Microplastic pollution has become a major global concern. Coastal areas are densely populated with human activity, commercial enterprises, and fishing, resulting in high incidences of fish microplastic pollution. It has been shown that microplastics exist in commercial fish in coastal areas of Guangdong, China. Most of the microplastics were less than 1 mm, white and blue fibers. The abundance, type, shape and color of microplastics in gills and in the gastrointestinal tract (GIT) of eight species of commercial fish in the coastal waters of central and western Guangdong Province were analyzed. The overall abundance of microplastic particles in fish was 6.6 items/individual, with an average of 2.2 particles in gills and 4.4 in the GIT. The GIT of carnivorous fish was less likely to ingest microplastics than that of herbivores or omnivores. Middle-water fish, on the other hand, are less likely to have their gills contaminated with microplastics. These results revealed the degree of microplastic pollution in fish tissues from the central and western coastal areas of Guangdong province. The quantity of microplastics in the GIT of fish in the Pearl River Delta was the highest compared with the surrounding areas.

Microplastics have caused great concern in recent years. However, few studies have compared the toxicity of different sizes of microplastics in fishes, especially commercial fishes, which are more related to human health. In the present study, we revealed the effects of varying sizes of microplastics on grass carp embryos and larvae using scanning electron microscopy (SEM) and fluorescence imaging. Embryos were exposed to 80 nm and 8 μm microplastics at concentrations of 5, 15, and 45 mg/L. Toxicity kinetics of various sizes of fluorescent microplastics were analyzed through microscopic observation in the larvae. Results found that nanoplastics could not penetrate the embryo’s chorionic membrane, instead they conglutinated or aggregated on the chorion. Our results are the first to explore the defense mechanisms of commercial fish embryos against microplastics. Larvae were prone to ingesting their own excrement, resulting in microplastic flocculants winding around their mouth. For the first time, it was found that excreted microplastics could be reconsumed by fish and reaccumulated in the oral cavity. Microplastics of a certain size (1 μm) could be accumulated in the nasal cavity. We speculate that the presence of a special groove structure in the nasal cavity of grass carp larvae may manage to seize the microplastics with a particular size. As far as we know, this is the first report of microplastics being found in the nasal passages of fish. Fluorescence images clearly recorded the toxicity kinetics of microplastics in herbivorous fish.

Microplastics, which are defined as small plastic particles smaller than 5 mm, have been found in various aquatic environments all over the world. In this study, we investigated the level of microplastics in the surface water and estuarine mullet Mugil cephalus from 23 estuary areas in the south of China. M. cephalus, due to its wide distribution and high tolerance, was selected as a candidate fish species for monitoring the ingestion of marine microplastics. The size, color, and type of all microplastics were recorded from the water and fish samples by stereomicroscope. The average abundance of microplastics was 18,261 items/m³ in the surface water, and 7.2 items/individual in fish. These alarming numbers revealed significant pollution due to microplastics in the environment. Fragments and minute-sized particles were the most common features found in both the water and the fish samples. Some impurities in the water sample were easily confused with microplastics, but regular forms on the surface of the impurity could be distinguished by using scanning electron microscopy (SEM). The shape, color, and size of the microplastics in the fish and water samples were similar, which suggested that the microplastics in the water might enter the organisms’ body, thereby affecting the health of aquatic species and even humans. Based on these findings, it is highly recommended that the monitoring and managing of pollution due to microplastics be addressed in the estuaries.