| Summary: | Global warming has led to rising water temperatures, posing a significant threat to fish survival. Understanding the mechanisms by which fish respond to and adapt to temperature variations is thus of considerable importance. This study employed high-throughput 16S rRNA gene sequencing and bioinformatics to investigate changes in the intestinal microbiota of the kaluga sturgeon (<i>Huso dauricus</i>) under four temperature conditions (19 °C, 25 °C, 28 °C, and 31 °C) and its relationship with adaptation to high-temperature stress. The results indicated that temperature variations caused significant changes in the intestinal microbiota. Over time, differences in the microbiota structure became more pronounced under different temperature conditions, and within-group variability gradually decreased. At higher temperatures, the relative abundance of <i>Sphingomonas</i> significantly decreased, while that of <i>Clostridium sensu stricto 1</i>, <i>Cetobacterium</i>, and <i>Plesiomonas</i> exhibited a significant increase in relative abundance. Upon the cessation of rapid mortality under various high-temperature conditions, the intestinal microbiota structure and composition became highly similar, with <i>Clostridium sensu stricto 1</i> dominating both in terms of composition and relative abundance, suggesting a central role in adaptation to high-temperature stress. This study preliminarily confirms that the high-temperature adaptability of <i>Huso dauricus</i> is closely related to the structure and composition of its intestinal microbiota, with bacteria such as <i>Clostridium sensu stricto 1</i> playing an important role. These findings provide new scientific insights into enhancing fish adaptability to high-temperature stress.
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