Trained immunity and nutritional programming for resilient salmon

Trained immunity and nutritional programming for resilient salmon («RESILIENT SALMON») Aquaculture is an important economic sector for Norway and the world. However, the continued growth of this industry has several challenges. RESILIENT SALMON will contribute to increased growth and value creation in the Norwegian salmon industry by developing a more robust fish with the ability to handle multi-stressor conditions (e.g., sub-optimal nutrition, diseases, and environmental problems) through an improved immuno-nutrition strategy. To achieve this, we combine in vitro screening experiments using salmon cells and in vivo feeding trials using fish exposed to microbe-associated molecular patterns (MAMPs), seawater transfer, pathogen outbreaks and short-term hypoxia. Fish responses were documented using a multi-omic approach and by detection of specific biomarkers. The results showed that salmon cells induced with fucoidan from seaweed and microbial ingredients derived from yeasts (LAN4 and LAN6) were able to stimulate immune responses, activating and controlling the production of different biomarkers (e.g., cytokines and effector molecules), which may be crucial for fish homeostasis and welfare. Based on these data, we evaluated novel functional feeds for Atlantic salmon with the inclusion of these bioactive compounds. In an acute hypoxia stress trial, LAN4 was able to modulate the fish´s physiological response, regulating the plasmatic secretion of cortisol and IL-10 (preventing immunosuppressive states), and increasing the levels of Muc-like proteins in the distal intestine, while in gills, the upregulation of metabolic pathways associated with stress-tolerance was detected. Furthermore, during an early natural outbreak of Moritella viscosa, which causes winter ulcers (skin wounds) in Atlantic salmon, vaccinated fish fed LAN6 showed a higher production of specific immunoglobulins against this pathogen, in addition to an upregulation of functional pathways associated with humoral immunity and complement activation in the liver. These results suggest that LAN6 could be a good candidate for functional feeds for salmon to achieve a more resilient fish against stressor conditions. Functional feed containing fucoidan extracted from sugar kelp has shown promising effect on gut microbiota and immunomodulatory function in fish. For instance, fucoidan modulated the composition of gut microbiome in Atlantic salmon (increasing Bacillus spp), and led to an upregulation of genes related to lymph vessel morphogenesis, cell proliferation and differentiation, which may involve priming the immune system of Atlantic salmon by modulating T cell polarization in the distal intestine. This may be associated to the detection of with higher protein levels of cell-surface markers (e.g., CD3, CD8, and MCH-II), as well as the upregulation of gata3 (global transcriptional factor related to Th2-cell activation), which is crucial for antibody production and coordination of adaptive immune responses. In a follow-up trial, we have also detected that feed containing fucoidan improved growth performance and modulate trained immunity (by increasing the expression/production of antimicrobial peptides) in salmon against a challenge with MAMPs from an emerging bacterial pathogen (Tenacibaculum maritimum) during seawater stage. Taken together, use of functional feed with seaweed extracts and nutritional programming can help achieving a more robust salmon.

RESILIENT SALMON will increase growth and valorization of the Norwegian aquaculture industry by developing robust salmon with enhanced innate immune resistance. We will boost the performance and resilience of Atlantic salmon by investigating the effect of bioactive compounds derived from lignocellulosic biomass and brown macroalgae as bioactive feed components in optimized feed formulations. A specialized cellulose feed matrix will ensure efficient, targeted delivery of the bioactive compounds to the mid- and hindgut. By comparing salmon with low vs. high resilience, the genetic basis for distinct responses to diet and stress will be identified. Trained immunity, nutritional programming, and targeted delivery of bioactive compounds will be used during the freshwater phase for innate immunotraining and to shape host-microbe interactions to enhance the survival and productivity of post-smolt salmon. Our team of experts will apply the latest techniques including functional metagenomics, transcriptomics, metabolomics, and advanced phenotyping of immune cells. Immunostimulation and pathogen challenge studies will be conducted to verify immune-training both in vitro and in vivo. Our multi-omics approach will identify linkages between specific feed components and the complex gut microbiome, identify pathways for the production of specific metabolites, reveal the multitude of microbial interactions with gut cells, and identify fundamental aspects of induced immune responses in the host. The principle goals of this project are 1) to generate a broad understanding of the biological and environmental factors determining fish resilience and 2) to develop tools to assess immune training and health in salmon. Thus, the RESILIENT SALMON project will employ trained immunity, nutritional programming, and novel encapsulation technology to produce robust salmon in experiments that explore multiple stressors (pathogens, handling stress and seawater adaptation).