Effects of different dietary ingredients on the immune responses and antioxidant status in Atlantic salmon (Salmo salar L.): possible nutriomics approaches
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- Institutt for biologi 
The importance of salmon feeds Farming of Atlantic salmon (Salmo salar L.) is a first-rank aquaculture industry in Norway, accounting for a production of over 1.2 million tons per year. Dependency on fish meal has been considered a limiting factor hindering the sustainability of salmon production, as the use of small pelagic fish in the farming of Atlantic salmon is viewed negatively due to the resulting reduction of available marine protein in the ecosystem. Around 1,630,000 tons of biological ingredients are used annually to produce salmon feed for Norwegian aquaculture industries. Atlantic salmon can possibly be produced without reduction fisheries, but the quality and well-being of the salmon would need evaluation. For example, long-chain n-3 fatty acids (LC n-3 FAs) can be obtained directly from marine plants or from unicellular organisms, such as krill and Calanus. To understand the nutrient efficiency rate of farmed salmon, around 65% of salmon is consumed as human food, around 10% of trimmings of fillets are used as edible products for humans, and around 8% of the remainder is used to produce pharmaceuticals and omega-3 additives. Consequently, obtaining and establishing new feed ingredients to ensure nutritional efficiency and ecological safety are promising strategies in the Atlantic salmon industry. The major challenges in feeds development: molecular approaches The main challenge preventing these dietary modifications is the lack of a comprehensive understanding of all the immune-related pathways and molecules in fish species, and especially in Atlantic salmon. Different immunostimulants can be used as dietary interventions or medical treatments to investigate the activation or inhibition of different signals in innate and adaptive immune responses. The use of omics techniques allows researchers to identify networks of genes and proteins, while concurrently studying the total RNA, non-coding regions, splicing, and epigenetics using PCR and western blotting to analyze small numbers of targeted molecules. One of the main challenges facing omics investigations in fish species is the scarcity of available genomic and metabolic resources for most aquaculture species, which makes annotation, alignment, and visualization of gene networks and pathways quite laborious. The production of a proper immunity in response to antigens requires a dietary intake of nutrients that can reduce the risk of infections. Role of nutrition in the immune system Understanding the structure and function of innate immunity in bony fish species is essential for application of new techniques, such as transcriptomics, in nutrigenome and immunome studies. The fish immune system comprises two levels of reactions—innate and adaptive immunity—and dietary components can modulate the function of relevant immune pathways. The innate immune response includes all the defense components in the skin physical barrier, complement pathways, interleukins, and immune cells (like granulocytes, monocytes, macrophages and natural killer cells) that are present in fish organs before exposure to any pathogenic factors, and this response can be regulated by feeds prior to infection. Several studies have examined the association between nutrition status and the immune system in different organisms; however, the role of different types and amounts of nutrients on innate and adaptive immune signaling pathways is not completely clear. Inadequate dietary intake perturbs immune system components and can disturb the acute phase response and complement pathway activity. The use of different sources and amounts of nutrients can influence the immunocompetence of fish in ways that may be notably different from the responses of mammalian species. The known complex interaction of nutrients with immune related markers inspired us to conduct three animal trials to investigate on the effects of different lipid sources, functional feeds, and low or high LC n-3 FA diets on immune-related gene expression, protein levels, and enzymatic activities in wild, farmed, and elovl2-knockout Atlantic salmon at different stages of their life cycles. The bottom line Overall, this work contributes significantly to the understanding of functional genomics considering immunology, specifically the innate immunity and resistance against pathogens in a teleost fish prior to any pathogen or disease challenges. The gene, pathway, and network analyses helped to provide an overview of the different markers relevant to dietary ingredients and antioxidant status, in combination with protein levels of some transcription factors and nuclear receptors in a variety of tissues, including liver, intestine, muscle, and head kidney. To understand the association between feed and immunity can contribute largely to the aquaculture industry, fish and welfare and finally human wellbeing and production sustainability in a globalscale.