The main objective of the INTERACTION project, which fits with the One Health concept, is not only to improve the knowledge about the effects of an emerging contaminant on wildlife, but also to study its impact in combination with a biotic stressor on animal. This project will focus on the endangered species, Anguilla anguilla, experimentally exposed to realistic doses of bisphenol S as abiotic contaminant, and infected with the invasive nematode Anguillicola crassus (level of infection in accordance to our epidemiological data on European eels from Mediterranean lagoons). Bisphenol S (BPS), first presented originally as an environmentally-friendly alternative to BPA for a wide range of uses (additive to thermal paper and to dyes agents, a component of phenolic resins), is becoming an emerging environmental contaminant of concern. As the use of BPS as a BPA alternative grows, there is an urgent need to increase our understanding of the potential adverse effects of BPS under realistic conditions, in combination with biological stressors such as pathogens and parasites. The nematode parasite A. crassus, introduced in Europe in the early 1980s with imported Japanese eels, is recognized to negatively impact the European eels (A. anguilla). As we hypothesize that the combined effect of biotic and abiotic stressors affect eel physiology and decrease their fitness, compromising their ability to migrate and to reproduce, we consider that the impact of an emerging pollutant (BPS) in combination with an invasive parasite (A. crassus) constitutes a lack of knowledge that remains to be fulfilled. To reach the objective of the INTERACTION project, we will use a pluralistic approach to obtain an integrative view of the combined effects induced, through experimental controlled contaminations, on different processes (modifications of the microbiome, metabolome, transcriptome, peptidome, proteome). The expected results concern the identification of the main biological pathways of fish impacted by the multifactorial stress targeted in the project. At the swim bladder scale, we will also use an innovative approach in this field of research, MALDI mass spectrometry-based imaging, to reveal the local expression of the peptidome (histo-peptidomics) within the wall of this target organ in response to the developing parasite. As the mucus layer of the skin is the first barrier to the external environment for fish, continuously exposed to biotic and abiotic stressors, it appears relevant to explore the interrelationships between gene expression, metabolite production and variations in microbial community variations induced by BPS or/and A. crassus in this key protective barrier and to characterize biomarkers in order to provide a non-invasive proxy for the monitoring of eel’s health status. INTERACTION is an ambitious transdisciplinary project, conducted by a scientific consortium of high expertise, based on a relevant experimental approach with a pertinent biological model and using a wide range of high-end techniques.