Atlantic salmon are the most economically important aquaculture species in Australia. Due to climate change, water temperatures in summer exceed the upper thermal tolerance limits of this species, leading to energy loss and a slower growth. Dietary lipid, particularly triglyceride (TAG), is the main energy source for Atlantic salmon, with viscera, muscle, and whole-body representing the key reservoirs for energy storage. High inclusion of vegetable oil (VO) in formulated feeds can lead to adiposity of viscera in Atlantic salmon. This may be at least in-part due to the high oleic acid (OLA; 18:1n-9) concentrations of some vegetable oils. Thus, our experiment tested the effect of high energy and high OA supplementation in a 2x2 factorial design on the growth performance and energy deposition of juvenile Atlantic salmon. This experiment investigates the potential for OLA as a functional ingredient to achieve energy fortification prior to summer.
An 18-week feeding trial was conducted in a freshwater recirculating aquaculture system (RAS). Juvenile Atlantic salmon initially weighed 71.9 g and 14 fish were stocked to each of the experimental tanks. The RAS was maintained under a 12 h light:12 h dark light cycle at 15 ? throughout and fish were fed twice a day according to the feed ration. The experimental diets were randomly allocated to three replicate tanks and consisted of i) a commercially relevant control diet, ii) a high oleic acid diet (HL), iii) a high lipid diet and iv) a high lipid diet with added high oleic acid sunflower oil (HLHO) providing four levels of dietary OA.
The results demonstrate that Atlantic salmon fed the HL and HLHO had significantly higher fillet yield compared to the control group despite no difference in growth performance parameters between treatments. Adipose tissue index showed an increasing trend with increasing OLA included in the diet, which, at least in part can be explained by an increase in the total lipid content of the adipose tissue. Atlantic salmon fed the HO diet had the highest lipid deposition in the adipose tissue and with the highest lipid apparent digestibility coefficient (ADC). Lipid class and fatty acid data will be presented and further explain lipid metabolism in the adipose tissue towards the identification of novel feeding strategies for summer welfare.