PARENT SESSION
PW2 - The Japanese Medaka Model
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P739) Effects of 4-nonylphenol on the reproduction of Japanese medaka (Oryzias latipes).
Kang, Ik Joon*,1, Yokota, Hirofumi2, Oshima, Yuji1, Tsuruda, Yukinari3, Hano, Takeshi1, Maeda, Masanobu2, Imada, Nobuyoshi1, Tadokoro, Hiroshi2, Honjo, Tsuneo1, 1 Division of Bioresource and Bioenvironmental Sciences, Kyushu University Graduate School, Fukuoka, Fukuoka, Japan2 Kurume Laboratory, Chemicals Evaluation and Research Institute, Japan (CERI), Kurume, Fukuoka, Japan3 Division of Animal and Marine Bioresource Science, Kyushu University Graduate School, Fukuoka, Fukuoka, Japan
ABSTRACT- We exposed mature Japanese medaka (Oryzias latipes) to 4-nonylphenol (4-NP) to elucidate its reproductive effects and estrogenic responses. For each treatment, 8 breeding pairs were exposed for 3 weeks at actual 4-NP concentrations of 24.8, 50.9, 101, and 184 
g/L. Egg production of the pairs during the 3rd week of exposure (15–21 days) was significantly decreased in the ≥ 101-g/L treatment group, and fertility was significantly decreased in the 184-g/L group. Induction of testis–ova was observed in male fish at all 4-NP concentrations, whereas abnormality of spermatogenesis was found only in those receiving the 184-g/L treatment. The gonadosomatic index of the males in the 184-g/L group was also remarkably reduced. Hepatic vitellogenin (VTG) levels were significantly increased in both sexes receiving 4-NP treatments of 50.9 g/L. Overall, the lowest observed effective concentrations (LOECs) of 4-NP for decreasing reproductive capacity (fecundity and fertility) and eliciting estrogenic responses (induction of testis–ova and VTG) were 101 and ≤24.8 g/L, respectively. The LOEC for reduced reproduction in medaka was at least 4-fold that required to elicit estrogenic responses in male fish, suggesting that the estrogenic responses expressed in male fish are not directly linked to the reduction in reproductive capacity.
Key words: 4-Nonylphenol, Medaka, Reproduction, Estrogenicity