Feeding habitat and silvering stage affect lipid content and fatty acid composition of European eel Anguilla anguilla tissues

Abstract

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.

Seasonal Differences in Lipid and Fatty Acid Composition of European Eels (Anguilla anguilla, Linnaeus 1758) from Orontes River, Turkiye

“…In this study, lipid contents ranged between 23.12% ±0.47 and 30.32% ±0.54 in yearlong sampling. Our findings were comparable to those of Parzanini et al (2021). According to Ackman (1990), samples with more than 8% fat content are classified as high fat.…”

“…As opposed to other fish species, eels store their lipids in between fibers of muscle tissue, and fat can comprise up to 55% of the eel's body (dry) weight (Lovern, 1938;Henderson & Tocher, 1987). Also, for the success of migration and spawning, eels require high-fat content in their muscular tissue (Larsson et al, 1990) and they accumulate these lipids before migration (Durif et al, 2005;Parzanini et al, 2021). This situation is also compatible with our lipid values.…”

“…Most of the MUFA in this study was identified as oleic acid, highest in winter. This is consistent with the hypothesis that in winter, the eels accumulate energy stores before migration (Parzanini et al, 2021). In contrast to this, total PUFAs were not as high as expected in winter.…”

Habitat use and growth of yellow-stage European eel in coastal and freshwater ecosystems in Norway

“…Compared to eel in most of the eel distributional range, Norwegian eel grow relatively slowly and need more years to reach maturity. Although eel freshwater growth rates are generally lower (Daverat et al 2012; present study) and parasitic threat is higher than in marine habitats, there are also benefits for freshwater resident eel such as somewhat greater energy stores and higher contents of certain essential fatty acids (e.g., arachidonic acid) that are key for maturation and reproduction (Parzanini et al 2021a(Parzanini et al , 2021b. A thorough Can.…”

Role of estuarine habitats for the feeding ecology of the European eel (Anguilla anguilla L.)

“…Insecta, Gasteropoda and Polychaeta prey were the most widespread other prey taxa, with low %IRI values below 3%. The high diversity of prey recorded in the gut contents confirms the opportunistic character of European eels, particularly in feeding on benthic prey [83][84][85].…”