Optimizing long chain-polyunsaturated fatty acid synthesis in salmonids by balancing dietary inputs

Abstract

The increasing use of terrestrial plant lipids to replace of fish oil in commercial aquafeeds requires understanding synthesis and storage of long chain-polyunsaturated fatty acids (LC-PUFA) in farmed fish. Manipulation of dietary fatty acids may maximize tissue storage of LC-PUFA, through increased production and selective utilization. A data synthesis study was conducted to estimate optimal levels of fatty acids that may maximize the production and storage of LC-PUFA in the edible portion of salmonids. Data were compiled from four studies with Atlantic salmon, rainbow trout, and steelhead trout (total n = 180) which were fed diets containing different terrestrial-based oils to replace fish oil. LC-PUFA (%) were linearly correlated between diet and muscle tissue (p < 0.001; r2 > 44%), indicating proportional storage after consumption. The slope, or retention rate, was highest for docosahexaenoic acid (DHA) at 1.23, indicating that an additional 23% of DHA was stored in the muscle. Dietary saturated fatty acids were positively related to DHA stored in the muscle (p < 0.001; r2 = 22%), which may involve membrane structural requirements, as well as selective catabolism. DHA was found to be optimally stored with a dietary n-3: n-6 ratio of 1.03: 1. These new results provide a baseline of optimal dietary ratios that can be tested experimentally to determine the efficacy of balancing dietary fatty acids for maximum LC-PUFA storage.

Influence of Dietary Long-Chain Polyunsaturated Fatty Acids and ω6 to ω3 Ratios on Head Kidney Lipid Composition and Expression of Fatty Acid and Eicosanoid Metabolism Genes in Atlantic Salmon (Salmo salar)

“…These as well as organ (i.e., liver vs. head kidney) differences may explain the discrepancies between studies. Further, dietary ratios of ALA:LNA were shown to influence LC-PUFA accumulation in salmonids and African catfish muscle tissues (Colombo et al, 2018 ; Sourabié et al, 2019 ), and this may have played a role in the regulation of LC-PUFA synthesis in our study. Finally, the positive impact of dietary EPA+DHA levels in our study could be related to MUFA levels, as the transcript expression of several lipid metabolism genes ( elovl5a, fadsd5 , and srebp1 ) showed a positive correlation with head kidney ΣMUFA ( Figure 3 ).…”

Freshwater, Landlocked Grand Lake Strain of Atlantic Salmon (Salmo salar L.) as a Potential Genetic Source of Long Chain Polyunsaturated Fatty Acids Synthesis

“…Eicosapentaenoic acid and DHA were negatively correlated with transcripts involved in LC-PUFA synthesis (elovl5a, elovl5b, elovl2, fadsd5, fadsd6a, and fadsd6b) in the liver in both strains (see Table 8), indicating that low levels of these FA in the liver causes upregulation of these transcripts, and vice versa; high levels of these FA result in down regulation of these transcripts. This type of feedback loop has been reported in other studies (e.g., Glencross et al, 2015;Betancor et al, 2016;Colombo et al, 2018). However, this was not the case for ARA (the n-6 LC-PUFA end-product) which was positively correlated with transcript expression.…”

Dietary lipid level and source affect metabolic responses in hybrid catfish (Pseudoplatystoma reticulatum × Leiarius marmoratus)

“…Abundant availability of dietary MUFA and SFA can decrease n−3 LC‐PUFA catabolism and result in greater deposition of these health‐promoting fatty acids in fish fillets (Colombo, Parrish, & Wijekoon, ; Rombenso, Trushenski, & Drawbridge, ; Trushenski, Crouse, & Rombenso, ; Turchini, Francis, Senadheera, Thanuthong, & De Silva, ). In this study, liver SFA was higher in fish fed diet FO 18% L, but no differences between oil sources were observed in muscle SFA.…”