Metabolic pathways and physiological functions of organic and inorganic trace minerals in Atlantic Salmon

Summary

Mineral nutrition plays a key role in the health, welfare, and performance of farmed Atlantic salmon (Salmo salar), as it influences various physiological processes essential for growth, metabolism, and immune function. Among the essential trace minerals, zinc (Zn), copper (Cu), manganese (Mn), iron (Fe), and selenium (Se) are particularly crucial, serving as cofactors for numerous enzymes involved in vital biochemical reactions. In the context of modern aquafeed formulation, the composition and bioavailability of these minerals are of high importance, especially as aquaculture shifts towards plant-based diets. Understanding the dynamics of mineral nutrition in farmed salmon is essential for optimizing feed formulations to secure performance, enhance fish welfare, and ensure sustainable aquaculture practices. In aquafeed formulation, inorganic minerals (IM) are commonly used due to their cost-effectiveness and stability. These minerals are typically derived from mineral salts and oxides. While inorganic minerals are readily available and relatively inexpensive, their absorption and utilization by fish can vary depending on factors such as water pH and dietary interactions. In the past decade, there has been a notable trend in animal nutrition towards the development of organic minerals (OM), including chelated minerals and proteinates, which offer enhanced bioavailability and stability compared to their inorganic counterparts. Chelated minerals are bound to organic molecules, such as amino acids or peptides, facilitating their absorption and utilization in the fish's body. This increased bioavailability can lead to improved nutrient utilization, enhanced growth performance, and better overall health in farmed fish. Organic mineral sources also have the potential to mitigate the negative effects of anti-nutritional factors present in plant-based diets, like phytic acid, thereby promoting optimal mineral status and physiological function in fish. The main goal of this study was to map the physiological implications of supplemental dietary essential trace minerals (Zn, Cu, Mn, Fe and Se) in farmed Atlantic salmon. Emphasis is placed on release rate to the environment and importance for fish welfare, health and performance related to differential uptake, assimilation and function mechanisms involved when dietary essential trace minerals, are provided at different levels and forms, namely organic or inorganic. Paper I investigates the effects of OM and IM supplementation on the growth, nutrient utilization, and fillet quality of Atlantic salmon smolts. Using a factorial design, eight experimental diets were administered, containing graded levels of either organic or inorganic Zn, Cu, Mn, Fe and Se. The study revealed a trend towards higher growth rates in groups receiving OM, regardless of the mineral levels in the diet. Moreover, OM showed improved digestibility and retention efficiency compared to their inorganic counterparts. Fish fed OM exhibited higher levels of EPA and DHA, increased slaughter yield, and improved fillet quality. Additionally, the study explored various effects on fillet yield, bone strength, skin morphology, organ mineralization, and midgut transcriptome based on the source and dietary inclusion levels of trace minerals. While mineral nutrition experiments often occur under controlled conditions with minimal stress and for short durations, the transition to commercial settings presents numerous challenges. In this context, Paper II aimed to bridge the gap between controlled trials and real-world commercial aquaculture operations. By conducting trials in commercial farms, this study assess the practical implications of mineral supplementation level and source under the diverse and dynamic conditions encountered in commercial aquaculture settings. This approach allowed for a more comprehensive understanding of how mineral supplementation influences the welfare, health, and performance of farmed Atlantic salmon in environments characterized by fluctuating stressors and operational complexity. Paper II presents findings from 12 commercial salmon farming trials, investigating the practical effects of varying dietary mineral levels (ML) in both organic and inorganic forms. Conducted across four full-scale feeding trials in three distinct locations along the Norwegian coast (North, Mid and West regions), the study includes replication of the nutritional interventions for both 1+ and 0+ smolt. Factors such as fish age, farm location, ML, and their interactions play crucial roles in shaping growth, feed conversion, mortality, and production outcomes. Notably, mortality rates were influenced by smolt age and farm location, with “Mid” farm demonstrating lower rates compared to others. ML affected the quality of slaughtered fish, with different levels yielding varying proportions of “Superior” category produced fish. Additionally, mineral sources influenced slaughter yield, with organic minerals showing higher rates. Filet yield and gaping in the filet were also significantly influenced by mineral level and farm location. The mineralization and chemical composition of various tissues were found to be correlated with the design factors; while skin histology revealed notable regional differences influenced by interactions among mineral levels, mineral source, and farm location. Paper III investigated the molecular expression of mineral transporter genes (ctr1, dmt1, selp, zip7, and zip14) in the gastrointestinal tract of Atlantic salmon sampled from the West region, exploring the absorption mechanisms of trace minerals and assessing the impact of dietary mineral level and source on intestinal absorption.

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NVA : hdl.handle.net/11250/3148775