Impact of Hypoxia on Intestinal Health and Gut Microbiota in Anadara granosa

Dissolved oxygen (DO) is a crucial determinant of aquatic organism health. This study demonstrates that hypoxia (at MH, 2.0 mg/L; SH, 0.5 mg/L) disrupts intestinal homeostasis in the blood clam, Anadara granosa. Exposure to hypoxia induced severe histopathological damage, including villus loss, inflammatory cell infiltration, and epithelial cell vacuolization. Immune-related gene expression analysis revealed coordinated regulation, with TLR4 and NF-κB significantly up-regulated by 4.5-fold and 5-fold, respectively, in the SH14 group, while HSP70 showed a remarkable 13-fold increase in the MH14 group. In contrast, TAK1 and TRAF6 exhibited substantial downregulation. High-throughput sequencing of the 16S rRNA gene revealed a significant reduction in gut microbiota diversity under hypoxic conditions, as evidenced by notable decreases of approximately 30% in the Chao1 index and 35% in the Shannon index in the SH group compared to the normoxic control (N group). Functional pathway analysis indicated alterations in pathways associated with xenobiotic biodegradation, lipid metabolism, and energy metabolism. These findings highlight a strong association between hypoxia and adverse intestinal health outcomes in A. granosa, underscoring the critical importance of maintaining adequate dissolved oxygen levels to support bivalve health. Future research should aim to develop strategies to mitigate hypoxia-induced stress and further elucidate the molecular mechanisms underlying hypoxia adaptation in bivalves.