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Lipids, particularly fatty acids (FAs), are major sources of energy and nutrients in aquatic ecosystems and play key roles during vertebrate development. The European eel Anguilla anguilla goes through major biochemical and physiological changes throughout its lifecycle as it inhabits sea‐ (SW), and/or brackish‐ (BW) and/or freshwater (FW) habitats. With the ultimate goal being to understand the reasons for eels adopting a certain life history strategy (FW or SW residency vs. 'habitat shifting'), we explored differences in lipid content and FA composition of muscle, liver and eyes from eels collected across Norwegian SW, BW and FW habitats, and at different lifecycle stages (yellow to silver). FW and SW eels had a higher lipid content overall compared to BW eels, reflecting differences in food availability and life history strategies. SW eels had higher proportions of certain monounsaturated FAs (MUFAs; 18:1n‐9, 20:1n‐9), and of the essential polyunsaturated FAs 20:5n‐3 (eicosapentaenoic acid, EPA) and 22:6n‐3 (docosahexaenoic acid) than FW eels, reflecting a marine‐based diet. In contrast, the muscle of FW eels had higher proportions of 18:3n‐3, 18:2n‐6 and 20:4n‐6 (arachidonic acid), as is typical of FW organisms. MUFA proportions increased in later stage eels, consistent with the hypothesis that the eels accumulate energy stores prior to migration. In addition, the decrease of EPA with advancing stage may be associated with the critical role that this FA plays in eel sexual development. Lipid and FA information provided further understanding of the habitat use and overall ecology of this critically endangered species. [ABSTRACT FROM AUTHOR]

The article reports that fatty acids (FA) are a major source of nutrients and energy in aquatic food webs, as well as serving as the main components of all cell membranes. Topics include increasing anthropogenic impacts are predicted to selectively alter the production of these critical compounds, and the comprehensive assessment of these potential effects has synthesized and systematically explored differences in the abundance and distribution of FA in fish.