Microplastics Induced Dysfunctions in Physiology and Behavior of Fish: A Comprehensive Review

Microplastics (MPs) pollution is a global concern due to their widespread persistence, occurrence, and toxicity to aquatic organisms. Fish are most vulnerable to MPs due to their feeding habits and ecological niches. This review critically synthesizes current evidences on MPs induced disruptions of key physiological functions and behavioral patterns in fish, with an emphasis on the underlying mechanistic pathways and biological consequences. MPs originate from various sources, entering aquatic systems and being ingested by fish directly or via trophic transfer. A prominent effect is growth inhibition commonly caused by gastrointestinal damage, impaired nutrient absorption, and metabolic stress. Moreover, it causes several hematobiochemical disruptions including anemia, leukocyte fluctuations, and biochemical and enzymatic imbalances that are connected to oxidative stress and immunosuppression. MPs also disrupt reproductive performances of fish through altering gonadosomatic index, inducing endocrine disruptions, dysregulating hypothalamic-pituitary-gonadal axis genes, and reducing fertilization and hatching success, with several transgenerational effects. Furthermore, MPs can induce oxidative stress through overproduction of reactive oxygen species (ROS) and modulation of antioxidant enzymes, along with dysregulation of immune and inflammatory responses. Behavioral alterations include reduced swimming performance and changes in feeding and reproductive behavior, which are linked to neurotoxicity and impairment of energy metabolism. Although a limited number of studies suggest species-specific effects, most studies highlight significant adverse impacts on fish health. Hence, this review and meta-analysis indicates that MPs substantially compromise fish physiology manifesting as poor growth, altered blood and metabolic profiles, impaired reproduction, and behavioral patterns. By integrating sources and transport pathways to physiological and behavioral outcomes, this review provides a comprehensive summary to inform ecological risk assessment and management of MPs in fisheries and aquatic ecosystems.