, lymph vessel morphogenesis, blood vessel endothelial cell differentiation, cell population proliferation, ECM-receptor interaction and glycosaminoglycan binding. In addition FD led to downregulation of DEGs involved in serine-type endopeptidase inhibitor activity, negative regulation of molecular function and negative regulation of cellular protein metabolic process. Moreover, an increase in the expression of gata3 was detected in DI (FD group), along with higher protein levels of CD3, CD8 and MCHII. These data suggest that the inclusion of fucoidan as a feed additive in functional feeds is able to prime the immune system of Atlantic salmon, modulating aspects related to T cell polarization in DI. To assess whether these responses are beneficial to the fish during multi-stressor conditions, we are currently conducting a challenge trial with Atlantic salmon fed FD and exposed to Tenacibaculum dicentrarchi after seawater transfer.
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