Spatial and seasonal variations of methylmercury in European glass eels (Anguilla anguilla) in the Adour estuary (France) and relation to their migratory behaviour

Abstract

Overall recruitment of European glass eels (Anguilla anguilla) has decreased significantly since the early 1980s. Due to their long life cycle, benthic/demersal habits and high lipid content, eels might accumulate high concentrations of contaminants, but data concerning glass eels are still scarce. This study provides original data on methylmercury (MeHg) concentrations in glass eels at spatial (marine and estuarine), annual and seasonal scales. The relationship between MeHg concentrations in glass eels and their propensity to migrate up estuaries was also investigated. MeHg data were individually related to the eels' energetic condition which was estimated by dry weight. Glass eel migratory behaviour was investigated in an experimental flume and related to the MeHg concentration and dry weight at the individual scale. Marine and estuarine glass eels were caught from 2004 to 2011. There was a strong inverse correlation between MeHg concentrations and dry weight. MeHg concentrations increased in marine and estuarine glass eels from 2004 to 2009 and from 2004 to 2010, respectively, and then, both groups decreased in 2011. On a seasonal time scale, MeHg concentrations were higher at the end of the fishing season (April). MeHg bioaccumulation is likely to result from different sources, but the lack of significant differences between marine and estuarine glass eels suggests that direct contamination during estuarine migration is low. Other sources such as maternal transfer or oceanic contamination are discussed.

Looking at the complex relationships between migration behavior and conditional strategy based on energy metabolism in the European glass eel (Anguilla anguilla)

“…Final wet weight was highly correlated to tryglycerides (see section 1.2) and wet weight was considered in this study as a good proxy of energy stores. Here we show that autumn glass eels displayed higher wet weight than spring ones, which is in close agreement to previous observations made in A. anguilla glass eels (Charlon and Blanc, 1982;Claveau et al, 2015;De Casamajor et al, 2000;Elie, 1979). Such seasonal differences in biomass and energetic stores have been suggested…”

“…For this purpose, we characterized the individual's energetic status of glass eels in terms of wet weight (as a proxy of energy stores), standard metabolic rate (SMR) and transcriptomic profile of metabolism-related genes and determined the relationship of these energy-and metabolism-related factors with the propensity to migrate of glass eels, as evaluated in experimental condition. In order to strengthen the possible link between energetic status of glass eels and their propensity to migrate, we used glass eels arriving at the mouth estuary in autumn and spring known to present high and low energetic stores, respectively (Charlon and Blanc, 1982;Claveau et al, 2015;De Casamajor et al, 2000;Elie, 1979).…”

Bioaccumulation of Metals in Eels Taken From Lakes Köyceğiz (Turkey) and Võrtsjärv (Estonia) and Health Risk Assessments

“…Bioaccumulation of toxic metals in eels has a significant impact on its physiology. The high toxic metals such as Cd, Pb, and Hg can impair the immune, reproductive, nervous, and endocrine systems, thus negatively affecting cellular and organ functions at the individual and even population level (Romero et al 2020;Claveau et al 2015;Pierron et al 2008;Riberio et al 2005). The concentrations of Cd in the liver, gill, and skin tissues of eel from both lakes were measured approximately 10 times higher than the concentrations of Cd in the muscle (Table 2).…”

Metabolomics to Study the Sublethal Effects of Diazepam and Irbesartan on Glass Eels (Anguilla Anguilla)

“…The energetic conditions of glass eels, as described by Claveau and co-workers (Claveau et al, 2015), and contamination, could also influence this migratory behaviour. Likewise, the European eel shows environmental sex determination, and estuarine migration influences sexual differentiation (Davey and Jellyman, 2005;Harrison et al, 2014).…”