Kondo Yuki, Awata Satoshi
Laboratory of Animal Sociology, Department of Biology, Graduate School of Science, Osaka Metropolitan University, Osaka, 558-8585, Japan.
Sci Rep. 2025 May 16;15(1):17057. doi: 10.1038/s41598-025-01037-8.
Reproductive timing is a critical ecological trait that directly influences fitness. Medaka (Oryzias latipes), a small freshwater fish, is widely used as a model organism in various scientific fields. However, ecological studies conducted under (semi-) natural conditions remain limited. Although, spawning has been reported to occur within 1 h before and after sunrise, direct observations remain scarce. We investigated the timing of spawning initiation and associated courtship in medaka through 24-h observations using infrared cameras under semi-natural conditions. During the experiments, sunrise occurred at approximately 4:45. Observations of the 31 pairs revealed that spawning occurred between 1:05-9:48, with a peak at 2:00-4:00. Unlike previous reports but like the most recent fieldwork, only 26% of the total spawning events (8/31) were observed within 1 h before and after sunrise. Male courtship behaviours, including following females and quick circle displays, increased from midnight, peaking between 2:00-5:00. This study provides new insights into the natural reproductive timing of medaka, suggesting a possible adaptation to nocturnal spawning, likely as a strategy to reduce predation on both parents and eggs. It also underscores the importance of investigating the ecology of model organisms under (semi-)natural conditions to gain a more comprehensive understanding of biological phenomena observed in laboratory settings.
繁殖时机是一种直接影响适合度的关键生态特征。青鳉（Oryzias latipes）是一种小型淡水鱼，在各个科学领域被广泛用作模式生物。然而，在（半）自然条件下进行的生态研究仍然有限。尽管有报道称产卵发生在日出前后1小时内，但直接观察仍然很少。我们在半自然条件下使用红外摄像机通过24小时观察，研究了青鳉产卵开始的时间和相关求偶行为。实验期间，日出时间约为4:45。对31对青鳉的观察发现，产卵发生在1:05 - 9:48之间，高峰期在2:00 - 4:00。与之前的报道不同，但与最近的实地研究相似，在日出前后1小时内仅观察到26%（8/31）的总产卵事件。雄性求偶行为，包括跟随雌性和快速绕圈展示，从午夜开始增加，在2:00 - 5:00之间达到峰值。这项研究为青鳉的自然繁殖时机提供了新的见解，表明可能适应夜间产卵，这可能是一种减少对亲代和卵的捕食的策略。它还强调了在（半）自然条件下研究模式生物生态学对于更全面理解在实验室环境中观察到的生物现象的重要性。
