Yukinari Tsuruda

Effect of 17β-estradiol on the reproduction of Japanese medaka (Oryzias latipes)

Abstract Estrogenic compounds such as 17β-estradiol (E2) and its analogs are present in the aquatic environment and can adversely affect the reproductive systems of aquatic organisms. Although E2 has been detected at a maximum concentration of 64 ng/l in effluents of sewage treatment works (STWs), few reports address the associated effects on reproduction in fish. Therefore, we exposed adult medaka (Oryzias latipes) to mean measured E2 concentrations of 29.3, 55.7, 116, 227, and 463 ng/l for 21 d and assessed the effects on the egg number and fertility of paired medaka during the exposure period. In addition, we determined the hepatic vitellogenin (Vtg) concentration and histologically assessed the gonads of these fish. The number of egg produced and fertility of the paired medaka exposed to 463 ng/l E2 were significantly less compared with those of the control fish. Males in all treatment groups had developed testis–ova. Males treated with E2 concentrations=55.7 ng/l contained relating great concentrations of hepatic Vtg. Therefore, although only the greatest E2 concentration tested in our study affected fecundity and fertility, effects of E2 were observed on induction of Vtg and testis–ova in male medaka exposed to environmentally relevant concentrations of E2.

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 micrograms/L. Egg production of the pairs during the third week of exposure (15-21 d) was significantly decreased in the > or = 101-microgram/L treatment group, and fertility was significantly decreased in the 184-microgram/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-microgram/L treatment. The gonadosomatic index of the males in the 184-microgram/L group was also remarkably reduced. Hepatic vitellogenin (VTG) levels were significantly increased in both sexes receiving 4-NP treatments of > or = 50.9 micrograms/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 < or = 24.8 micrograms/L, respectively. The LOEC for reduced reproduction in medaka was at least four-fold greater than that required to elicit estogenic responses in male fish. Thus, we suggest that the estrogenic responses expressed in male fish are not responsible for the reduction in reproductive capacity.

The effects of methyltestosterone on the sexual development and reproduction of adult medaka (Oryzias latipes)

We examined the effects of methyltestosterone (MT) on the reproduction of medaka (Oryzias latipes). Six mating pairs of medaka were exposed for 3 weeks to MT at the measured concentrations of 22.5, 46.8, 88.1, 188, and 380 ng/L. The fecundity and fertility of paired medaka were significantly decreased in the 46.8, 88.1, 188, and 380 ng/L MT groups compared with those of controls. The gonadosomatic indices of female fish exposed to >or=46.8 ng/L were increased significantly. Gonadal histology showed degeneration of oocytes in the ovaries of fish in all MT treatment groups. Hepatic vitellogenin concentrations were significantly decreased in female fish treated with MT at 188 and 380 ng/L, and the hatchability and survival rate of the offspring were decreased in all MT treatment groups. These results clearly demonstrate that MT at >or=46.8 ng/L inhibited gonadal development and adversely affected the reproduction of medaka.

Recovery from reproductive and morphological abnormalities in medaka (Oryzias latipes) following a 14‐day exposure to diclofenac

Mating pairs of medaka (Oryzias latipes) were exposed to diclofenac at measured concentrations of 0 (control), 7.1, 37, and 78 μg/L for 14 d under static-renewal conditions. Effects on reproductive success, as well as morphological abnormalities, of the fish were assessed. During the exposure period, both fecundity and fertility were significantly decreased in the 37- and 78-μg/L treatment groups, and swollen abdomens in females were observed in all exposure groups. Notably, a defect of the lower jaw was also observed in 4 male fish: 2 at 37 μg/L and 2 at 78 μg/L of diclofenac. Subsequently, we investigated whether the reproductive and morphological abnormalities induced by diclofenac would be permanent or reversible once the medaka were returned to clean water. The reproductive ability of paired medaka was gradually restored to fish that were cultured in clean water for 14 d. After this period in clean water, we also observed a noticeable decrease in swollen abdomens in females; however, mandibular defects in the males remained, even after the 14-d recovery period. Radiographic and histochemical examinations revealed that diclofenac might affect bone remodeling in the lower jaw of male medaka because of a disruption in osteoclast function. These results suggest that reproductive impairments in pairs of medaka exposed to diclofenac may be reversible but that skeletal deformities (i.e., mandibular defect) in males may be persistent. Environ Toxicol Chem 2017;36:3277-3283.

Chronic exposure to diclofenac induces delayed mandibular defects in medaka (Oryzias latipes) in a sex-dependent manner

Diclofenac is widely distributed in freshwater environments. To support a robust aquatic risk assessment, medaka (Oryzias latipes) were exposed to diclofenac at sublethal concentrations of 0.608, 2.15, 7.29, 26.5, and 94.8 μg/L (as mean measured concentrations) from fertilized eggs to 90-day posthatch. Except for the induction of mandibular defects, no deleterious effects were observed on hatching success and time to hatching at the embryonic stage, or on posthatch mortality, growth in hatched larvae and juveniles, and no abnormal behavior was observed. After 40-day posthatch, mandibular defects in the fish were observed at a concentration of 7.29 μg/L and above. Cumulatively, a morphological examination showed that 4% of the fish in the 7.29 μg/L treatment, 20% in the 26.5 μg/L treatment, and 38% in the 94.8 μg/L treatment exhibited mandibular defects, and the sex ratio of fish with mandibular defects was skewed toward males. These results suggest that diclofenac affects bone remodeling in the lower jaw of medaka after puberty in a sex-dependent manner. The lowest observed-effect concentration and no observed-effect concentration of diclofenac for mandibular dysmorphism through the partial life cycle exposure of the medaka were 26.5 and 7.29 μg/L, respectively.