Feminisation of young males of the common carp, Cyprinus carpio, exposed to 4- tert-pentylphenol during sexual differentiation

In recent years, a hierarchy of techniques has become available for detecting chemicals which may cause endocrine disruption in the aquatic environment. The molecular structure of a chemical provides a first indication about estrogenic activity, i.e. their likelihood of interfering with the female hormone receptor. In vitro competitive binding assays for this receptor and specific cell cultures are also used to demonstrate an estrogenic response, but this does not adequately indicate whether the substance will cause adverse reproductive effects in an entire organism. An elevated level of vitellogenin, a typical female lipoprotein in the plasma of male fish is an in vivo estrogen-mediated response. However, its direct relationship to reproductive developmental effects is as yet unclear. The present study aims at investigating this relationship for assessing endocrine disruption in fish exposed to an estrogenic substance during relevant life stages. A monosex population of male carp, Cyprinus carpio, was exposed to 4-tert-pentylphenol (TPP) and to 17 β-estradiol as a positive control during the period of sexual differentiation, starting at 50 days post hatch. The fish were sampled every 10 days for the histological examination of the development of the testes, i.e. the formation of the reproductive tract, the multiplication and subsequent meiosis of the primordial germ cells, and gametogenesis in the early gonad. At the end of the experiment, blood was extracted for the quantification of vitellogenin by radioimmunoassays in the plasma. The average number of primordial germ cells (PGCs) per gonadal section was significantly reduced ( P