Fish full life‐cycle testing for androgen methyltestosterone on medaka (Oryzias latipes)

Abstract

Abstract-We studied the chronic effects of methyltestosterone (MT) on reproductive status of medaka (Oryzias latipes) over two generations under continuous exposure to verify the applicability of the fish full life-cycle test (FFLC) for this androgen with this species. The exposure of parental (F0) medaka to MT was begun on embryos within 12 h postfertilization and continued for up to 101 d; assessment endpoints included embryological development, hatching, posthatch survival, growth, sexual differentiation, reproduction, and hepatic vitellogenin (VTG) levels under flow-through exposure to MT at each mean measured concentration of 0.35, 1.09, 3.29, 9.98, and 27.75 ng/L. Eggs (F1) spawned from the F0 fish at 98, 99, and 100 d posthatch were examined for hatchability, survival after hatching, growth, sexual differentiation, and hepatic VTG level until 60 d posthatch. In the FFLC with medaka, MT induced masculinization of both secondary sex characteristics and gonads. We observed that all F0 fish in the 27.75-ng/L treatment group showed male secondary sex characteristics in which no fish with ovary could be discerned. Several fish with ovaries in F0 and F1 generations treated with 9.98 ng/L showed male secondary sex characteristics. We also observed swollen abdomens in the F0 and F1 female fish in the 9.98-ng/L treatment group. These swollen abdomens were induced by enlarged ovaries and were accompanied with declined fecundity and fertility in the F0 generation. These results indicate that MT reduces the reproductive potential of medaka and that the FFLC with this species is applicable to the evaluation of androgens.

Exposure of three generations of the estuarine sheepshead minnow (Cyprinodon variegatus) to the androgen, 17β‐trenbolone: Effects on survival, development, and reproduction

“…Exposures of freshwater fish to EDCs that include an entire life cycle have demonstrated increased sensitivity of subsequent generations measured by fecundity and survival of zebrafish [30], and changes of hepatic vitellogenin and incidence of testisova in medaka [11,31,32]. Multiple-generation exposures of sheepshead minnow to Tb in the present study and to 17b-estradiol [4,5] have demonstrated that in some cases, short-term adult exposures may not effectively predict the impacts on continuously exposed populations.…”

“…Trenbolone produced ovotestes in all female mosquitofish fry that were reared in water containing 1.0 or 10 mg/L [27]. Exposure to the androgen methyltestosterone produced a dose-related increase in similarly degenerated oocytes in medaka [28] and 3 of 20 medaka exposed to 27.75 ng/L exhibited testis-ova gonads [11]. In the present study, atypical ovaries and/or intersex occurred in the F1 generation exposed to only the 0.13 and 0.87 mg Tb/L treatments and was accompanied by significantly reduced reproduction, increased numbers of abnormal embryos and infertile eggs, and reduced hatch of offspring.…”

“…To date, most androgen effects on fish have been evaluated using short-term ( 21-d) trenbolone exposures measuring fecundity, gene expression, morphology, gonadosomatic index, vitellogenin and plasma steroid changes, and protein biomarkers [6][7][8][9][10]. An exception is the study by Seki et al [11], in which medaka (Oryzias latipes) exposed to the androgen, methyl testosterone, through a full life cycle to 60-d posthatch (dph) of the F1 generation had altered secondary sex characteristics (F0), gonadal histology (F0), and hepatic vitellogenin levels (F1). The impacts of the androgen, 17b-trenbolone (Tb), on reproduction as well as survival and development of fish exposed for multiple generations are still undetermined.…”

Effects of pentachlorophenol on the reproduction of Japanese medaka (Oryzias latipes)

“…When adult medaka exposed to 20 g/l of TCS, hatching rates of the offspring (F1) decreased significantly [12]. In addition, hatching rates and time to hatch of offspring of medaka exposure to androgen methyltestosterone was significantly less than that of the control [44].…”

Detailed Review Paper on Fish Screening Assays for the Detection of Endocrine Active Substances

“…number of nuptial tubercles in fathead minnow, number of papillary processes in medaka). Quantitative analysis can be performed on semi-empirical observations of secondary sex attributes in chemically exposed fish Seki et al, 2004). An excellent example is provided by Papoulias et al (2000), who used a readily available statistical software package (SPSS, Chicago IL) to perform stepwise discriminant analysis to assess the predictability of secondary sex characteristics in identifying genotypic sex in the medaka.…”