Microplastics and nanoplastics induced differential respiratory damages in tilapia fish Oreochromis niloticus

With the increasing micro(nano)plastics (MNPs) pollution in aquatic environments, fish respiration is encountering a huge threat. Herein, polystyrene (PS) MNPs with three sizes (80 nm, 2 mu m, and 20 mu m) were exposed to tilapia Oreochromis niloticus at an environmentally relevant concentration of 100 mu g/L for 28 days and their impacts on respiratory function were investigated. Based on the results of oxygen consumption and histological analysis, all the three treatments could induce respiratory damages and such impacts were more severe for the 2 mu m and 20 mu m treatments than for the 80 nm treatment. These results were explained by the more significant upregulation of egln3 and nadk, and the downregulation of isocitrate. Transcriptomics and metabolomics further revealed that TCA cycle played a key role in respiratory dysfunction induced by micro-sized PS particles, and cytokine and chemokine related functions were simultaneously enriched. Although nano-sized PS particles had the potential to penetrate the respiratory epithelium and reached the internal structure of the O. niloticus gills, they were easily expelled through the blood circulation. Our results highlighted the serious threat of MNPs to fish respiration and provided insights into the differential toxicological mechanisms between micro-sized and nanosized particles, thus assisting in ecological risk assessments.