The presence of nanoplastics (NPs) has been reported in aquatic systems all over the world, making them one of the emergent contaminants of greatest concern to the scientific community. In addition, predicted climate change scenarios are expected to lead to considerable fluctuations in environmental parameters, such as increases in salinity in certain coastal regions. The impact of variations in salinity and waterborne exposure to nanoplastics has been studied individually in a variety of aquatic species. However, given the fact that fishes are likely to encounter a combination of stressors in real-life scenarios, it is of utmost importance to investigate the possible synergistic effect of commonly occurring stressors. Furthermore, gilthead seabream (Sparus aurata ) is one of the most economically important species for the Mediterranean aquaculture industry, and climate change in combination with nanoplastic contamination might cause deleterious effects on the performance of the sector. Therefore, the present study aimed to investigate the effects of increased salinity levels and waterborne exposure to nanoplastics both alone and in combination, on the mucosal health of S. aurata .
To this end, juvenile gilthead seabream (14.2 ± 0.8 cm total length) were subjected to a 28-day challenge under four distinct experimental conditions, namely, Control (35 ppt, no NPs), Control salinity (55 ppt, no NPs), NPs (35 ppt, 1000 µg/L NPs), Salinity + NPs (55 ppt, 1000 µg/L NPs), using artificial seawater (AquaForest) and 44nm polystyrene NPs (PSNPs, Bangs Laboratory). Following exposure, fish were humanely euthanised and gills, gut and skin were sampled. The collected organs were processed to obtain cDNA from extracted RNA, and qPCR were performed to investigate the relative expression of genes related to the general stress response ( gr1, mr, hsp70), oxidative stress response (sod, cat), lipid metabolism (pparα), and immune response (tnfα , il10, il1β ).
The results suggest a slight effect of increased salinity on the investigated endpoints, showing an activation, to some extent, of the primary stress response, antioxidant mechanisms and immune response, with little to no effect of NPs alone. However, in some cases the combination of both stressors appears to have a synergistic effect on the expression of the studied genes. Overall, the data indicates tissue-specific responses to these stressors, with skin being the least impacted organ, and gills the most.