Suppression of male reproductive activity by estradiol in goldfish: appearance of infertile males that perform active spawning behavior

Estrogenic endocrine-disrupting chemicals are an increasing social concern, as they can reduce the reproductive activity of wildlife. The present study aimed to clarify the long-term effects of estradiol-17β (E2) on male reproductive activity in goldfish. Sexually mature male goldfish were implanted with a silicone capsule containing E2, and kept for 14 weeks or 15 weeks. The reproductive activity of these fish was individually traced. The percentage of fish with tubercles on opercula and pectoral fins and expressible milt started to decrease at 5 weeks after capsule implantation and remained at low levels. Inhibition of spawning activity by E2 occurred later than inhibition of the development of tubercles and milt production. Thirty percent of E2-treated fish showed no spawning at 15 weeks, whereas 70% of fish showed active spawning. The relationship between milt production and spawning activity revealed that some E2-treated fish performed active spawning behavior with no expressible milt because of the time lag of suppression between milt production and spawning activity. Therefore, environmental estrogen does not simply cause non-spawning males, but can also cause behaviorally active infertile males, which leads to failure of egg fertilization, resulting in a substantial decrease in population size in wild fish.