Shimizu Akio
National Research Institute of Fisheries Science, Fisheries Research Agency, Fukuura 2-12-4, Kanazawa, Yokohama 236-8648, Japan.
Gen Comp Endocrinol. 2003 May;131(3):310-24. doi: 10.1016/s0016-6480(03)00026-1.
Mummichog, a spring and summer spawning teleost, were exposed to various photoperiod and temperature conditions to investigate the environmental regulation of the annual reproductive cycle. In early spring, latter phases of gonadal development (vitellogenesis in females and active spermatogenesis in males) were effectively accelerated by warm temperature (16 degrees C) regardless of the photoperiod (11L or 16L), although internal factor(s) may be concerned with triggering the initiation of the development. In late summer, intense gonadal regression which leads to the termination of the spawning period was accelerated by a short day length (</=13L) in both yearlings and underyearlings. In underyearlings, however high water temperature and internal factor(s) may also be concerned. In early autumn, early phases of gonadal development (growth of cortical alveolus stage oocytes in females and basal spermatogenesis in males) were induced by moderate or lower temperatures (</=22 degrees C) even under a short day length (11L). From the middle of autumn to early winter, this fish is probably in the "refractory period," and did not progress to the latter phases even under adequate temperature and long day length conditions (22 degrees C-16L). Mummichog showed a probable circa-annual rhythm of gonadal activity under constant temperature and photoperiod conditions (22 degrees C-16L): this rhythm may be the basis of the trigger of the gonadal development prior to the spawning period, the termination of the spawning period in underyearlings, and the occurrence of the "refractory period" during autumn. Plasma concentrations of estradiol-17beta in females and testosterone in males correlated well with the gonadal development during early spring and the regression during late summer. However, there was no correlation between plasma steroid levels and the degree of progress during the early phases of gonadal development in autumn, suggesting other factor such as direct action of GtH(s) or mediating substance other than sex steroids for these phases.
将鲦鱼（一种在春季和夏季产卵的硬骨鱼）置于不同的光照周期和温度条件下，以研究年度繁殖周期的环境调节机制。早春时节，无论光照周期如何（11小时光照或16小时光照），温暖的温度（16摄氏度）都能有效加速性腺发育的后期阶段（雌性的卵黄生成和雄性的活跃精子发生），尽管可能有内部因素参与触发发育的起始。夏末时，一岁龄和幼龄鱼中，短日照（≤13小时光照）会加速导致产卵期结束的强烈性腺退化。然而，在幼龄鱼中，高水温及内部因素可能也起到了作用。初秋时，即使在短日照（11小时光照）下，中等或更低的温度（≤22摄氏度）也能诱导性腺发育的早期阶段（雌性皮质泡期卵母细胞的生长和雄性的基础精子发生）。从秋季中期到初冬，这种鱼可能处于“不应期”，即使在适宜的温度和长日照条件下（22摄氏度 - 16小时光照）也不会进入后期阶段。鲦鱼在恒温恒光条件下（22摄氏度 - 16小时光照）表现出可能的近似年度性腺活动节律：这种节律可能是产卵期前性腺发育触发、幼龄鱼产卵期结束以及秋季“不应期”出现的基础。雌性血浆中雌二醇 - 17β和雄性血浆中睾酮的浓度与早春性腺发育及夏末性腺退化密切相关。然而，秋季性腺发育早期阶段血浆类固醇水平与发育进程程度之间没有相关性，这表明在这些阶段存在其他因素，如促性腺激素的直接作用或除性类固醇之外的介导物质。
