It is a major challenge to maintain healthy fish and high welfare standards, while also increasing the environmental sustainability of salmon feeds. Every year over 10 million Atlantic salmon deaths are reported from the marine phase, resulting in over £1.6 billion losses globally. Mass mortality events at this stage are increasing in all farming nations year on year associated with a range of infectious diseases and spectrum of different pathogens.
While farmed salmon were traditionally fed diets rich in fish oil, currently most of it is replaced with vegetable oil. Vegetable oils have more short chain n-6 Polyunsaturated Fatty Acids than fish oils, which promotes tissue adipogenesis leading to deposition of fat depots in the salmon viscera. The polyamine spermidine enhances life span in various species via upregulation of autophagy, a cellular mechanism of protein and lipid breakdown. It is cardioprotective, improves β- oxidation and boosts the antiviral response in aging mice. In juvenile salmon, dietary supplementation of arginine, which leads to spermidine biosynthesis, improves metabolic status by enhancing β- oxidation of long chain fatty acids. We hypothesized that adding spermidine to a vegetable oil enriched salmon diet will enhance the breakdown of lipids through autophagy, leading to a range of health benefits.
We fed salmon with a soy oil rich diet (80:20, soy oil: fish oil) supplemented with 5mg/Kg of spermidine. After 5 weeks, we measured free fatty acids (FFAs) in the visceral fat . FFAs were measured using HPLC coupled with a Triplequad mass spectrometer. Analysis was performed with Multiple Reaction Monitoring in negative mode, with at least two mass transitions for each compound. Quantification of FFAs was obtained using Supelco 37-component FAME-Mix in relation to deuterated internal standards.
Our results show an increas e in the release of long chain FFAs and n -3 FFAs in adipose tissue from visceral fat (Figure 1, A&B) . Furthermore, we observed upregulation of Carnitine Palmitoyltransferase 1A (CPT1A) in the white muscle (Figure 1, C&D). CPT1A is a mitochondrial inner membrane enzyme required for the transport of FFAs to the mitochondria for β- oxidation.
We propose that addition of spermidine in salmon diets can be immunomodulatory by providing ATP for active immune cells and release of desirable omega-3’s which are anti-inflammatory.