Early-life phenanthrene exposure inhibits reproductive ability in adult zebrafish and the mechanism of action.

Phenanthrene (Phe) is a representative polycyclic aromatic hydrocarbon, and its ubiquity makes the risk assessment of Phe in aquatic ecosystems important. To assess the long-term effects of early-life Phe exposure on fish, the embryos of the model organism, zrbrafish (Danio rerio) were exposed to Phe at 0.05, 0.5, 5 and 50 nmol/L for 96 h and then raised to adulthood in clean water. Gonad development and reproductive functions were investigated in 120 day-old fish. The results showed that the percentage of spermatozoa in males and mature oocytes in females were decreased. The spawned egg numbers and the fertilization rate were reduced when the treated fish were mated with untreated fish. The transcription of genes involved in the brain-pituitary-gonadal axis was downregulated. The levels of both 17β-estradiol and testosterone were significantly decreased in the 5 and 50 nmol/L groups compared with the control group. The methylation levels in the promotor of gnrh3 (encoding gonadotropin releasing hormone) were significantly elevated in the adult fish in the 5 and 50 nmol/L treatments, which might be associated with the downregulation of gnrh3 transcription. These results suggested that embryonic exposure to Phe can inhibit the reproductive ability of adult fish, which should be adequately emphasized in its risk assessment.