Limited Hypoxia Tolerance in the Critically Endangered Chinese Sturgeon ( Acipenser sinensis ): Insights from Histological and Transcriptional Analysis

The Chinese sturgeon (Acipenser sinensis), as one of the oldest bony fish species, has extremely high ecological and economic significance but is endangered. In this work, we assessed hypoxia sensitivity via ASR (aquatic surface respiration), LOE (loss of equilibrium), and LC50 (median lethal concentration), revealing that the Chinese sturgeon is hypoxia-sensitive compared to other teleosts. We also systematically investigated the morphological changes of the gill tissues and the transcriptomic responses of the gills and the livers of Chinese sturgeon under normal oxygen conditions and after hypoxic exposure for 2, 6, and 24 h. The interlamellar cell mass (ILCM) width and lamellar width were significantly decreased in samples treated up to hypoxia for 24 h. Transcriptomic profiling identified 522, 494, and 437 differentially expressed genes (DEGs) in gills and 488, 765, and 597 DEGs in liver at hypoxia for 2, 6, and 24 h, respectively. During early hypoxic exposure (2–6 h), we observed upregulation of proliferation-related transcription genes (e.g., NR4A1, NR4A2, FOS, and MMP9) followed by upregulation of glycolysis-related genes (e.g., LDH, PFKAL, G6PI, and ALDOC), particularly at 6 h. Concurrently, hypoxia suppressed gill functions involving immunity, neurotransmitters and ion transport, and synthesis of microtubule-associated proteins and lipogenesis in the liver.