Microplastic Pollution and Fish: Occurrence, Toxicological Mechanisms and Implications for Aquaculture and Human Health

Abstract: Microplastics, plastic particles smaller than 5 mm, are now among the most widespread contaminants of aquatic ecosystems, and fish positioned across all trophic levels, serve both as sentinels of this contamination and as a route through which it reaches human consumers. This chapter synthesises recent literature, with emphasis on work published between 2024 and 2026, on the occurrence of microplastics in fish across freshwater, marine and South Asian systems, their exposure pathways and tissue-specific accumulation, and their toxicological consequences at the organism, cellular and molecular level. Field surveys document widespread ingestion, with the gastrointestinal tract as the principal reservoir and secondary accumulation in gills, liver, muscle, heart and brain, and emerging evidence of trophic magnification in oceanic food webs. Toxicological evidence links exposure to intestinal and hepatic damage, gill hyperplasia, haematological and immune alterations, neurotoxicity, oxidative stress, gut dysbiosis and impaired growth and reproduction, with severity governed by particle size, polymer type, concentration and exposure duration rather than by exposure route alone. Early life stages are especially vulnerable, and the sub-100 nm fraction, nanoplastics, shows greater bioavailability and more systemic toxicity than microplastics. Microplastics further act as vectors for heavy metals, persistent organic pollutants, antibiotic resistance genes and pathogens, extending the hazard into food safety for the growing share of aquatic protein supplied by aquaculture, whose own infrastructure and feeds contribute to contamination. The chapter closes with detection and standardisation challenges, mitigation strategies spanning policy, technology and nutrition, and the research gaps that must be closed to protect fish populations, aquaculture productivity and consumer health.