Fish oil accounts for approximately 26.8 % of the operating costs of salmon aquaculture. To compensate for the increasing demand in fish oil, alternative plant and animal oils have been used to replace the fish oil.
The goal of this study was to formulate a cost-effective fish feed which supports adequate growth of salmon and is less susceptible to oxidative damage while maintaining the characteristic beneficial fatty acid profile.
Experiments were undertaken to assess the growth, fatty acid profile, erythrocyte membrane fluidity, and ability of liver hepatocytes to convert linolenic acid to EPA and DHA in Atlantic salmon with inclusion of linseed oil into the diet. Salmon were fed for 3 months a control diet containing 100% fish oil (FO) and two experimental diets containing 60% FO/40% linseed oil (LO) or 20% FO/80% LO. After this period of time, all three groups were fed the 100% FO diet for an additional month. Specific growth rate showed consistent gains over the three month period with the 20% FO/80% LO giving the highest rate of growth of the three. During refeeding with 100% FO there was an increase in growth in all dietary groups, Fatty acid profiles also demonstrated some changes over the testing period with linolenic acid significantly higher, EPA significantly lower and DHA lower in experimental groups. After refeeding, linolenic levels declined while EPA and DHA increased. Membrane fluidity decreased when measured at 4°C and at 21°C in the fish fed the experimental diets. After 1 month of refeeding on the 100% FO finishing diet, the membrane fluidity displayed no significant changes at any temperature except for the TMA-DPH probe at 21°C. There was no apparent formation of EPA and DHA from linolenic acid.
Overall it is possible to replace fish oil in the salmonid diet with up to 80% LO as long as a finishing diet with 100% fish oil is administered. Therefore, substituting linseed oil for a large part of the fish oil will make a salmonid diet production more cost effective and environmentally sustainable.
