Trenbolone acetate metabolites promote ovarian growth and development in adult Japanese medaka (Oryzias latipes)

• Medaka exposed to trenbolone acetate metabolites had altered ovarian composition.
• 17α-Trenbolone significantly increased 17β-estradiol (pg/mg).
• Trendione significantly decreased whole body 17β-estradiol and testosterone (pg/mg).
• Trenbolone acetate metabolites were found to have estrogenic potential.

Trenbolone acetate, a synthetic androgen, has been used as a growth promoter in beef cattle in the US since 1987. While several teleost studies have investigated the masculinization effects of the metabolite 17β-trenbolone, few have focused on the reproductive impacts of all three trenbolone acetate (TBA) metabolites including trendione. Adult female medaka (Oryzias latipes) were exposed to TBA metabolites (10, 100, and 1000 ng/L) for 14 days (n = 3). Histological examination revealed that TBA metabolites (1000 ng/L) significantly reduced the percentage of primary ovarian follicles and increased the percentage of vitellogenic follicles compared to control fish. 17α-Trenbolone significantly increased whereas trendione reduced whole body levels of estradiol-17β. Testosterone was significantly reduced by trendione treatment and only the highest dose of 17β-trenbolone and lowest dose of trendione altered 11-ketotestosterone. Additionally, TBA metabolites may be further broken down and/or metabolized or converted by the animal influencing both sex steroid levels and ovarian development.