Trophic transfer of nanoplastics reduces larval survival of marine fish more than waterborne exposure

Microplastics (MPs) and nanoplastics (NPs) are widespread contaminants in marine environments and pose significant risks to aquatic organisms. However, physiological effects and survival consequences of different MP and NP exposure pathways during early developmental stages of marine fish remain poorly understood. We investigated effects of direct and indirect consumption of MPs and NPs by larvae of red sea bream (Pagrus major) using a controlled laboratory system. Larvae were exposed to fluorescently labeled polystyrene particles (3 μm and 0.2 μm) either directly from the water or indirectly via contaminated zooplankton prey. MPs and NPs were detected in digestive tracts of all exposed individuals, regardless of the exposure route. However, survival was significantly reduced in larvae that consumed NPs via rotifer predation, suggesting that ingestion of contaminated prey organisms may represent a greater hazard than direct uptake from water. In both groups, antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) were elevated, suggesting induction of oxidative stress. Relative gene expression revealed greater upregulation of several stress and immune-related genes in larvae exposed to MPs via rotifer predation than via direct consumption. Our findings provide clear evidence that both MPs and NPs can alter physiological and molecular responses in marine fish larvae, especially via rotifer predation. This study suggests the importance of considering trophic interactions in ecotoxicological assessments of plastic pollution to address plastic bioavailability and toxicity during early life stages.