Molecular responses to pollution stress in glass eels (Anguilla anguilla): Gene expression changes associated with varying contamination levels and temperature across estuaries

Understanding the effects of global change is crucial to aid in the conservation of critically endangered species such as the European eel (Anguilla anguilla). Emerging pollutants (microplastics) and legacy ones such as heavy metals, as well as thermal pollution, are deleterious for this species; however, their molecular impacts on glass eels entering estuaries remain understudied. Investigating the molecular signatures of environmental stress can provide insights into some of the factors contributing to A. anguilla population decline. In this study, expression changes in candidate genes associated with general and thermal stress (hsp70 & hsp90), oxidative stress (sod1, sod2, cat, gpx1), heavy metal detoxification (mt2), and neurotoxicity (ache) were measured in gill tissue of glass eels exposed to polystyrene (PS) microbeads in an aquarium, and also in individuals sampled from six Bay of Biscay estuaries with different levels of microplastics, heavy metals, nitrites, nitrates and thermal pollution. In the aquarium experiment, a significant positive correlation was found between hsp70 expression and PS concentration. On the other hand, in the glass eels sampled from the wild results showed that gene expression patterns tend to cluster based on estuary's pollution levels. Specifically, hsp70 gene expression was upregulated in eels from the most polluted estuaries, suggesting signs of damage. This study highlights the molecular effects and signatures of emerging and legacy pollutants on the critically endangered European eel, under natural and controlled conditions.