Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground.

中文翻译：

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日本东北东北地区太平洋沿岸太平洋蓝鳍金枪鱼东方金枪鱼幼虫的发生：发现第三产卵场的可能性

最近，根据组织学研究表明，太平洋蓝鳍金枪鱼（PBF）产自日本东北部太平洋沿岸的黑潮-御潮尾过渡带，此外还包括先前确定的南塞群岛周围西北太平洋的两个产卵区和日本海。黑潮-矢潮过渡期尚未进行过PBF幼虫的分布调查，因此，我们于2018年8月上旬在该地区的20个站进行了PBF幼虫调查，以获取PBF产卵的证据。在六个台站收集了十二只PBF幼虫（体长3.9-7.2毫米），这些台站的海面温度范围为27.2至28.2°C。耳石的显微结构分析表明，这些幼虫的年龄在孵化后的4到11天不等，并且在7月下旬孵化。收集到的幼虫的生长与其他两个产卵场的生长相当。因此，在黑潮—大潮过渡期孵化后11天，PBF会产卵，孵化，并且至少可以存活到屈曲后阶段。如果这些事实在第三个产卵场中幸存下来，可能会对PBF的募集过程产生重大影响。