MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(GRE-1117-748577) Effect of the estrogen mimic genistein on sex differentiation and EROD activity in channel catfish.

Green, C¹, Kelly, A¹, ¹ Fisheries and Illinois Aquaculture Center, Southern Illinois University, Carbondale, IL, USA

ABSTRACT- Several chemicals present in aquatic environments are known to serve as endocrine disruptors by mimicking or antagonizing the actions of steroid hormones. In fish, one consequence of endocrine disruption maybe an alteration in phenotypic sex differentiation. Soybean meal, proposed as an alternative protein source in aquaculture feeds, contain significant levels of the phytoestrogen genistein, which mimics estrogen activity. Channel catfish (Ictalurus punctatus) were fed four dietary concentrations of the phytoestrogen genistein (0, 2, 4, and 8 mg/g) to determine its effect on gonadal sex differentiation. Additionally, the relation between ethoxyresorufin-O-deethylase (EROD) activity and chronic exposure to dietary phytoestrogens during sexual differentiation was examined. The four treatment diets were fed to sexually undifferentiated channel catfish between 30 and 150 days of age. Phenotypic sex was determined by histological examination of the gonads. Phenotypic sex was significantly dependant on dietary phytoestrogen concentration (p = 0.014). Additionally, logistic regression showed a significant relation between genistein concentration in the diet and gonadal sex (p = 0.038). Intersex individuals and greater number of male phenotypes were present in the 4 and 8 mg/g treatment groups. No significant differences in EROD activity among treatments and control were observed during or after dietary exposure. These findings establish that relevant dietary concentrations of genistein could alter sex ratios in cultured channel catfish populations, and demonstrate the uncertainty of EROD activity as a biomarker of chronic exposure to phytoestrogens.

Key words: phytoestrogens, EROD, sex differentiation, endocrine disruption