Dietary m icrominerals like iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), and selenium (Se) are essential nutrients playing critical roles in multiple physiological processes in fish (Baeverfjord et al., 2019; Prabhu, Schrama and Kaushik, 2016). Balancing these minerals in aquafeeds is vital for optimal growth, health, and immune function, particularly in challenging commercial fish farming conditions (Sommerset et al., 2023). As EU legislation imposes strict limits on mineral supplementation, knowledge of mineral availability from various sources is vital. In commercial salmon feeds, inorganic minerals are commonly used, yet their bioavailability and physiological impacts vary significantly (Maage and Sveier, 1998; Standal et al., 1999). S tudies across different fish species highlight the impact of variable mineral supplementation levels and sources (Buyinza et al., 2023 ; Kokkali et al., 2023; Nguyen et al., 2019; Xu et al., 2021) but most of these studies are performed under controlled conditions. O ur study sought to investigate the impact of essential micro mineral supplementation levels and source in commercial production settings along the Norwegian coastline , considering regional variations and challenges while assessing the mineral needs of farmed Atlantic salmon.
The study utilized four research farming licenses from the project "EINVU: Nutritional innovations – key to the big welfare challenges," across three regions along the Norwegian coastline. Atlantic salmon from approx. 500g body weight at the trial start to slaughter (approx. 4.5 kg), reared under commercial conditions (including e.g., lice and other therapeutic treatments), were fed 4 different diets containing either organic or inorganic minerals at two premix levels (Se: 0.7ppm, Cu: 22ppm, Mn: 69-81ppm, Zn: 166-199ppm and Fe: 248-318ppm). There were 2 replicate cages per treatment and trials were repeated in 3 different locations (North, Mid and West) and 2 stocking seasons (spring and autumn). General performance, whole body and tissue (filet, skin, liver, gills, milt, and kidney) mineralisation, biometrics, fish welfare and skin histology were studied.
Our study revealed a significant correlation between mineral level and fish performance parameters, final product quality, tissue mineralization, and skin histology. Decreasing dietary Fe levels by 22% and Mn levels by 15% showed no reduction in whole-body Fe or Mn levels in fish. Moreover, this reduction led to increased uptake of other dietary minerals, evidenced by elevated whole-body Cu and Mn, and fillet Cu and Fe, linked also with reduced fillet gaping. Moreover, supplementing Se and Zn at levels higher than legal limits boosted tissue concentrations without reaching saturation. Organic minerals were found to positively correlate with tissue mineralization in whole-body, fillet, and head kidney, with higher Cu levels in fillet linked to decreased fillet gaping. Additionally, the use of organic minerals positively impacted salmon’s fin score and slaughter yield. Finally, salmon survival, growth, welfare, and fillet quality, as well as tissue mineralization, were significantly influenced by the rearing location; emphasizing the importance of tailored mineral supplementation to meet their specific needs and environmental stressors, ultimately optimizing health and performance.