Effects of 4-nonylphenol on reproduction of Japanese medaka, Oryzias latipes

We exposed mature Japanese medaka (Oryzias latipes) to 4-nonylphenol (4-NP) to elucidate its reproductive effects and estrogenic responses. For each treatment, eight breeding pairs were exposed for 3 weeks at measured 4-NP concentrations of 24.8, 50.9, 101, and 184 μg/L. Egg production of the pairs during the third week of exposure (15-21 d) was significantly decreased in the ≥101-μg/L treatment group, and fertility was significantly decreased in the 184-μg/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-μg/L treatment. The gonadosomatic index of the males in the 184-μg/L group was also remarkably reduced. Hepatic vitellogenin (VTG) levels were significantly increased in both sexes receiving 4-NP treatments of ≥50.9 μg/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 μg/L, respectively. The LOEC for reduced reproduction in medaka was at least four-fold greater than that required to elicit estrogenic responses in male fish. Thus, we suggest that the estrogenic responses expressed in male fish are not responsible for the reduction in reproductive capacity.