Abstract
Microplastic pollution is of public concern for global environmental health, aquaculture, and fisheries. Toxicity studies have shown that microplastic ingestion may cause intestinal damage, microbiota dysbiosis, and disturb the lipid and energy metabolism in fish. To determine the impact of environmentally relevant, chronic, low dose microplastic fibers on fish health, medaka larvae, and juveniles were exposed to five concentrations of polyethylene (PE) fibers for 21 days through the feed. Fish growth and condition were assessed to determine the overall impact on fish health. To identify impaired energy intake, the gastrointestinal tract (GIT) integrity was evaluated at the molecular and cellular levels. Microbiota analysis was performed by comparing the top seven most abundant phyla present in both larval and juvenile fish exposed to 0, 1.5, and 3 PE fibers/fish/day. A shift in the phyla Proteobacteria and Bacteroidetes were observed. Larval samples demonstrated decreased proteobacteria abundance, while juvenile samples displayed an increase in abundance. Relative gene expression of key digestive genes from GIT tissue was quantified using real time-quantitative polymerase chain reaction. An effect on digestive gene expression potentially affecting nutrient absorption and antioxidant production was indicated via a significant decrease of solute carrier family 6 member 6 expression in larvae exposed to 6 fibers/fish/day. No significant molecular changes were observed in juvenile GIT tissue, although a non-monotonous dose-response was observed. GIT morphology was analyzed using histomorphological observations of the GIT mucus and cell types. No significant impairment of the GIT epithelial layers was observed in larvae or juveniles. To assess growth and condition, Fulton’s condition factor was measured. No differences were observed in larval or juvenile growth. Comparisons of different developmental stages allowed for identifying vulnerable developmental stages for microplastic exposure; larvae were more susceptible to molecular changes, while shifts in juvenile microbial communities were similar to changes reported post-polystyrene microplastic sphere exposure. This study is one of the first to provide toxicological data on the risk of PE fiber ingestion during fish development stages. Results indicate no imminent threat to fish condition at current measured environmental levels of microplastics; however, close monitoring of vital spawning grounds for commercially important fishes is recommended.
Highlights
Awareness of widespread plastic pollution in marine, freshwater, and terrestrial ecosystems is a worldwide environmental issue
Measurements of ISN, glucagon-like peptide 1 (GLP), peptide YY (PYY), and TRP failed to demonstrate any statistically significant difference at the studied concentrations. While these molecular markers, which are involved in glucose metabolism, energy homeostasis, weight gain, and proteolysis, were not differentially expressed in both age groups, the taurine membrane transporter slc6a6 was significantly downregulated in the larvae exposed to the highest microplastic concentration in this study, similar to changes seen in previous studies (Murashita et al, 2009; Polakof et al, 2011; Rønnestad et al, 2013)
This study examined the effect of microplastic ingestion on gene expression, gut microbiota, gastrointestinal tract (GIT) integrity, and fish growth and condition during two early life history stages
Summary
Awareness of widespread plastic pollution in marine, freshwater, and terrestrial ecosystems is a worldwide environmental issue. The location of microplastics in the aquatic environment depends on their chemical composition and density, which directly affects the potential of marine organisms’ exposure to these contaminants. Many different types of aquatic organisms, including teleost fish, mussels, and zooplankton, ingest microplastics inadvertently while feeding (Browne et al, 2008; Cole et al, 2013; Deudero and Alomar, 2015; Romeo et al, 2015; Granby et al, 2018). Various forms of physical damage in fish have been attributed to microplastic ingestion, such as intestinal lesions, dead tissue, and pro-inflammatory response (Ahrendt et al, 2020; Solomando et al, 2020; Zhang et al, 2020). Microplastic ingestion has been observed to affect digestive function, immune response, and microbiota dysbiosis (Huang et al, 2020). Metagenomic sequencing of the V4 region of the 16S rRNA gene will provide information on the taxonomic composition of the microbiota within medaka GITs (Costa and Weese, 2018)
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