Abstract
Plasma vitellogenin concentration was measured in wild carp captured from Lake Kojima in Okayama Prefecture at monthly intervals over a five-year period. Calculation of the gonadosomatic index (GSI), calculated as gonad-weight/body-weight, and revealed that reproductive development in males and females was seasonally synchronized. Similarly, seasonal changes in the vitellogenin concentration of male carp plasma were similar to the GSI of not only male carp but also female carp except during the breeding season. Since seasonal variations of 17β-estradiol and bisphenol A were not apparent, it is proposed that the vitellogenin concentration in male carp plasma changed relative to the stage of sexual maturity of the carp. Vitellogenin concentrations exceeding 1000 ng/ml in male carp plasma accounted for 1.9% of 210 specimens. The findings showed that the carp inhabiting Lake Kojima do not appear to be affected by estrogen-like substances at present.
