The Siberian sturgeon (Acipenser baerii) is a commercially-important fish. As it is the females that produce the highly-prized caviar, genetic monosex cultures would be valuable. Before such populations can be produced, it will first be necessary to formally confirm whether this species has a ZZ/ZW sex-determination system. This discovery will in turn require the development of successful sex inversion and progeny testing approaches. This work is a first step in advancing this strategy. Our aim was to induce gonadal transdifferentiation using two steroids found naturally in fish —estradiol-17β (E2) and 11β-hydroxyandrostenedione (11β-And)— to feminize and masculinize genetic males and females, respectively. Steroidal treatments were initiated at 3.5 months of age, using 5 μg/g body weight (b.w.) steroid injections; control fish received vehicle injections. Injections were given every 3 weeks for 7 months, concluding at 10.5 months. Genetic and histological tests were performed at 3.5, 6, 9, and 12 months of age. All animals remained histologically undifferentiated at 3.5 months. Control females showed signs of sex differentiation at 6 months (columnar epithelium with distinct folds), and at 9 and 12 months, control female and male gonads showed nests of oogonia and scattered spermatogonia, respectively. The E2 treatment induced male-to-female gonad transdifferentiation in the genetically-sexed males at 6, 9, and 12 months of age. In contrast, 11β-And failed to induce transdifferentiation of the female gonads. While some transient changes were observed, such as increased connective tissue between female germ cell clusters at 9 months, the 12-month-old fish displayed a normal female phenotype with no signs of sex inversion. Importantly, the experimental E2 treatment produced live phenotypic females transdifferentiated from genetic males, with normal growth, feeding, and mobility as compared with control fish. Further experiments are needed to attempt masculinization of females, potentially with higher doses of natural androgens or other hormones and chemicals.