Determination of microplastic-mediated oxidative stress responses and DNA damage in economically important fish species in the largest dam lakes (Keban, Karakaya, and Atatürk) of Türkiye.

MP contamination and biomarkers were investigated in the economic importance fish species (Luciobarbus esocinus Heckel, 1843, Arabibarbus grypus Heckel, 1843 and Cyprinus carpio, Linnaeus, 1758). When MP content was considered, the highest MP concentration was found in the digestive system, followed by the gills, liver, and muscle tissue, respectively. Although regional and species-specific variations were observed in fish tissues, the predominant colors were blue and black, the predominant sizes were 151-500 µm and 501-3,000 µm, the predominant shapes were fragments and fibers, and the predominant polymer type was polyethylene. Significant interspecific differences were observed in microplastic (MP) accumulation. Arabibarbus grypus from the Atatürk Dam reservoir exhibited the highest burden (91 MP), nearly doubling the levels found in both Luciobarbus esocinus from the Karakaya Dam (47 MP) and Cyprinus carpio from the Keban Dam (46 MP). At the reservoir level, sediment and fish samples from Keban contained noticeably higher MP concentrations than those from Atatürk or Karakaya. In water, sediment, and fish samples collected on a regional basis, the Keban Dam has been identified as an area with a higher concentration of MP. While changes (increases/decreases) in the activities of antioxidant enzymes (SOD, CAT, and GPX) in gill and liver tissues were observed in fish from the Keban Dam, where MP levels were high; overall, increases were observed in MDA and ROS levels, as well as in the immunological parameters IL-6 and TNF-α, the DNA damage index 8-OHdG, and the apoptosis marker Caspase-3 levels (p < 0.05). The samples taken from the Keban Dam stood out as the region at highest risk, showing the highest levels of oxidative stress (ROS, MDA), DNA damage (8-OHdG), and apoptosis (Caspase-3) across all species compared to other regions. Among the species, Cyprinus carpio has been identified as the most sensitive to pollution, particularly based on the highest damage parameters recorded in the gill tissue at the Keban Dam. Overall, these results highlight that microplastics not only accumulate in fish tissues but also trigger biochemical defense mechanisms, and underscore their potential to cause non-lethal physiological stress in freshwater fish populations.