Abstract
Vitellogenin (Vtg) is a female specific plasma protein and the major precursor of egg yolk protein in oviparous animals including fish and serves as a useful indicator of exposure of male or juvenile fish to estrogenic compounds. To assess possible estrogenic activity of effluent from sewage treatment works in Japan, we examined plasma Vtg concentration of juvenile Koi carp that were exposed in situ to the effluent by maintaining the fish in a cage deployed at a point downstream from the outfall of effluent. In the first trial with the juvenile fish (232 ± 99 g in body weight, n = 40) for 10 days, the exposure significantly (p < 0.01) increased the plasma Vtg concentration in the juvenile male group and the juvenile mixed-sex group. In the second trial with more and younger Koi carp (65 ± 23 g, n = 120) for 15 days, the effect of the exposure was more evident than in the first trial, with the statistical significance (p < 0.01) for each sex group. These results suggest that the effluent from a sewage treatment works had a weak but enough estrogenic activity to increase plasma Vtg levels of juvenile Koi carp. Chemical analyses for several compounds with estrogenic activity in the water samples at the exposure point suggest that natural estrogens, such as estradiol-17β and estrone, were possible candidate compounds responsible for the observed increase in the plasma Vtg levels.
