Fish typically adapt to their environment through evolutionary traits, and this adaptive strategy plays a critical role in promoting species diversity. Onychostoma macrolepis is a rare and endangered wild species that exhibits a life history of overwintering in caves and breeding in mountain streams. We analyzed the morphological characteristics, histological structure, and expression of circadian clock genes in O. macrolepis to elucidate its adaptive strategies to environmental changes in this study. The results showed that the relative values of O. macrolepis eye diameter, body height, and caudal peduncle height enlarged significantly during the breeding period. The outer layer of the heart was dense; the ventricular myocardial wall was thickened; the fat was accumulated in the liver cells; the red and white pulp structures of the spleen, renal tubules, and glomeruli were increased; and the goblet cells of the intestine were decreased in the breeding period. In addition, the spermatogenic cyst contained mature sperm, and the ovaries were filled with eggs at various stages of development. Throughout the overwintering period, the melano-macrophage center is located between the spleen and kidney, and the melano-macrophage center in the cytoplasm has the ability to synthesize melanin, and is arranged in clusters to form cell clusters or white pulp scattered in it. Circadian clock genes were identified in all organs, exhibiting significant differences between the before/after overwintering period and the breeding period. These findings indicate that the environment plays an important role in shaping the behavior of O. macrolepis, helping the animals to build self-defense mechanisms during cyclical habitat changes. Studying the morphological, histological structure and circadian clock gene expression of O. macrolepis during the overwintering and breeding periods is beneficial for understanding its unique hibernation behavior in caves. Additionally, it provides an excellent biological sample for investigating the environmental adaptability of atypical cavefish species.

鱼类通常通过进化特征来适应环境，这种适应策略在促进物种多样性方面发挥着关键作用。大鳞甲鱼是一种珍稀濒危野生物种，具有在洞穴中越冬、在山涧中繁殖的生活史。在本研究中，我们分析了大鳞鱼的形态特征、组织结构和生物钟基因的表达，以阐明其对环境变化的适应策略。结果表明，在繁殖期间，大鳞卵眼径、体高、尾柄高度的相对值显着增大。心脏的外层致密；心室心肌壁增厚；脂肪堆积在肝细胞中；脾、肾小管、肾小球的红、白髓结构增多；繁殖期肠道杯状细胞减少。此外，生精囊肿中含有成熟的精子，卵巢中充满了处于不同发育阶段的卵子。整个越冬期间，黑色素巨噬细胞中心位于脾、肾之间，细胞质中的黑色素巨噬细胞中心具有合成黑色素的能力，并呈簇状排列，形成细胞簇或散在其中的白髓。所有器官中均发现了昼夜节律基因，越冬前后和繁殖期之间表现出显着差异。这些发现表明，环境在塑造大鳞鳞鱼的行为方面发挥着重要作用，帮助动物在周期性栖息地变化期间建立自我防御机制。研究大鳞鳞鱼越冬和繁殖期的形态、组织结构和生物钟基因表达，有助于了解其独特的洞穴冬眠行为。此外，它还为研究非典型洞穴鱼类的环境适应性提供了极好的生物样本。