Embryonic exposure to the WAF of crude oil impairs male Oryzias melastigma reproduction and the mechanism involved

The occurrence of marine oil spill poses a severe threat to the health of marine species. Early life stage of marine fish is particularly vulnerable to the water-accommodated fraction (WAF) of crude oil. However, the impact of embryonic exposure to the WAF on reproductive ability in male adult marine fish is unknown. In this study, fertilized Oryzias melastigma embryos were exposed to 0.5, 5, 50 and 500 μg/L of total petroleum hydrocarbon in the WAF for 7 days, and then the embryos were raised to 130 days post-fertilization. Subsequently, the reproductive toxicity and mechanism involved in male O. melastigma adults was investigated. Our results revealed a reduction in fecundity in F0 male O. melastigma adults. Additionally, the F1 unexposed larvae had a much higher death rate, much worse fertilization success, and a very poor hatching rate. In F0 male adults, the gonadosomatic index and sperm percentage were significantly reduced, along with a marked decrease in testosterone levels. Embryonic WAF exposure significantly altered hypothalamic-pituitary-gonadal-liver (HPGL) axis-associated gene expression: sGnRH, GnRHr2, LHβ, CYP19B, ERα/β, ARα/β, and VTG. Furthermore, GnRHr2 and LHβ methylation levels were elevated in the adult brain, potentially suppressing their expression. This epigenetic modification resulting from embryonic WAF exposure may underlie the observed physiological alterations along the HPGL axis. These findings indicate that embryonic WAF exposure can induce male-specific reproductive impairment in marine fish, highlighting the need for developing more targeted strategies on risk assessment.