Characterisation of endogenous long-chain polyunsaturated fatty acids synthesis and key enzyme functions in largemouth bass (Micropterus salmoides)

The long-chain polyunsaturated fatty acids (LC-PUFA) synthesis characteristics in fish, including the identification of key genes and their functional activities, are crucial for developing targeted nutritional strategies. Although the endogenous LC-PUFA synthesis capacity of largemouth bass ( Micropterus salmoides ) has been preliminarily reported, the key genes involved and their functional activities remain uncharacterized. In this study, we systematically validated the LC-PUFA synthesis pathway in largemouth bass by comparing diets supplemented with LC-PUFA (LD) or non-LC-PUFA (NLD). The results demonstrated that largemouth bass can endogenously synthesize LC-PUFA from C18 PUFA, albeit with compromised growth performance and hepatic health under NLD feeding. Furthermore, we characterised the genes potentially involved in LC-PUFA biosynthesis, including two fatty acid desaturases ( fads2a and fads2b ) and three fatty acid elongases ( elovl5 , elovl4a and elovl4l ). Bioinformatics analysis confirmed the evolutionary conservation of these genes and revealed the unique evolutionary divergence mechanism of the fads2s in largemouth bass. The LC-PUFA biosynthesis-related genes knockdown in primary hepatocyte and yeast heterologous expression confirmed that Fads2a has Δ4, Δ5, Δ8 desaturase activities and Fads2b Δ5, Δ6, Δ8 desaturase activities. And Elovl5 primarily participated in the elongation of C18 and C20 PUFA, whereas Elovl4a and Elovl4l were involved in the elongation of C18, C22 and longer-chain PUFA (> C24). Overall, we constructed a complete LC-PUFA synthesis pathway in the largemouth bass, thereby enhancing the understanding of the characteristics and evolutionary mechanisms of LC-PUFA synthesis in freshwater carnivorous fish. • Endogenous LC-PUFA synthesis from C18 precursors is confirmed in largemouth bass. • Highlighted trifunctional desaturase activity of two Fads2 in largemouth bass. • Elovl5 elongates C18-C20 PUFAs in largemouth bass. • Elovl4s elongates very long-chain PUFAs, essential for DHA synthesis. • Constructed the complete LC-PUFA synthesis pathway in largemouth bass.