Fatty acid productive value and β-oxidation capacity in Atlantic salmon (Salmo salar L.) fed on different lipid sources along the whole growth period

The major aim of the current study was to evaluate the effect of substituting fish oil (FO) for a vegetable oil blend (VO) as dietary lipid source on lipid catabolism in Atlantic salmon (Salmo salar L.). The experiment endured from the start of feeding until the salmon reached 2.5 kg. Total and peroxisomal β‐oxidation capacities were determined in red and white muscle and liver. In addition, fatty acid productive value (FAPV) was calculated during the four time periods the experiment was divided into. In all the three tissues, an increased β‐oxidation capacity was found prior to seawater transfer; however, calculating the difference between the peroxisomal β‐oxidation capacity and the total, the peroxisomal β‐oxidation increased more than the mitochondrial β‐oxidation capacity. Hence, in liver and red muscle, 100%and 70%, respectively, of the total β‐oxidation capacity was accounted by peroxisomes prior to seawater transfer, compared with approximately 60% and 3% during the seawater phase. In contrast, white‐muscle mitochondria was the main organelle responsible for oxidizing fatty acids during the entire experiment (>90%). However, during the period of high energy demand (parr‐smolt transformation), fish fed VO exhibited significantly lower β‐oxidation capacity than fish fed FO, coinciding with low FAPV and low specific growth rate (SGR). Further, during periods of high growth rate, fish oxidized even essential fatty acids (18:2n‐6, 18:3n‐3, 20:5n‐3, and 22:6n‐3) when given in surplus. Low dietary levels of essential fatty acids gave significantly higher FAPV of these fatty acids in the whole body. However, the FAPV of 22:1n‐11 was low, indicating that this fatty acid is highly utilized as a substrate for β‐oxidation, irrespective of the dietary levels. There were no differences in whole lipid content between fish fed either FO or VO.