Immunoendocrine response to individual or combined exposure of polystyrene nanoplastics and elevated salinity on gilthead seabream

The gilthead seabream ( Sparus aurata ) is one of the most important fish species in marine aquaculture, directly affected by different aspects of the “triple planetary crisis” (environmental contamination, loss of biodiversity, and climate change). This study aimed to elucidate the impact of two major components of this crisis, namely, elevated water salinity—as a direct consequence of climate change—and nanoplastics (NPs) pollution. The mucosal and systemic responses of juveniles ( S. aurata ) to exposure to high salinity and polystyrene (PS) NPs (PSNPs) both alone and in combination were assessed by analyzing the expression of relevant endocrine and immune genes in mucosal barriers (skin, gills, and intestine), as well as hematological and biochemical parameters in plasma. The results indicated tissue-specific responses to the experimental conditions, with intestine being the most responsive organ. Gills and skin were more heavily affected by exposure to salinity and PSNPs alone, respectively, and, in both cases, the combination of both challenges had a major impact compared with individual stressors. Similarly, significant hematological [white blood cell (WBC) and platelet (PLT) count] and biochemical [adenosine deaminase (ADA)] alterations occurred upon exposure to both stressors combined. Overall, the challenges induced the activation of the stress response of exposed fish, and elicited endocrine and antioxidant responses, particularly when exposed to the combination of high salinity and PSNPs. Altogether, this study highlights the role of mucosal surfaces when dealing with environmental and chemical stressors, and the importance of conducting co-exposure experiments to obtain a deeper, more realistic understanding of what aquatic organisms experience when challenged with several stressors conjointly.