Engineered nanoparticles and fish reproduction: Mechanistic pathways and environmental implications

The increasing production and environmental release of engineered nanoparticles (ENPs) have raised concerns regarding their impacts on aquatic organisms and ecosystem sustainability. We examine the environmental fate, transformation, bioavailability, and reproductive toxicity of ENPs in fish, focusing on silver, zinc oxide, titanium dioxide, copper oxide, and carbon-based nanomaterials. Current evidence indicates that ENPs impair reproduction through interconnected mechanisms involving oxidative stress, hypothalamic–pituitary–gonadal (HPG) axis disruption, apoptosis, autophagy, gonadal histopathology, and neuroendocrine dysfunction. Environmental processes such as aggregation, dissolution, and surface modification further influence nanoparticle bioavailability and toxicity, complicating ecological risk prediction. We propose an integrated mechanistic framework to explain how molecular and cellular disturbances translate into altered hormone regulation, impaired gametogenesis, reduced fertility, compromised offspring viability, and broader ecological consequences. Critical knowledge gaps include the mismatch between environmentally reported and experimentally applied concentrations, the scarcity of long-term and multigenerational studies, and the limited integration of omics-based findings with reproductive endpoints. Emerging evidence on life-stage sensitivity and mixture toxicity is also discussed. Finally, we outline future research and translational perspectives that emphasize environmentally realistic exposure scenarios, standardized testing strategies, adverse outcome pathway development, omics-driven investigations, and safer-by-design nanomaterials. This framework supports improved environmental risk assessment and the sustainable application of nanotechnology in aquatic ecosystems.