|Budget Amount *help
¥3,500,000 (Direct Cost : ¥3,500,000)
Fiscal Year 1999 : ¥1,400,000 (Direct Cost : ¥1,400,000)
Fiscal Year 1998 : ¥2,100,000 (Direct Cost : ¥2,100,000)
Fish inhabiting coastal areas receiving agricultural, industrial, and domestic wastewaters have been exposed to various sublethal levels of environmental endocrine disruptors (EEDs) such as tributyltin (TBT), polychlorinated biphenyls (PCBs), or 17β-estradiol (E2). A decrease in reproductive success in fish collected from contaminated areas has been reported, and a reduction in spawning in fish exposed to EEDs has been observed. However, few studies have considered the combined effects of EEDs on the sexual behavior of fish. Therefore, we investigated the combined effects of EEDs on reproductive success and sexual behavior in Japanese medaka, Oryzias latipes.
Pairs of Japanese medaka were fed daily on diets containing TBT and PCBs (TBT+PCBs) : 1μg g-1 body weight per day) and E2 (3.30μg g-1 body weight per day), as a positive control, for 3 weeks. Reproductive success was measured by the number of eggs spawned and fertilization success. The sexual behavior of the males was assessed by p
airing them with a female injected with prostaglandin, which is known to stimulate sexual behavior in male medaka. The behavior of the fish was recorded by video camera for one hour and analyzed for frequencies of typical sexual behaviors (following, courting dance, and crossing) performed toward the female.
A significant reduction in the number of eggs spawned and fertilization success was observed in those treated with TBT+PCBs and with E2, when compared with negative controls. Furthermore, the sexual behavior of treated males was suppressed compared to that of the control fish, although no change was observed in the normal swimming speed of the treated males. These data show that impairment of sexual behavior is caused by endocrine disruption, and that this disruption is one of the causes of reduced spawning in medaka treated with TBT+PCBs. Accordingly, a reproductive assay that includes sexual behavior of medaka might be highly useful for detecting endocrine dysfunction, especially as induced by a combination of EEDs.
In another experiment, TBT (2μg/shell) was injected to pearl oyster shell. After injection, tissues (mid-gut gland, gonad, muscle, etc) were collected and subjected to the determination of TBT. As a results, high concentration were observed in mid-gut gland and gonad. Thus, TBT might be accumulated in shell and affected its reproduction. Less