Chronic exposure to polystyrene nanoplastics induces gut damage and an altered feeding strategy, leading to insemination failure in male guppies.

Reproductive toxicity of nanoplastics is frequently attributed to endocrine disruption; however, whether gut injury and digestive dysfunction can cascade into terminal reproductive failure remains unclear. This study investigated the effects of chronic exposure to 70-nm polystyrene nanoplastics (PS-NPs; 0, 20, 200, and 2000 μg/L) on adult male guppies (Poecilia reticulata) over 90 days (approximately three reproductive cycles). Chronic PS-NP exposure induced significant intestinal histopathological damage (including villus shortening and epithelial vacuolization), reduced digestive enzyme activities, delayed defecation, and decreased body weight and Fulton's condition factor. Notably, exploratory foraging behavior was suppressed at high concentrations, whereas focused feeding increased, indicating a shift toward a relatively highly energy-conserving feeding strategy. However, this behavioral adaptation failed to compensate for the impaired nutrient acquisition, triggering an energy trade-off between survival and reproduction. Furthermore, diminished plasma cholesterol and whole-body testosterone levels were associated with disrupted spermatogenesis, reduced sperm velocity, and suppressed reproductive behavior. Consequently, insemination success declined from 100% in the control group to 89% at 200 μg/L, and eventually dropped to 0% at 2000 μg/L. These findings reveal a gut-origin cascade, wherein digestive dysfunction contributes to steroidogenic disruption and behavioral suppression, ultimately culminating in reproductive failure. These results highlight insemination success as a critical endpoint for comprehensively assessing the ecological risks of chronic nanoplastic exposure in aquatic organisms.