Distribution characteristics of microplastics in fish of the Tibetan plateau and its physiological effects on Schizothorax davidi

Microplastic (MP) pollution in aquatic organisms poses a critical threat to aquatic ecosystem health and human food safety, however, the MP abundance, composition, and toxicological effects in cold fish from the Tibetan Plateau remain poorly understood. Microplastic pollution has emerged as a potential ecological threat to native fish species inhabiting the Tibetan Plateau. Field surveys revealed widespread MP ingestion, with a higher occurrence in farmed fish (61.9 %, 1.50-3.88 MPs/individual) compared to wild populations (44.4 %, 1.33-7.60 MPs/individual). The 30-day exposure experiment revealed dose-dependent PS-MPs accumulation in S. davidi (up to 1.37 μg/mg), accompanied by oxidative stress responses. Although glutathione levels increased as a compensatory defense, lipid peroxidation occurred at the highest exposure concentration (250 μg/L), with malondialdehyde levels reaching 2.1-fold of controls. Physical swimming ability was reduced, with a 45 % increase in induced velocity and a 37 % reduction in critical swimming speed. Chronic PS-MPs exposure also caused pronounced dysbiosis of gut microbiota, including a 5267 % proliferation of Cetobacterium and resurgence of pathogenic Aeromonas. Collectively, these effects resulted in a 28-37 % decline in migratory swimming capacity and multiple physiological disruptions. The results indicated that PS-MPs induced the oxidative stress, neurobehavioral impairment, and gut microbial imbalance, thereby threatening the survival and migratory fitness of Tibetan Plateau fish.