Gas bubble trauma of Schizothorax prenanti at various life stages induced by total dissolved gas supersaturation

Total dissolved gas supersaturation (TDGS), commonly resulting from dam discharge, poses significant threats to fish survival by inducing gas bubble trauma (GBT) in downstream populations. Understanding the sensitivity of fish to TDGS during developmental stages is critical for evaluating survival risks during flood seasons. This study investigated the adverse effects of TDGS on three life stages-eggs, larvae, and juveniles-of the endemic fish Schizothorax prenanti (S. prenanti) in the upper Yangtze River. After hatching in 120 % and 130 % TDG levels, both eggs and larvae exhibited severe GBT symptoms with survival rates declining to 70 % and 77 % respectively, compared to 88 % in the control group. Hatching rates also dropped significantly to 66 % and 59 %, compared to 84 % in the control group. Larvae exhibited a marked reduction in body length at TDG levels above 120 %, while heart rates increased significantly at TDGS levels above 110 %. Juveniles subjected to 120 % and 130 % TDGS showed extensive GBT symptoms, with median lethal times of 92 and 35 h, respectively. After 35 h of exposure, juveniles in the 130 % TDGS group showed significant reductions in active metabolic rate (AMR), standard metabolic rate (SMR), and factorial aerobic scope (F-AS), while critical swimming speed (U_crit) and burst swimming speed (U_burst) remained unchanged compared to the control group. In terms of S. prenanti exposed to 130 % TDGS, U_crit and U_burst significantly declined when survival rate dropped to 25 %, while AMR, SMR, and F-AS exhibited significant changes prior to mortality occurred. Moreover, AMR, SMR, and F-AS in juveniles were more vulnerable to TDGS than U_crit and U_burst. These findings enhance the understanding of TDGS-induced stress on developing fish and support the development of ecological management strategies for TDG during flood seasons.