Real-time monitoring of microplastic accumulation in fish bodies using transparent goldfish revealed initial attack on the gill

To investigate the adverse effects of microplastics (MPs), we conducted an analysis using transparent goldfish (Carassius auratus). Transparent young goldfish were exposed to chronic toxicity concentration of fluorescently labeled microplastic beads (FMPs) and tracked their uptake into the body. During the four-week (28-day) treatment period, photographs of three parts of the goldfish were taken every week to track the localization of FMPs. FMPs were initially observed in the intestines, but from Day 14 onward, accumulation in the gills began to be observed. In the FMP-treated group, the number of individuals who died rapidly increased from Day 21. In deceased individuals, the accumulation of FMPs in the gills was prominent, suggesting that accumulation in the gills was the primary cause of death. Histological examination of the gill cells revealed that the epithelial cells of the secondary lamellae had died and that the central pillar cells and erythrocytes remained. TUNEL staining revealed a significant increase in cell death in the FMP-treated group. Confocal microscopic observation demonstrated that FMPs were bound to the cell surfaces and also invaded the cells. These results suggest that cell death is caused by the binding and invasion of MPs into gill cells. Based on these results, one of the adverse effects of MPs on fish is presumed to be a decrease in respiratory capacity due to impaired gill cell activity. This study has demonstrated that transparent goldfish can be used as a model for the toxicological analysis of various toxicants.