Comparison of serum vitellogenin, steroid hormone, gonad histopathology and bioaccumulation in common carp (Cyprinus carpio) of two rivers and a lake in Japan: potential for endocrine disruption.

To investigate endocrine disruption and chemical contaminant levels in the aquatic environment, serum vitellogenin (Vtg) induction, steroid hormone synthesis, gonad histopathology and nonylphenol (NP) bioaccumulation were measured in common carp (Cyprinus carpio) in three sites (two rivers and one lake, in which high, medium, and low NP concentrations were detected in a previous study) in Japan from November 2001 to February 2002. The average gonadosomatic indexes (GSIs) for males were 3.9% in the Ishizu River, 5.6% in the Imba discharge channel, and 4.2% in Teganuma. No testis-ova in the gonads were found in any of the captured carp in this study. Abnormalities in testis were observed in individuals (n = 2/15) captured in the Imba discharge channel, and retraction and unusual cell proliferation were observed in the testis of the same fish. Serum Vtg was detected in 40% of the male samples captured in the Ishizu River and in 53% of the male samples captured in the Imba discharge channel. The levels of alkylphenols and bisphenol A, as well as estrogenic activity, were determined in the aquatic environment. In additional caging experiments in the Nikko River (medium NP concentration), male carp showed NP bioconcentration after the exposure to the river water.