Gill dysfunction and metabolic disruption: the size-dependent effects of microplastics on Chiromantes haematocheir

Plastic particles are emerging aquatic pollutants, but their size-associated effects on crab gill toxicity remain unclear. In this study, Chiromantes haematocheir was exposed to polystyrene particles of 75 nm, 500 nm, and 1000 nm for 21 days to evaluate gill accumulation, oxidative stress, immune response, energy metabolism, and apoptosis. Polystyrene particles accumulated in the gills and induced tissue injury and apoptotic cell death, with PS75 causing the most severe damage. Biochemical assays showed that PS exposure disturbed glycolytic enzyme activities, antioxidant defence, and immune-related indicators. Transcriptomic analysis further revealed that different particle sizes affected pathways related to glycolysis, oxidative phosphorylation, mitochondrial electron transport, antioxidant response, immune regulation, and apoptosis. PS75 induced the strongest metabolic reprogramming, oxidative stress, and apoptotic activation, whereas PS1000 showed stronger compensatory antioxidant and mitochondrial responses. Overall, these results indicate that polystyrene particles induce size-associated gill toxicity in C. haematocheir, with smaller particles causing greater physiological and molecular disruption.