Abundance of long-chain polyunsaturated fatty acids in European eel (Anguilla anguilla L.) is determined by diet rather than biosynthesis.

The European eel (Anguilla anguilla L.) exhibits a remarkable phenotypic plasticity by occupying both marine and freshwater habitats and transitional areas in between. Because these habitats are characterized by different food sources with different fatty acid compositions, it remains unclear how eels from different habitats obtain essential long-chain polyunsaturated fatty acids (LC-PUFAs) to integrate in their lipids. We studied whether the fatty acid composition of eels in three different habitats, that is, a marine lagoon, an estuary, and a river, could be related to the expression levels of genes involved in the LC-PUFA pathways. In general, there were no significant differences in gene expression between eels from marine and freshwater habitats; gene expression in marine and freshwater specimens significantly differed from eels caught in the estuary. However, levels of essential LC-PUFAs and fatty acid ratio markers differed significantly between eels from the river and the marine lagoon. Therefore, we conclude that the LC-PUFA composition of the European eel is likely defined by their food intake from the local environment they are living in and potentially affected by the prevailing conditions, such as food availability, temperature, and salinity.