Microplastics affect food intake and the expression of appetite regulators and nutrient transporters in pond loach (Misgurnus anguillicaudatus)

Microplastics (MPs) are emerging pollutants in freshwater ecosystems, posing risks to aquatic organisms. This study examines the effects of dietary MP exposure on food intake, appetite regulation, and nutrient transporter expression in pond loach (Misgurnus anguillicaudatus), a sediment-feeding facultative air breathing freshwater fish. Fish were exposed to small (250-300 μm), medium (425-500 μm), and large (710-850 μm) polyethylene microspheres for two weeks. Food intake was significantly reduced in fish fed small and medium MPs, but not large MPs, suggesting size-dependent ingestion effects. In the brain, MP (425-500 μm) exposure suppressed orexin expression, a key appetite-stimulating neuropeptide, while other central appetite regulators remained unchanged. In the anterior intestine, anorexigenic peptides such as cholecystokinin (cck) and peptide YY (pyy) were upregulated, alongside glucose-dependent insulinotropic polypeptide (gip), indicating enhanced satiety signaling. Sodium-dependent glucose transporter 1 (slc5a1) expression was downregulated, suggesting impaired glucose absorption. MPs induced upregulation of gip and urea transporter 2 (slc14a2) in the mid intestine, and pyy, gip, glucose transporter 1 (slc2a1), urea transporter 2 and hypoxia-inducible factor 1α (hif1a) in the posterior intestine. These results show that MP exposure disrupts feeding, alters endocrine signaling, and affects nutrient absorption in pond loach, highlighting the physiological sensitivity of sediment-feeding fish to MP contamination and the ecological risks posed by plastic pollution to aquatic species and ecosystems.