Impact of dietary iron on the LC-PUFA biosynthetic pathways in Platynereis dumerilii

The long-chain polyunsaturated fatty acids (LC-PUFA) are essential lipids for key physiological processes in animals. Marine polychaetes can endogenously biosynthesise these LC-PUFA through a process mediated by elongases and desaturases, making them promising candidates to support the replacement of fishmeal and fish oil in aquafeeds. Enhancing this biosynthetic ability could lead to the production of marine ingredients with improved nutritional value. This study evaluated whether dietary iron (Fe), a cofactor of fatty acyl desaturases, can enhance LC-PUFA biosynthesis in the marine polychaete Platynereis dumerilii, used here as a model species. A feeding trial was conducted under two salinity regimes (35‰ and 40‰) and two dietary treatments (Without Fe Supplementation and With Fe Supplementation), assessing growth, expression of key desaturases and elongases, and fatty acid profiles. The highest growth performance was recorded in worms reared at 40‰ and fed the Fe-supplemented diet. No change in the expression of LC-PUFA biosynthesis genes was observed across treatment conditions; however, clear effects were detected at the biochemical level. Salinity and Fe significantly influenced the fatty acid composition, with polychaetes at 40‰, especially those receiving Fe, exhibiting higher proportions of LC-PUFA, notably arachidonic acid and 20:3n-6. These results indicate that Fe can enhance LC-PUFA biosynthesis when the pathway is metabolically activated, such as under elevated salinity. Overall, this study identifies salinity and dietary Fe as complementary factors that increase LC-PUFA levels in a polychaete model, providing valuable insights for strategies aimed at enhancing the nutritional quality of marine invertebrates for sustainable aquaculture.