Introduction and Methodology
Feed additives derived from brown seaweed offer the potential to add value and unlock new market opportunities for algae cultivation. For instance, fucoidan from sugar kelp (Saccharina latissima) is a water-soluble sulfated polysaccharide that can be obtained through biorefinery processing (Michalak et al., 2023) for the development of novel functional aquafeeds (Rocha et al., 2025). Nevertheless, despite the reported intestinal immunomodulatory effects of fucoidan in salmonids (Rocha et al., 2025; Purushothaman et al., 2026), its comprehensive physiological impact on the host remains to be fully elucidated.
Currently, several methodologies are available to evaluate the properties of bioactive compounds in fish. For example, 'omics' strategies—such as transcriptomics, proteomics, and metabolomics—provide a general approach that can be complemented by the detection of specific indicators linked to both local and systemic physiological mechanisms. However, integrating and interpreting these miscellaneous datasets remains a significant challenge, yet this is essential for a overall characterization of the host's response. Addressing this issue through multi-layer analysis provides an effective framework for correlating diverse methodological outcomes. To assess this approach, we performed a Data Integration Analysis for Biomarker discovery using Latent cOmponents (DIABLO). DIABLO is an n-block sparse Partial Least Squares Discriminant Analysis (sPLS-DA). Accordingly, we integrated results on intestinal microbiota composition, proteomic profiles, and specific physiological parameters of Atlantic salmon (Salmo salar). These fish were fed fucoidan-supplemented diets for four weeks in freshwater, transferred to seawater, and subsequently exposed to inactivated Tenacibaculum maritimum, an emerging bacterial skin pathogen.
Results and Discussion
Based on DIABLO, the distal intestine (DI) of fish fed fucoidan-supplemented diets during the freshwater stage featured Lactiplantibacillus—a proposed probiotic in Atlantic salmon (Rocha et al., 2023)—as a prominent member of the microbiota. Furthermore, a cluster representing the expression of tnfa, cath2, and il8 (genes linked to innate immune activation) positively correlated with proteins involved in oxidative stress tolerance (B5XGZ2 and A0A1S3NRE4); mucosal barrier integrity (A0A1S3QBD3 and A0A1S3NMD0); and vesicular trafficking (A0A1S3T4X9). Interestingly, these indicators also showed a positive correlation with Enhancer of polycomb homolog 1 (A0A1S3NC89), a key protein linked to epigenetic regulation. Thus, these results suggested an activation/control of immune-related responses in DI. Similarly, DIABLO identified the gene expression of tnfa and cath2 as relevant features in the head kidney (HK), clustering together with anxa1 (a gene linked to immune homeostasis). Additionally, these biomarkers were associated with proteins involved in signaling and stress responses (B5XAP5); homeostasis and cellular maintenance (A0A1S3RWH8, A0A1S3RIW8, and B5X3X4); regulation of the actin cytoskeleton (B5X8M6 and A0A1S3R2S6); genomic, transcriptional, and epigenetic regulation (e.g., A0A1S3PGN9, B5X283, A0A1S3Q1N9, A0A1S3MUL1, B9ELF2, A0A1S3L589, B9EMR0); as well as energy demand (A0A1S3QT38). Therefore, the dietary inclusion of fucoidan would not only induce a local intestinal effect, but might also modulate the response in a major immune organ such as the HK. Regarding fish exposed to inactivated bacteria, the HK from fucoidan group showed the most relevant features after 24 hours. For instance, DIABLO detected a cluster of biomarkers connected with the expression of cytokines (il6, il4/13) and effector molecules, including antimicrobial peptides (cath2 and hepcidin) and arg1. These results suggest the activation and balance of M1 and M2 macrophage subpopulations, which were linked to proteins involved in transcriptional regulation (B5X9L2 and B9ELV7), cellular signaling and homeostasis (A0A1S3LJM0 and A0A1S3M624), physical organization and structural integrity (A0A1S3NL71 and B9ELR2), and energetic demand (B5XB07).
Overall, the multi-layered DIABLO framework overcomes the limitations of single-dataset evaluations, allowing for a deeper characterization of the host response. Furthermore, this holistic approach provides robust evidence that dietary fucoidan exerts local and systemic immunomodulatory effects.
Acknowledgment
We acknowledge the Research Council of Norway (RCN 329442, 294821) for supporting this study.
References
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