生物時計と潮汐によるサンゴ礁棲ベラ類の産卵時刻あわせ

珊瑚礁中的许多濑鱼每天都会产卵，在白天涨潮时达到顶峰。在这项研究中，我们研究了印度太平洋珊瑚礁中常见的三斑濑鱼（Halichoeres trimaculatus）与潮汐相关的卵巢发育。在不同潮位的早晨采集，性腺指数（GSI）和卵巢组织学发生变化；随着GSI向高潮方向增加，一批最先进的卵母细胞从卵黄细胞发育到成熟阶段。涨潮前后大多数卵巢存在排卵卵和排卵后卵泡（POF），而退潮前后只有POF存在，表明产卵发生在涨潮期间或之后。我们注意到，与潮汐相关的产卵在上午显著，而在下午涨潮时收集的大多数子房表现出产卵后的特征。结果表明，某些物种在产卵时间方面具有可塑性，并利用有效的环境线索来繁殖成功。用前体类固醇孵育卵巢块时，睾酮在涨潮和退潮时大量转化为17β-雌二醇，而17α-羟孕酮在退潮和涨潮时大量转化为17α，20β-二羟基-4-孕-3- 1和17α，20β，21-三羟基-4-孕-3- 1。卵巢片与人绒毛膜促性腺激素孵育后，类固醇激素的波动与潮汐相似。这些类固醇激素的产生与卵巢中卵母细胞的发育有关，并可能受促性腺激素的调节。这些结果表明，日周期是卵母细胞发育的基础，潮汐周期叠加在此过程中。

Many wrasses in coral reefs exhibit daily spawning that peaks around daytime high tide. In this study, we examined tidal-related ovarian development in the threespot wrasse Halichoeres trimaculatus, which is a common species in coral reefs of the Indo-Pacific Ocean. When the fish were collected in the morning at different tidal phases, the gonadosomatic index (GSI) and ovarian histology changed; concomitant with increases in GSI towards high tide, a clutch of the most advanced oocytes developed from vitellogenic to maturation stages. Ovulated eggs and post-ovulated follicles (POF) existed in most ovaries around high tide, but only POF remained around ebb tide, suggesting that spawning occurred during or after high tide. We noticed that tidal-related spawning was remarkable in the morning and that most ovaries collected at afternoon high tide exhibited post-spawning features. It was suggested that certain labrid species possess plasticity with regard to their spawning time and utilize potent environmental cues for their reproductive success. When the ovarian pieces were incubated with precursor steroids, high conversion of testosterone to 17β-estradiol occurred during high and ebb tides, while that of 17α-hydroxyprogesterone to 17α,20β-dihydroxy-4-pregnen-3-one and 17α,20β,21-trihydroxy-4-pregnen-3-one was observed during low and flood tides. Incubation of the ovarian pieces with human chorionic gonadotropin resulted in similar fluctuations of the steroid hormones with tide. Production of these steroid hormones correlated with oocyte development in the ovaries and was probably regulated by gonadotropin. These results demonstrate that the daily cycle is fundamental for oocyte development, and the tidal cycle is superimposed on this process.