We examined the annual reproductive cycle of both female and male hatchery-produced Pacific bluefin tuna (PBT, Thunnus orientalis) broodstock at 3 years of age, including the associated changes in plasma levels of sex steroid hormones and the gene expression of key endocrine factors. The females progressed to vitellogenesis in April, and approximately 50% of the females were observed in late vitellogenesis between June and July at water temperatures between 24.1 °C and 29.0 °C. Approximately 90% of the males were in spermiation for at least 7 months between April and October, which included the period when vitellogenic females were present. Furthermore, the gonadosomatic index of both females and males peaked between June and July. These results indicate that the reproductive season of hatchery-produced PBT peaks between June and July, which is in agreement with the reproductive season reported for PBT broodstock originating from wild-caught juveniles. Furthermore, the percentage of hatchery-reared females that reached late vitellogenesis in the present study was higher than that in wild-caught captive-reared females reported in previous literature. Analysis of plasma sex steroid levels and gene expression profiles suggested that oocyte and ovarian development were associated with 17β-estradiol (E2) control, whereas spermatogonial differentiation towards meiosis seemed to be mediated by 11-ketotestosterone (11-KT). Furthermore, the production of E2 and 11-KT is likely regulated by luteinizing hormone and follicle-stimulating hormone, respectively, via their related receptors. The findings of this study are expected to contribute to improvements of technologies for obtaining fertilized eggs from hatchery-produced PBT broodstock.

我们检查了雌性和雄性孵化场生产的太平洋蓝鳍金枪鱼（PBT、Thunnus orientalis) 3 岁时亲鱼，包括性类固醇激素血浆水平的相关变化和关键内分泌因子的基因表达。雌性在 4 月份进展到卵黄生成，在 6 月和 7 月之间在 24.1°C 和 29.0°C 之间的水温下观察到大约 50% 的雌性在卵黄生成后期。大约 90% 的雄性在 4 月到 10 月之间至少有 7 个月的精子形成，其中包括生卵雌性雌性的时期。此外，女性和男性的性腺体指数在 6 月和 7 月之间达到顶峰。这些结果表明孵化场生产的 PBT 的繁殖季节在 6 月和 7 月之间达到高峰，这与报告的来自野生捕获的幼鱼的 PBT 亲鱼的繁殖季节一致。此外，本研究中孵化场饲养的雌性达到卵黄形成后期的百分比高于先前文献报道的野生捕获的圈养饲养的雌性。血浆性类固醇水平和基因表达谱的分析表明，卵母细胞和卵巢发育与 17β-雌二醇 (E2) 控制相关，而精原细胞向减数分裂的分化似乎是由 11-酮睾酮 (11-KT) 介导的。此外，E2 和 11-KT 的产生可能分别由促黄体激素和促卵泡激素通过其相关受体调节。预计本研究的结果将有助于改进从孵化场生产的 PBT 亲鱼中获取受精卵的技术。