Reversibility of estrogenic sex changes in zebrafish (Danio rerio).

Development of male zebrafish (Danio rerio) courtship behavior was studied following estrogenic disruption of sexual differentiation. Sixty zebrafish were exposed at 28 degrees C to 5 ng/L (nominal concentration) of 17alpha-ethinylestradiol (EE2) from the egg stage until adulthood at four months of age, resulting in a female-biased sex ratio. Twenty-five EE2-exposed phenotypic female zebrafish were subsequently held in clean water for eight months. During this period, eight phenotypic males developed. These phenotypic males demonstrated significant behavioral aberrations and a low fertilization rate compared to control males.