Minimum oral dose of genistein required to feminize sterlet (Acipenser ruthenus) evaluated based on oocyte appearance in the testes

Induction of gonad development into ovaries in genetic male sterlets ( Acipenser ruthenus ) has previously been achieved by dietary supplementation with 1000 μg/g genistein (GS), a phytoestrogen. The present study aimed to determine the lowest effective GS dose capable of feminizing genetic male sterlets. Genetically male sterlets at 137 days post-hatch (DPH) were divided into four groups of 30 individuals (53.9 ± 1.87 g), orally administered GS at doses of 0, 500, 800, and 1000 μg/g diet for 180 days in in the group tanks with flow-through river water, and then fed a GS-free diet for approximately 200 days prior to sampling. The results revealed that GS did not affect survival or growth rates. Intersex gonads were observed in 15/25, 22/25, and 20/24 fish in the 0, 500, 800, and 1000 μg/g dietary GS groups, respectively, and the minimum GS dose required to induce ovarian tissue development in the testis was ≤500 μg/g diet. Furthermore, a novel classification system for ovarian tissue development within the testes was introduced that consists of stages 0 to 4 based on the histological analysis results. A significant correlation was observed between GS dose and gonadal stage (ordinal logistic regression analysis: p < 0.05, R 2 = 0.279), suggesting that GS increased the proportion of gonadal ovarian tissue in a dose-dependent manner. The results of this study suggest that administering an appropriate GS dosage could contribute towards the development of formulated feed that induces feminization in farmed sterlet. • Lowest effective genistein dose for feminizing genetic male sterlet was assessed. • The minimum genistein dose required to induce feminization was ≤500 μg/g diet. • Genistein at 1000 μg/g fed to 137 DPH starlets for 6 months led to incomplete feminization. • Genistein did not affect survival or growth rates.