Effects of long-term nonylphenol exposure on gonadal development and biomarkers of estrogenicity in juvenile rainbow trout Oncorhynchus mykiss.

Environmental pollutants with estrogenic activity including nonylphenol (NP) have the potential to alter gonadal development and reproduction of wild fish. To investigate the estrogenic action of environmentally relevant concentrations of NP, rainbow trout (Oncorhynchus mykiss) were continuously exposed during the embryonic, larval and juvenile life stage to 1.05 and 10.17 microg/l NP for 1 year, and sexual differentiation, vitellogenin (VG), VG mRNA, and zona radiata protein (ZRP) expression were examined after that period. The applied NP concentrations did not affect mortality and hatching rates, and did not have an influence on the body weight of 1-year-old fish. No occurrence of testis-ova was observed and sex-ratios of NP exposed groups of fish were unchanged when compared with control groups. The induction of VG and ZRP expression was a more sensitive reaction to the presence of NP than the formation of testis-ova and the reversal of sex. Increased VG expression in trout liver occurred already at 1.05 microg/l NP, whereas VG mRNA levels, quantified by competitive RT-PCR, were not significantly elevated in NP exposed fish. ZRP contents were significantly higher at 10.17 microg/l NP. Since induction of VG did not occur in all fish exposed to 1 or 10 microg/l NP and ZRP induction did not occur in all fish exposed to 10 microg/l, some individuals may be more affected by exposure to NP than others. This study demonstrates that NP concentrations typically found in sewage treatment effluents and some rivers do not affect sexual differentiation in rainbow trout, but induce VG and ZRP expression in the liver of exposed fish.