Chronic triphenyl phosphate exposure disrupts HPG axis and impairs reproduction in marine medaka (Oryzias melastigma)

Triphenyl phosphate (TPhP), a widely used organophosphorus flame retardant, has become a typical emerging pollutant in marine environments, yet its toxicity in marine fish is far from conclusive. This study investigated the chronic reproductive toxicity of TPhP in marine medaka ( Oryzias melastigma ) at environmentally relevant concentrations (1.514–10.804 μg/L). After 90-day exposure, the hypothalamus-pituitary-gonad (HPG) axis was obviously disrupted. In the brain, the expression of gonadotropin-releasing hormone (GnRH) and gonadotropin hormone (GtH) related genes was dysregulated. A hormetic manner, with an increase at the low concentration but a decrease up to 40% at higher concentrations, was observed in the expression of cgα, fshβ and lhβ . Females exhibited reduced GSI (5.4–25.4% decline) and egg production, alongside downregulated estrogen-related genes (e.g., cyp19a, 17β-hsd, erα, erβ ) in liver and ovary. Males showed molecular and morphological disordered spermatogenesis, with increased type B spermatogonia but decreased spermatocytes and spermatids, indicating a decrease of mature spermatozoa. These findings underscore the endocrine-disrupting effects of TPhP and its potential threat on the reproductive continuity of marine fish populations. Given its high detection frequency and environmental residual concentration in coastal areas, further large-scale investigations and regulatory policy development are warranted.