Disruption mechanism of total dissolved gas supersaturation to fish development, survival and locomotion

The expansion of hydropower infrastructure has increased the prevalence of total dissolved gas (TDG) supersaturation, posing significant threats to aquatic organisms. However, the impacts of TDG on immune function and energy metabolism across fish life stages remain insufficiently characterized. This study evaluated TDG effects on Danio rerio and Schizothorax davidi by integrating development, hatching, survival, locomotion and transcriptomic analyses across embryos and juveniles. Exposure to 130 % TDG significantly reduced embryonic survival and hatching rates in both species, with larvae displaying gas bubble trauma (GBT), growth inhibition, and elevated heart rates. Transcriptomic data revealed species-specific responses: Danio rerio larvae exhibited activation of Toll-like receptor-mediated innate immunity and suppressed ATP synthase gene expression, indicating energy metabolism impairment, whereas Schizothorax davidi showed complement system dysregulation and compromised protein homeostasis. Acute lethality tests indicated greater TDG sensitivity in Schizothorax davidi than Danio rerio. Both species experienced impaired swimming capacity and reduced metabolic performance, with distinct molecular adaptation strategies observed in gill tissues. Danio rerio prioritized energy allocation to antigen processing, while Schizothorax davidi relied on low-energy innate pathways. These findings highlight species- and stage-specific mechanistic disruptions induced by TDG supersaturation. The results provide crucial insights for ecological risk assessment and inform conservation strategies for aquatic species in regulated river systems.