Study On Swimming Characteristics And Recovery Ability Of Grass Carp Under The Stress Of Total Dissolved Gas Supersaturated Water

Since the twentieth century,the construction and operation of high dams have brought some negative effects to downstream river health.During the food season,total dissolved gas(TDG)supersaturation occurs when the gas pressure exceeds atmospheric pressure downstream of the dam.TDG supersaturation seriously threatens the survival of aquatic organisms in rivers and leads them to suffer from gas bubble disease and increase mortality.According to previous research,TDG supersaturated water had influences on the tolerance,growth characteristics and biochemical effects of downstream fish.However,few studies have assessed the impact of TDG supersaturation on their swimming ability in China.Therefore,exploring the swimming characteristics and recovery ability of fish under the stress of total dissolved gas supersaturated water,which can provide an important reference for the protection of aquatic biodiversity and the operation of fishways.According to previous researches,juvenile fish are more susceptible to TDG supersaturated water.In this study,juvenile grass carp(Ctenopharyngodon idellus),an important commercial fish in China,was selected as the research objects to assess the effects of TDG supersaturated water with different TDG levels on the swimming ability of juvenile grass carp.Meanwhile,the recovery ability of swimming ability of fish after TDG supersaturated water stress was analyzed.The main results were as follows:(1)Juvenile grass carp subjected to TDG supersaturated water exhibited slight gas bubble disease(gill bleeding)and abundant abnormal behaviors(shaking body continuously,raising their heads out of the water,jumping out of the water).The probability of bubble disease symptoms and abnormal behaviors of juvenile grass carps were different at different TDG levels.(2)At 100%,105%,110%,115%,120%,125%,130% and 135% TDG levels,the critical swimming speed of the juvenile grass carp were 6.27 ± 0.92BL/s,6.16 ± 0.86BL/s,6.15 ±0.83BL/s,5.96 ± 0.98BL/s,5.83 ± 0.91BL/s,5.58 ± 0.97BL/s,3.99 ± 0.84BL/s and 3.52 ±0.82BL/s,respectively,while the burst swimming speed of the juvenile grass carp were 10.15± 0.41BL/s,9.83 ± 0.35BL/s,9.72 ± 0.46BL/s,9.58 ± 0.46BL/s,9.41 ± 0.47BL/s,9.30 ±0.35BL/s,9.10 ± 0.55BL/s and 8.87 ± 0.25BL/s,respectively.The results showed that both the critical swimming speed and the burst swimming speed of the experimental fish decreased with the increased TDG levels,especially high levels(>125% TDG).The TDG supersaturated water has a significant effect on the critical swimming speed of juvenile grass carp,but has no significant effect on the burst swimming speed.(3)After recovery for 1 h,the recovery ratios of critical swimming speed of juvenile grass carp subjected to TDG supersaturated water(115%,120%,125%,130% and 135%TDG)were 81.9%,70.0%,70.2%,76.5% and 75.7%,respectively,and the recovery ratios of burst swimming speed of juvenile grass carp were 91.4%,90.1%,85.1%,82.8% and 83.1%,respectively.After recovery for 2 h,the recovery ratios of critical swimming speed of juvenile grass carp were 82.9%,83.8%,84.6%,84.4% and 82.1%,respectively,and the recovery ratios of burst swimming speed of juvenile grass carp were 98.6%,93.7%,94.9%,98.9% and 96.3%,respectively.It indicated that with the increased recovery time,both the recovery ratios of critical swimming speed and burst swimming speed of juvenile grass carp increased significantly.When the recovery time of juvenile grass carps was short,the recovery ratios of burst swimming speed decreased with the increased TDG levels,and TDG supersaturated water with different levels had a great influence on the recovery ability of juvenile grass carp.Furthermore,when juvenile grass carp recover for a certain period of time,the recovery effect of their burst swimming speed was higher than that of critical swimming speed.