Addressing the impact of mercury estuarine contamination in the European eel (Anguilla anguilla L., 1758) – An early diagnosis in glass eel stage based on erythrocytic nuclear morphology

Highlights: • Hg induced genotoxicity and alterations on haematological dynamics of glass eel. • Erythrocyte nuclear morphology is suitable to identify fish exposure to Hg. • EMI arises as a new and useful tool for assessing aquatic contamination. • Caging is a suitable approach to assess short-term Hg exposure using migratory fish. • Hg challenge at the beginning of continental phase may impact adversely eels' populations. - Abstract: The decline of the European eel (Anguilla anguilla L., 1758) population throughout Europe has been partially attributed to pollution. As glass eel estuarine migration may represent a considerable threat, the impact of mercury (Hg) contamination at this stage was evaluated through an in situ experiment (7 days). Total Hg (tHg) bioaccumulation was evaluated concomitantly with erythrocytic nuclear morphology alterations: erythrocytic nuclear abnormalities assay (ENA), frequency of immature erythrocytes (IE) and the erythrocytic maturity index (EMI). The ENA results suggested a genotoxic pressure at the most contaminated sites, in line with the tHg increase. The EMI data, together with IE frequency, showed that fish exposed to high levels of Hg exhibited alterations of haematological dynamics, translated into an erythropoiesis increment. Despite the presence of these compensatory mechanisms, the present findings suggest a harmful impact of Hg on genome integrity at this early development stage, potentially affecting eels' condition and ultimately the population sustainability.