Energy modulation in Atlantic salmon: Oleic acid increases adipogenesis and energy deposition

Due to climate change, water temperatures in Tasmania (Australia) summer are rising at 0.4 °C per decade, exceeding the upper thermal tolerance limits of Atlantic salmon, leading to reduced feed intake, increased metabolic rate, and energy loss. These suboptimal conditions affect growth performance and quality of the final products. Thus, higher energy storage in salmon tissue prior to summer has been envisaged as a strategy to minimise the detrimental effects of this culture phase. The objective of this study was to investigate if dietary oleic acid could increase energy storage in visceral adipose tissue of juvenile Atlantic salmon reared under pre-summer conditions (15 °C), primarily as triacylglycerols, and assess whether it was more effective than high-lipid diets for energy modulation. For this, four diets were formulated and manufactured with two different levels of oleic acid (high and low) and two different total lipid (high and low) and fed to Atlantic salmon (71.8 ± 0.20 g) for 124 days. The results showed Atlantic salmon fed high-lipid diets demonstrated higher growth performance compared to the low-lipid diets, with a significantly lower feed conversion ratio, higher digestible energy retention, and higher triacylglycerol concentration in the fillet. High-oleic acid diets resulted in significantly higher total lipid and triacylglycerol concentrations in visceral adipose tissue compared to low-oleic acid diets. This was achieved via adipocyte hyperplasia originated from the increased provision of the energy substrate, oleic acid, in visceral adipose tissue lipid for triacylglycerol synthesis. Diets containing low lipid and high oleic acid accumulated the highest metabolic energy in visceral adipose tissue and can be considered a viable energy modulation strategy for Atlantic salmon. However, further investigation is needed to understand the long-term effects of triacylglycerol accumulation on fish health to ensure commercial viability.