Keywords: 
• polychlorinated biphenyl (PCBs) /
• Gambusia affinis /
• CYP19α /
• VTGα /
• mRNA expression /
• hemal spine /
• morphological masculinization

Abstract: The cytochrome P450 aromatase (CYP19α) and vitellogenin (VTGα) genes mRNA transcriptional levels in mosquitofish (Gambusia affinis) were detected in order to investigate the effects of trace PCBs on the CYP19α and VTGα expression in the adult female G. affinis for long time exposure, and evaluate its effect on the morphological masculinization in female G. affinis. G. affinis were randomly divided into five groups, with one control group and four experimental groups (0.08, 0.4, 2 and 10 µg·L^-1 PCBs). Parallel experimental groups were also established. The CYP19α and VTGα mRNA expression levels in fish gonad and liver tissues were determined after 14 and 28 d exposure, respectively. The effect of PCBs on the development of hemal spine was also detected. The exposure experiment results showed that:① different concentrations of PCBs group (0.08, 0.4, 2 and 10 µg·L^-1 PCBs) exposure could inhibit the G. affinis CYP19α and VTGα gene expression, which suggested that the inhibition of PCBs on G. affinis VTGα gene was far greater than the inhibition of G. affinis CYP19α gene; ② 0.4 µg·L^-1 PCBs exposure significantly reduced the length (L) of 15th haemal spine, and reduced the L/D ratio of 15th and 16th haemal spine in G. affinis, which appeared masculinization of skeletal morphology. These showed that a certain concentration of PCBs exposure would show anti estrogen effect.