No overt reproductive impairment in zebrafish following life-cycle exposure to environmentally relevant...

Diphenyl phosphate (DPhP) is widely detected in environmental matrices, yet its reproductive toxicity following chronic exposure remains poorly understood. This study investigated the reproductive toxicity of life-cycle exposure to environmentally relevant concentrations of DPhP in zebrafish. Embryos (2 h post-fertilization) were exposed to DPhP at measured concentrations of 0.8, 3.9, or 35.6 μg/L for 120 days, covering the entire life cycle from embryo to adult. Reproductive endpoints assessed in adults included gonadosomatic index (GSI), gonad histopathology, reproductive performance, sex steroid hormone levels, expression of key genes along the hypothalamic-pituitary-gonadal (HPG) axis, and F₁ generation development. Exposure to 3.9 or 35.6 μg/L DPhP significantly increased GSI in females but not in males. Although no overt histopathological changes were detected in the gonads, females exposed to 35.6 μg/L DPhP showed a significant increase in the number of mature oocytes in the ovaries. Cumulative egg production over 21 days showed an increasing trend that did not reach statistical significance. In females, DPhP exposure significantly downregulated fshβ expression in the brain. However, at all tested concentrations, no significant changes were observed in other HPG axis-related genes or in plasma sex steroid hormone levels in either sex. Furthermore, no significant effects were found on hatching rate, survival rate, heart rate, or body length of F₁ offspring. Collectively, life-cycle exposure to DPhP within the tested concentration range exerts limited effects on the reproductive endocrine system of zebrafish and does not induce overt reproductive impairment.