Transcriptomic Analysis Reveals Regulatory Responses of Fatty Acid Positional Distribution in Triacylglycerols and Lipid Composition to Dietary n-3 HUFA in the Muscle of Trachinotus ovatus

The nutritional value of lipids depends not only on their fatty acid composition but also on their stereospecific positioning on the glycerol backbone. This study investigated the fatty acid composition and <i>sn</i>-2 positional distribution of triacylglycerols (TAG), as well as the composition of major phospholipids in golden pompano (<i>Trachinotus ovatus</i>) juveniles (initial weight: 10 g) fed five diets including graded levels of dietary n-3 highly unsaturated fatty acids (HUFA; 0.64-2.10%) for 56 days. With increasing dietary n-3 HUFA levels, the proportions of eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), and total n-3 HUFA in muscle TAG, phosphatidylcholine (PC), and phosphatidylethanolamine (PE) significantly increased. Phospholipids, especially PC and PE, were preferentially enriched with n-3 HUFA, and the <i>sn</i>-2 positions of TAG showed a significantly increased deposition of DHA and reduced n-6/n-3 ratios. RNA-Seq analysis was performed on muscle tissues of <i>T. ovatus</i> subjected to different dietary n-3 HUFA levels to further investigate the molecular mechanisms of lipid compositional and structural changes. A total of 126,792 unigenes were obtained, of which 47.78% were successfully annotated. KEGG pathway enrichment analysis implicated the glycerophospholipid, glycerolipid, and sphingolipid metabolism pathways in lipid composition and distribution regulation, identifying <i>gpat4</i>, <i>agpat3</i>, <i>agpat8</i>, <i>lpeat1</i>, and <i>lpgat1</i> as potential regulators. These findings offer insights into lipid remodeling in marine fish and support strategies to enhance aquaculture product quality.