Okuzawa K, Furukawa K, Aida K, Hanyu I
Department of Fisheries, Faculty of Agriculture, University of Tokyo, Japan.
Gen Comp Endocrinol. 1989 Jul;75(1):139-47. doi: 10.1016/0016-6480(89)90019-1.
The honmoroko (Gnathopogon caerulescens), a small, spring-summer-breeding cyprinid fish, was exposed to various temperature and photoperiod regimes during different phases of its annual reproductive cycle. In autumn, a clear photoperiodism was seen, especially at warm temperatures (18-24 degrees). The gonadosomatic index, plasma gonadotropin (GtH), and gonadal steroids were higher in fish held at long photoperiod (15L/9D) than in those held at short photoperiod (12L/12D); the differences were greater as the temperature increased. In early spring, gonadal recrudescence progressed at temperatures above 7 degrees, regardless of photoperiod. Photoperiod did not affect plasma GtH and gonadal steroid levels at this time of the year. During its spawning season, a long photoperiod (15L/9D) was again required to maintain gonadal activity and high plasma GtH and gonadal steroid levels, especially at high temperature (25 degrees). In early summer, high temperatures (25 and 30 degrees) suppressed gonadal activity; however, gonadal steroid levels were not depressed, and plasma GtH levels actually increased. The data suggest that under natural conditions, high water temperatures in summer may act directly at the gonadal level, and is probably the factor which terminates the breeding season for this species. The results of these four experiments indicate that the honmoroko exhibits a photoperiodic response during the autumn month and its spawning season, and is dependent on the water temperature. The effects of photoperiod on gonadal maturation appear to be GtH mediated, whereas the suppressive effects of high temperature are not.
日本鲫（Gnathopogon caerulescens）是一种小型的鲤科鱼类，在春夏季节繁殖。在其年度繁殖周期的不同阶段，该鱼被置于不同的温度和光照周期条件下。秋季时，出现了明显的光周期现象，尤其是在温暖的温度（18 - 24摄氏度）下。与处于短光照周期（12小时光照/12小时黑暗，12L/12D）的鱼相比，处于长光照周期（15小时光照/9小时黑暗，15L/9D）的鱼的性腺指数、血浆促性腺激素（GtH）和性腺类固醇水平更高；随着温度升高，差异更大。早春时节，无论光照周期如何，性腺在7摄氏度以上的温度下开始复苏。在一年中的这个时候，光照周期不影响血浆GtH和性腺类固醇水平。在其产卵季节，同样需要长光照周期（15L/9D）来维持性腺活动以及高血浆GtH和性腺类固醇水平，尤其是在高温（25摄氏度）下。初夏时，高温（25和30摄氏度）会抑制性腺活动；然而，性腺类固醇水平并未降低，血浆GtH水平实际上还增加了。数据表明，在自然条件下，夏季的高水温可能直接作用于性腺水平，这可能是该物种繁殖季节结束的因素。这四项实验的结果表明，日本鲫在秋季月份及其产卵季节表现出光周期反应，并且依赖于水温。光周期对性腺成熟的影响似乎是由GtH介导的，而高温的抑制作用则并非如此。
