Trophic ecology of the European eel (Anguilla anguilla) across different salinity habitats inferred from fatty acid and stable isotope analysis

Abstract

We combined fatty acid (FA) and stable isotope (SI) analyses to investigate the trophic ecology of different stages of European eels (Anguilla anguilla) across sea (SW), brackish (BW), and freshwater (FW) habitats. Salinity was the main driver of differences in the biochemical composition, and the greatest variation occurred between SW and FW eels. SW eels had a higher content of the FA indicator of carnivory, as well as the highest stable isotope ratios (C, N). In contrast, FW eels exhibited the highest lipid content and omega-6 polyunsaturated FA, but the lowest stable isotope ratios, suggesting major dietary differences between the eels in these two habitats. While the biochemical composition of BW eels was closer to those of SW eels, BW eels had the largest SI range, indicating higher dietary plasticity. FW individuals had better overall condition compared to SW eels. Independent of habitat, larger individuals were in the best condition, and had higher lipid content and monounsaturated FA. These findings suggest a biological advantage for eels to maintain a catadromous life-history strategy.

A multi-approach study to reveal eel life-history traits in an obstructed catchment before dam removal

“…In the Sélune catchment, our results indicate that the eel trophic level is influenced by their spatial distribution. As previously reported for eel, the trophic level appears higher in saline water (Parzanini et al 2021), but a gradient in δ 15 N was also observed between freshwater sectors, with a higher propensity to piscivory in the midstream and upstream sectors than in the downstream. This gradient probably reflects a specialization of eels in relation to prey availability (Cucherousset et al, 2011).…”

“…Although we observe high growth rate and trophic level for estuarine eels, the condition coefficient and lipid store contents are lower than for freshwater eels. Similar results were reported for eels in Norway (Parzanini et al 2021), but diverge from other watersheds where eels caught in brackish areas exhibited better body condition (Cairns et al, 2009;Daverat et al, 2012;Kaifu et al, 2013). One potential explanation is that sandy areas covering most of the Sélune estuary are poorly suitable for eel settlement, which is traduced by low body condition of eels living there.…”

“…For example, the size-and age-at-silvering greatly fluctuate along river catchments, with lower growth rates and older eels observed in upper reaches (Daverat et al, 2012), as opposed to eels residing in brackish waters, with earlier maturation and higher growth rates (Cairns et al, 2009). The condition of eels is also closely related to variation in their diet across different habitats, leading to changes in overall condition between marine, brackish and freshwater habitats (Parzanini et al 2021).…”

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.…”

Non‐lethal sampling for the stable isotope analysis of the critically endangered European eel Anguilla anguilla: how fin and mucus compare to dorsal muscle

“…SIA is frequently used in ecological studies of A. anguilla , where it has been used to identify their trophic ecology across salinity gradients (Harrod et al ., 2005), their dietary differences in relation to head morphology (Cucherousset et al ., 2011) and aspects of parasite infection (Pegg et al ., 2015). Although fin tissue is commonly used in eel SI studies ( e.g ., Cucherousset et al ., 2011; Musseau et al ., 2015), many studies still use dorsal muscle, with samples collected from euthanised fish ( e.g ., Capoccioni et al ., 2021; Parzanini et al ., 2021).…”