Gerkema M P, Videler J J, de Wiljes J, van Lavieren H, Gerritsen H, Karel M
Zoological Laboratory, University of Groningen, Haren, Netherlands.
Chronobiol Int. 2000 Sep;17(5):613-22. doi: 10.1081/cbi-100101068.
Yellow wrasses (Halichoeres chrysus) show clear daily activity patterns. The fish hide in the substrate at (subjective) night, during the distinct rest phase. Initial entrainment in a 12h:12h light-dark (12:12 LD) cycle (mean period 24.02h, SD 0.27h, n = 16) was followed by a free run (mean period 24.42h, SD 1.33h) after transition into constant dim light conditions. Light pulses of a comparable intensity as used in the light part of the LD cycles did not result in significant phase shifts of the free-running rhythm in constant darkness. Application of much brighter 3h light pulses resulted in a phase-response curve (PRC) for a fish species, with pronounced phase advances during late subjective night. The PRCs differed from those mainly obtained in other vertebrate taxa by the absence of significant phase delays in the early subjective night. At that circadian phase, significant tonic effects of the light pulses caused a shortening of the circadian period length. Entrainment to skeleton photoperiods of 1:11 LD was observed in five of six wrasses exposed, also after a 3h phase advance of this LD cycle. Subsequently, a 1:11.25 LD cycle resulted in entrainment in four of the six fish. It is suggested that the expression of the circadian system in fish can be interpreted as a functional response to a weak natural zeitgeber, as present in the marine environment. This response allows photic entrainment as described here in the yellow wrasse.
黄拟隆头鱼（Halichoeres chrysus）表现出明显的每日活动模式。在（主观）夜间，即在明显的休息阶段，这种鱼会藏在水底。最初，16条鱼在12小时光照：12小时黑暗（12:12 LD）周期（平均周期24.02小时，标准差0.27小时）中进行了初始同步化，之后在转入持续昏暗光照条件后进入自由运行阶段（平均周期24.42小时，标准差1.33小时）。与LD周期光照部分强度相当的光脉冲，在持续黑暗条件下并未导致自由运行节律发生显著的相位偏移。施加更亮的3小时光脉冲，得到了一种鱼类的相位响应曲线（PRC），在主观夜间后期出现了明显的相位提前。该PRC与主要在其他脊椎动物类群中获得的PRC不同，在于主观夜间早期没有显著的相位延迟。在那个昼夜节律阶段，光脉冲的显著强直效应导致昼夜周期长度缩短。在暴露的六条拟隆头鱼中，有五条在1:11 LD的骨骼光周期下实现了同步化，即使该LD周期提前了3小时。随后，1:11.25 LD周期使六条鱼中的四条实现了同步化。有人认为，鱼类昼夜节律系统的表达可以被解释为对海洋环境中存在的微弱自然授时因子的一种功能反应。这种反应使得黄拟隆头鱼能够像这里所描述的那样进行光同步化。
