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

## TL;DR

This study examines how gilthead seabream respond to environmental stressors like high salinity and nanoplastics, finding that combined exposure has a stronger impact than individual stressors.

## Contribution

The study introduces a novel co-exposure approach to assess the combined effects of nanoplastics and elevated salinity on fish immune and endocrine systems.

## Key findings

- The intestine was the most responsive organ to stressors, with significant gene expression changes.
- Combined exposure to salinity and nanoplastics caused greater effects than either stressor alone.
- Hematological and biochemical changes were observed, indicating a stress response in exposed fish.

## Abstract

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.