n-3 and n-6 fatty acids in farmed Atlantic salmon

Dietary experiments have shown that Atlantic salmon can be successfully grown on diets with as much as 100% replacement with a vegetable oil blend (Torstensen et al., 2005) when fish meal is used as protein source. EPA and DHA in fish meal, where these fatty acids are provided as phospholipids, is sufficient for meeting the Atlantic salmon requirement of EPA and DHA, and these fatty acids are highly efficiently retained in the fish (70% retention in vegetable oil fed salmon compared to 30 % retention in fish oil fed salmon). Furthermore, salmon fed a vegetable oil blend their entire life can get EPA and DHA levels similar to salmon fed fish oils their entire life. This can be achieved through a finishing diet a period before slaughter containing only fish oils in stead of vegetable oil blend (Torstensen et al., 2005). Fatty acid composition of farmed Atlantic salmon sampled from different commercial sites in 2001 (n=40) and 2005 (n=30) show how the fatty acid composition have changed over the last years with vegetable oil fatty acids (18:1n-9, LA and LNA) increasing and the VLCn-3 PUFAs decreasing. However, the levels of DHA have been kept relatively constant at 12 % and 17 mg per g flesh. Also, the LNA levels have increased from 2001 to 2005 to obtain an LNA/LA ratio higher than 1:4. Table 1 Fatty acid composition (wt%) and levels (mg per g flesh, w.w.) in farmed Atlantic salmon flesh sampled in 2001 and in 2005.