Background

Total dissolved gas (TDG) caused by the rapid outflow of water from dams may threaten the survival of fish. However, few studies have assessed the impact of fish size on their tolerance to TDG supersaturation in the Yangtze River. To investigate the influences of fish size on the TDG supersaturation tolerance of fish, juvenile grass carp (Ctenopharyngodon idellus) of two sizes were subjected to TDG-supersaturated water at high levels (125%, 130%, 135% and 140%). Furthermore, varying flood flows may cause different TDG levels during the flood season. Fish may be subjected to low, chronic exposure to TDG before peak flooding occurs. However, TDG tolerance in fish subjected to high levels of TDG-supersaturated water after chronic exposure is rare. To further investigate the tolerance of juvenile grass carp subjected to acute exposure after chronic TDG exposure, juvenile grass carp were exposed to high levels of TDG-supersaturated water (125–140%) after receiving 96 h of chronic exposure (115% TDG).

Results

In the single acute exposure and multiple exposures (acute exposure after chronic exposure), similar abnormal behaviours and symptoms of gas bubble disease (GBD) were observed in the juvenile grass carp subjected to the TDG-supersaturated water. No abnormal behaviour or mortality was observed in fish in the first chronic exposure of the multiple-exposure treatment. As the TDG level increased, the mortality of the large and small juvenile grass carp increased. The median lethal time (LT₅₀) for the large juvenile grass carp was 36.55, 21.75 and 6.37 h at 130%, 135% and 140% TDG levels, respectively, while the LT₅₀ value of the small juvenile grass carp was 88.13, 61.49 and 35.88 h at the same TDG levels, respectively. In addition, the LT₅₀ value of juvenile grass carp during acute TDG exposure after chronic exposure was 26.22, 7.54 and 5.34 h at 130%, 135% and 140% TDG levels, respectively.

Conclusion

The tolerance of juvenile grass carp decreased with increasing TDG levels. The large juvenile grass carp had weaker tolerance to TDG-supersaturated water than the small juvenile grass carp. In addition, compared with juvenile grass carp subjected to single acute exposure, juvenile grass carp subjected to multiple exposures exhibited lower tolerance and were more vulnerable to the adverse effects of TDG.

中文翻译：

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总溶解气过饱和度对草鱼耐性（Ctenopharyngodon idellus）的影响。

背景

大坝中水的快速流出所导致的总溶解气体（TDG）可能威胁鱼类的生存。但是，很少有研究评估鱼的大小对其在长江中对TDG过饱和的耐受性的影响。研究鱼的大小对鱼，少年草鱼（Ctenopharyngodon idellus）的TDG过饱和耐受性的影响两种尺寸的）均以高浓度（125％，130％，135％和140％）的TDG过饱和水处理。此外，在洪水季节，不同的洪水流量可能导致不同的TDG含量。在洪灾高峰发生之前，鱼类可能会长期处于较低的TDG暴露水平。但是，长期暴露于高水平TDG-过饱和水的鱼类对TDG的耐受性很少。为了进一步研究在长期TDG暴露后急性暴露的草鱼的耐受性，在接受96 h长期暴露（115％TDG）后，将草鱼暴露于高水平的TDG过饱和水（125–140％）。

结果

在单次急性暴露和多次暴露（慢性暴露后的急性暴露）中，在经过TDG超饱和水处理的幼草鱼中，观察到相似的异常行为和气泡病（GBD）症状。在第一次多重接触治疗的慢性暴露中，未在鱼类中观察到异常行为或死亡率。随着TDG含量的增加，大小幼鱼的死亡率增加。在TDD水平为130％，135％和140％时，大型少年草鱼的致死时间（LT ₅₀）分别为36.55、21.75和6.37h，而小型少年草鱼的LT ₅₀值为88.13、61.49。在相同的TDG水平下分别为35.88小时。此外，LT ₅₀ 长期暴露后，TDD急性暴露时，幼鱼的平均价值分别为26.22、7.54和5.34h，分别为130％，135％和140％。

结论

幼草鱼的耐受性随TDG水平的升高而降低。大型幼草鱼对TDG过饱和水的耐受性要弱于小型幼草鱼。另外，与单次急性暴露的幼年草鱼相比，多次暴露的幼年草鱼显示出较低的耐受性，并且更容易受到TDG的不利影响。