Alternative oils in salmon diets

A sustainable alternative to fish oils in salmon farming is vegetable oils. These are all devoid of VLCn-3 PUFA’s while the levels of 18:2n-6 (LA) and monoene fatty acids are usually high giving a low n-3/n-6 ratio. A few vegetable oils, such as linseed oil are high in 18:3n-3. However, in the new diets in stead of using single vegetable oils rapeseed oil, linseed oil and palm oil is combined to match the levels of saturated, monounsaturated and polyunsaturated fatty acids in fish oil. By doing this the aim of high digestibility and retention of VLCn-3 PUFA, high levels of fatty acids preferred for catabolism and high levels of precursor fatty acids (LNA) for elongation and desaturation to VLCn-3 PUFA is obtained. Concomitantly, n-6 fatty acid levels should be kept low to maintain a high n-3/n-6 ratio and high VLCn-3 PUFA beneficial to human health (Seierstad et al., 2005). For humans the desired ratio of n-3/n-6 is about 1:4, based on LNA and LA, and by blending vegetable oils for salmon diets the ratio of these fatty acids (LNA/LA) are kept higher than 1:4. The concern of human diets having excess of n-6 fatty acids is due to the fact that high LA give an over production of 20:4n-6 and an under production of EPA and DHA from LNA. With a LNA/LA ratio of 1:4 (0.25) this does not happen, and thus this dietary ratio is considered to be optimal. Importantly salmon fed vegetable oils contain the optimal or higher (Table 1) LNA/LA ratio in addition to high levels of the VLCn-3 PUFAs.