In fish, as in higher animals, the normal ontogenesis of the gonads is the basis for successful reproduction. Gonadal differentiation and development depend on the genetic cascade that programmes the events. Eventually, gonads become the sites for the maturation of gametes, which are originally derived from the primordial germ cells (PGCs) and form the cellular basis of reproduction. In fish hormones of the hypothalamic–pituitary–gonadal (HPG) axis regulate reproduction and fertility by promoting or inhibiting the production of gonadal sex steroids and their function. Gonadal sex steroids not only guide proper gonadal development and function but also play a key role in the activation and regulation of the HPG axis through two feedback control systems. In this review, we discuss the general outline and expression pattern of the major genes involved in testicular development and gonadal steroidogenesis in fish. The review attempts, for the first time, to collect and discuss recent information regarding the regulation of sex differentiation and steroidogenic genes during the stages of testicular development and in response to different external factors. Furthermore, clear insights into the important genes and their regulation involved in the HPG axis and spermatogenesis are presented briefly. This review can serve as a guide for fish breeders on the substances that have a positive impact on reproduction in males.

中文翻译：

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鱼的睾丸发育和精子发生：不同外源因素对分子方面和基因表达调控的洞察

在鱼类中，与高等动物一样，性腺的正常个体发育是成功繁殖的基础。性腺分化和发育取决于对事件进行编程的遗传级联。最终，性腺成为配子成熟的场所，配子最初来自原始生殖细胞 (PGC)，并形成繁殖的细胞基础。在鱼类中，下丘脑-垂体-性腺 (HPG) 轴的激素通过促进或抑制性腺性类固醇的产生及其功能来调节生殖和生育能力。性腺性类固醇不仅指导性腺正常发育和功能，而且还通过两个反馈控制系统在 HPG 轴的激活和调节中发挥关键作用。在这次审查中，我们讨论了与鱼类睾丸发育和性腺类固醇生成有关的主要基因的总体轮廓和表达模式。该综述首次尝试收集和讨论有关睾丸发育阶段和对不同外部因素的反应的性别分化和类固醇生成基因调控的最新信息。此外，还简要介绍了对涉及 HPG 轴和精子发生的重要基因及其调控的清晰见解。该综述可作为鱼类育种者关于对雄性繁殖产生积极影响的物质的指南。收集和讨论有关睾丸发育阶段和对不同外部因素的反应的性别分化和类固醇生成基因调控的最新信息。此外，还简要介绍了对涉及 HPG 轴和精子发生的重要基因及其调控的清晰见解。该综述可作为鱼类育种者关于对雄性繁殖产生积极影响的物质的指南。收集和讨论有关睾丸发育阶段和对不同外部因素的反应的性别分化和类固醇生成基因调控的最新信息。此外，还简要介绍了对涉及 HPG 轴和精子发生的重要基因及其调控的清晰见解。该综述可作为鱼类育种者关于对雄性繁殖产生积极影响的物质的指南。