Studies on Perception of Moonlight in the Golden Rabbitfish, a Lunar-synchronized Spawner

众所周知，兔子鱼在特定物种的月相前后同步产卵。据认为，他们认为，并利用线索，从月球，以同步性腺发育和产卵与月球周期。利用在繁殖季节的上弦月前后同步产卵的金兔鱼Siganus guttatus，我们测量了褪黑激素水平的波动，并研究了鱼对月光强度的反应。黄姑鱼血液中褪黑激素浓度的日波动表现为白天低，夜间高，表明褪黑激素在光周期的感知和利用中存在波动。新月时血浆褪黑素浓度高于满月时。当鱼暴露在月光下的午夜两个月相，褪黑激素浓度下降到对照水平。这些结果表明，鱼可能感知月光强度和血浆褪黑激素波动根据“亮度”在夜间的一个点。在第一次产卵期（产卵前一个月开始试验），在昼夜恒定的黑暗和光照下饲养的鱼不产卵。在第二次产卵期（实验在产卵前2周开始），在自然和恒定黑暗的夜晚条件下饲养的鱼产卵，而不是恒定明亮的夜晚。夜间条件可能与金兔鱼的性腺发育和产卵同步有关

Rabbitfishes are known to spawn synchronously around the species-specific lunar phase. It is considered that they perceive and utilize cues from the moon in order to be synchronized gonadal development and spawning with the lunar-cycle. Using the golden rabbitfish, Siganus guttatus, which spawns synchronously around the first quarter moon during the reproductive season, we measured the fluctuation of melatonin levels and examined the response of the fish to moonlight intensity. Daily fluctuations of melatonin concentration in the blood of golden rabbitfish showed low levels during daytime and high levels during night-time, suggesting that melatonin fluctuation in the perception and utilization of photoperiod. Plasma melatonin concentration at the new moon was higher than that at the full moon. When the fish were exposed to moonlight at midnight of the both moon phases, the melatonin concentrations decreased to the control levels. These results show that the fish possibly perceive moonlight intensity and plasma melatonin fluctuates according to 'lightness' at a point of night. At the first spawning period(experiment was started one month before the spawning), the fish reared under the constant darkness and lightness of nigh did not spawn. At the second spawning period(experiment was started 2 weeks before the spawning), the fish reared under the conditions of natural and constant darkness of night spawned but not that of constant lightness of night. It is possible that night conditions are related to synchronous gonadal development and spawning in the golden rabbitfish