Identifying environmental effects on the reproduction cycle and sex hormones is essential for ensuring the sustainable productivity of Pacific bluefin tuna (PBT, Thunnus orientalis) aquaculture. In the present study, 70 PBTs, commercially farmed in sea cages near Yokjido Island, South Korea, were investigated from April 2020 to March 2021. Environmental data, including water temperature and photoperiod duration, were collected. The gonadosomatic index (GSI) was calculated, and male and female maturity stages were classified monthly in proportions based on histological analysis of the gonads. Male and female gonadal developmental stages were classified into four major stages. Mature male and female PBTs were observed from May to August and June to August, respectively. Monthly changes in sex steroid hormone levels in PBT plasma were evaluated. The GSI and sex steroid hormones of males and females increased in May, peaked in June, and decreased thereafter. Our results confirmed the reproductive potential of farmed PBT and verified that reproductive maturity is reached in July. This study, to the best of our knowledge, is the first to investigate the reproductive biology of PBT in South Korea, and our results constitute a reference for future research on PBT aquaculture.

中文翻译：

---

韩国网箱养殖太平洋蓝鳍金枪鱼（Thunnus orientalis）的繁殖潜力

确定环境对繁殖周期和性激素的影响对于确保太平洋蓝鳍金枪鱼（PBT，Thunnus orientalis）水产养殖的可持续生产力至关重要。在本研究中，2020年4月至2021年3月对韩国Yokjido岛附近的海水网箱商业养殖的70种PBT进行了调查。收集了包括水温和光周期持续时间在内的环境数据。计算性腺体指数（GSI），并根据性腺的组织学分析每月按比例对雄性和雌性成熟阶段进行分类。男性和女性性腺发育阶段分为四个主要阶段。成熟雄性和雌性PBT分别在5月至8月和6月至8月观察。评估 PBT 血浆中性类固醇激素水平的每月变化。男性和女性的GSI和性类固醇激素在5月份上升，6月份达到峰值，此后下降。我们的结果证实了养殖 PBT 的繁殖潜力，并证实其在 7 月达到繁殖成熟。据我们所知，这项研究是韩国首次调查PBT的生殖生物学，我们的结果为未来PBT水产养殖的研究提供了参考。