Gonadal sex differentiation in teleost fish shows greater plasticity as compared to other vertebrates, as it can be influenced by a variety of factors such as exogenous sex steroids. Exogenous estrogens, such as 17β-estradiol (E2), can induce feminization when administered during early embryonic development. However, the mechanisms underlying the E2-induced feminization are not fully understood, especially in Neotropical species. Therefore, the aim of this study was to evaluate the effects of E2 administration on the phenotypic sex characteristics, histological assessment of the gonads, and the expression of selected genes in Astyanax altiparanae exposed to dietary E2 prior to gonadal differentiation. At 4 days post-hatch (dph), groups of 30–40 undifferentiated larvae were fed with a diet containing varying amounts of E2 for 28 days, and fish were sampled at 90 dph. Previous studies revealed that ovary formation in A. altiparanae occurred at 58 dph, whereas the first sign of testis formation was found at 73 dph. In relation to the control, E2 exposure increased the proportion of phenotypic females in 120% and 148.4% for 4 and 6 mg E2/Kg, respectively. However, histological analysis revealed that treatments did not affect gonadal sex ratio between males and females, but induced intersex (testis-ova) in the group treated with 6 mg E2/Kg food. Treatment with E2 also altered gonadal transcript levels of a selected number of genes implicated in sexual differentiation. Males overexpressed dmrt1, sox9 and amh following E2 treatment as compared to control. Females showed increased mRNA levels of dmrt1 and sox9, which might be related to the down-regulation of cyp19a1a after E2 exposure. In summary, E2 exposure during early gonadal development affected male secondary characteristics without changing the gonadal sex ratio, and altered expression of genes implicated in sexual differentiation.

与其他脊椎动物相比，硬骨鱼类的性腺性别分化表现出更大的可塑性，因为它可能受到多种因素的影响，例如外源性类固醇。外源性雌激素，例如17β-雌二醇（E2），在早期胚胎发育过程中给药可诱导女性化。但是，尚不完全了解E2诱导女性化的机制，尤其是在新热带物种中。因此，本研究的目的是评估E2给药对表型性别特征，性腺的组织学评估以及在Astyanax altiparanae中所选基因的表达的影响。在性腺分化之前接触饮食E2。孵化后第4天（dph），对30至40只未分化幼虫的组饲喂含不同量E2的饮食28天，并以90 dph采样鱼。先前的研究表明，A。altiparanae的卵巢形成发生在58 dph，而形成睾丸的第一个迹象是在73 dph。与对照组相比，E2暴露使4和6 mg E2 / Kg的表型雌性比例分别增加120％和148.4％。但是，组织学分析表明，在用6 mg E2 / Kg食物治疗的组中，治疗并不影响男女之间的性腺性别比，而是诱导了性交（睾丸-卵）。用E2处理还改变了与性别分化有关的选定基因的性腺转录本水平。与对照相比，男性在E2处理后过表达dmrt1，sox9和amh。女性显示dmrt1和sox9的mRNA水平升高，这可能与E2暴露后cyp19a1a的下调有关。总之，早期性腺发育过程中的E2暴露影响了男性的次要特征，而没有改变性腺性别比，并且改变了与性别分化有关的基因的表达。