Over the last century, plastics have been remarkable materials in peoples’ daily life due to its versatile, durable, and incredibly adaptable. Plastics production reached 368 million tonnes in 2019 worldwide with approximately 9% increasing rate every year and China contributed to 31% of world’s plastics production (Plastics Europe, 2020). In the meanwhile, the global total of plastic waste reached 380 Tg in 2018 with an exponential growth every year (Rai et al., 2021). Once entering the environment, plastic may degrade or fragment into microplastics through UV radiation, mechanical transformation or biological degradation by microorganisms (Cole et al., 2011; Alimi et al., 2018). Microplastics are small plastic pieces or fibers that are smaller than 5 mm in size (NOAA, 2015). They come in many forms, not only secondary sources, but also primary sources, such as microbeads found in personal care products (McDevitt et al., 2017). Microplastics contamination have been extensively reported in marine, freshwater and terrestrial ecosystems (Peng et al., 2020; Wang et al., 2020; Xu et al., 2020), thus identified as one of the top 10 emerging global environmental problems by the United Nations Environment Program.
Adverse effects of microplastics on fishes have been found in many literatures (Jacob et al., 2020; Abhijit et al.,2021; Anna et al.,2021). Due to the attractive color, buoyancy, and food-like properties, fish are particularly prone to ingesting microplastics (Garrido Gamarro et al., 2020). The ingestion of microplastics by fish can cause a variety of consequences: 1) microplastics can lead to physical damage and histopathological alterations (Peda et al., 2016; Jabeen et al., 2018; Ahrendt et al., 2020); 2) microplastics can cause impairments in oxidative, and disorders of inflammatory balance and intestinal microflora (Gu et al., 2020; Huang et al., 2020; Iheanacho and Odo, 2020); 3) microplastics can also lead to fish behavior changes (Brun et al., 2019; Guimarães et al., 2021; Rios-Fuster et al., 2021; Wei Shi et al., 2021); 4) microplastics can act as carriers to intensify further adverse effects of other pollutants on fish (Karami et al., 2016; Banaee et al., 2019; Zhang et al., 2019).
It is wildly acknowledged in the literatures that the ingestion, accumulation and elimination of microplastics in fishes are species-specific (Mizraji et al., 2017; Xu and Li, 2021), which was also verified with our previous studies (Wang et al., 2020; Zhang et al., 2021). Our field investigation found microplastic amounts in filter-feeding and omnivorous fish were higher than that of carnivorous species. Our laboratory experiment proved that microplastics ingestion in fish larvae was influenced by feeding type of fish, and omnivores fish were less able to eliminate microplastics than filter-feeding fish. An analysis of more than two thousand gut content surveys indicated that the largest plastic may ingest is about one-twentieth the length of the animal body length (Jams et al., 2020).
In this study, we will investigate species-specific effect of microplastics on three commercial fish species with different feeding types. Largemouth bass, Micropterus salmoides is a typical freshwater carnivorous fish species and widely farmed in China due to its strong adaptability, fast growth, delicious taste, and high economic value (Wang et al., 2020). Grass carp (Ctenopharyngodon idella), a herbivorous fish species, is one of the most important freshwater cultivars in China, which annual production exceeded 5.53 million tons in 2019 (China Fishery Statistical Yearbook, 2020). Jian carp (Cyprinus carpio var. Jian) is an omnivorous freshwater fish species with an annual production of 24.2 million tons worldwide (Yong Lin et al., 2019). This study aims to investigate the effects of microplastics on the morphology and inflammatory response in intestines of fishes with different feeding types. To achieve this goal, histopathological sections were examined, and immune-related genes profiles were used to study the changes in the intestinal tissue of three fishes after microplastics exposure. These results will provide a theoretical basis to further analysis of the mechanism of fish intestinal pathology caused by microplastics.