Study on the mechanism of lunar-related spawning in honeycomb grouper

分布于太平洋亚热带和热带地区的蜂巢石斑鱼Aainephelus merra被称为与月球有关的产卵。然而，这种物种的性腺发育和产卵的细节还不是很清楚。在本研究中，我们调查了产卵季节在冲绳Sesoko岛和Iriomote岛周围礁区采集的雌性性腺发育、激素变化和促性腺激素基因的表达。此外，我们还利用生物遥测的方法研究了产卵迁移到适宜产卵的环境中，两个地区采集的鱼的卵巢都被第三次卵黄期的卵子占据，此时性腺指数增加，在满月前后达到最大水平。Ireornete岛的成鱼体型小于Sesoko岛。此外，在产卵季节之后，Treomote的鱼立即开始了雌性到雄性的转变。另一方面，从Sesoko岛采集的鱼在产卵季节过后几个月就开始发生性别变化。这两个区域的不同特征可能取决于密度、礁石生态位、深度、水流和水温的不同。雌二醇水平在产卵前显示很高。黄体生成素β亚基基因在雌性石斑鱼生殖期表达，提示黄体生成素在性腺发育和类固醇合成中起重要作用。在这两个地区，满月后鱼类都从栖息地迁徙到适宜产卵的环境中。似乎环境中有进行产卵行为所需的水深。

The honeycomb grouper ainephelus merra, which is distributed in the sub-tropical and tropical area in Pacific Ocean, is known as a lunar-related spawning. However, details of gonadal development and spawning in this species are not well understood. In this study, we investigated the gonadal development, hormonal changes, and expression of gonadotropin gene in female collected from the reef area around Sesoko Island and Iriomote Island in Okinawa during spawning season. In addition, we investigated the spawning migration to suitable environment for spawning using biotelemetry method.Ovaries of fish collected in both areas were occupied with oocytes of the tertiary yolk stage, when gonadosomatic index increased and reached the maximum level around full moon. However, mature size of fish in Ireornete Island was smaller than that in Sesoko Island. Moreover, fish of Treomote started female-to-male sex change immediately after the spawning season. On the other hand, sex change in fish collected from Sesoko Island stared in a few months after the spawning season. The different characteristics in both areas may depend on the difference in density, niche in the reefs, depth, water current, and water temperature. Estradiol levels indicated high just prior to spawning. Luteinizing hormone beta subunit gene expressed during reproductive period in female grouper, suggesting LH has important roles on gonadal development and steroid synthesis. In both areas, the fish migrated to suitable environment for spawning from habitat place just after full moon. It appears that the environment has water depth necessary to do the spawning behavior.