Effect Of Total Dissolved Gas Supersaturated Water With Suspended Sediment On The Swimming Performance Of Grass Carp (Ctenopharyngodon Idella)

During flood season,the phenomenon of total dissolved gas supersaturation(TDG)easily occurs downstream of high dam.It has been confirmed that aquatic organisms(mainly fish)suffer from bubble disease due to TDG supersaturation.Their survival will be affected.This would be ruinous to the regulation and stability of aquatic ecosystem downstream of high dam.In recent years,due to the increasing electricity demand,the construction scale of high dams in China is expanding continuously.The problem of TDG supersaturation is becoming more and more serious.Therefore,in view of the serious impact of TDG supersaturated water on aquatic organisms downstream of high dam when flood discharge,it is urgent for scientific research in China to propose effective countermeasures.In addition,some studies have shown that the suspended sediment in the discharged water will also pose a threat to the normal activities and even the survival of aquatic organisms.And in practice,in the case of flood discharge,TDG supersaturated water downstream channel usually contains suspended sediment,which severely affects the survival of fish.The swimming performance of fish is an important way to ensure its normal survival activities,and the swimming ability is also a crucial index to evaluate the movement quality of fish in various activities.At present,domestic and foreign studies have mainly attach importance to the effects of suspended sediment or TDG supersaturation alone on the swimming ability of fish.Few studies have investigated the interaction effect of the two factors on the swimming ability of fish.Therefore,it has practical value to carry out the research to investigate the mechanism of the interaction effect of suspended sediment and TDG supersaturation on the swimming ability of fish.And it will provide valuable basic information for the formulation of the reservoir operation scheme of high dam during flood season and the reconstruction of the fishway downstream high dam.Grass carp,an economical fish,inhabiting the middle and upper reaches of the Yangtze River,was selected as the research object.Sediment with a median particle size of 108)was used to prepare the water mixed with suspended sediment.Through the indoor TDG supersaturated sediment-containing water circulation system,the mixture water of TDG supersaturation and suspended sediment was generated to be employed in the swimming ability test experiment of grass carp.The main results were as follows:(1)Under the experimental conditions of 50,100 and 150 mg/L suspended sediment,the absolute critical swimming speed(?U_crit)of grass carp was decreased by 7.02?7.84and7.86cm/s,respectively,compared with the 0 mg/L group.The absolute burst swimming speed(?U_crit)of grass carp was decreased by 9.95?11.51?13.90cm/s,respectively,compared with the 0 mg/L group.The relative critical swimming speed(?U_crit)of grass carp was decreased by 1.19?1.32?1.33TL/s,respectively,compared with the 0 mg/L group.The relative burst swimming speed(?U_crit)of grass carp was decreased by 1.73?1.97?2.35TL/s,respectively,compared with the 0 mg/L group.There was a negative correlation between the swimming ability of grass carp and suspended sediment concentration.(2)Under the interaction effect of the same TDG supersaturation level(135%)and vary suspended sediment concentrations,compared with the group of 50mg/L suspended sediment concentration,the decreasing values of absolute critical swimming speed of 100 and 150 mg/L concentrations were?U_crit:2.57?3.52cm/s,respectively,and?U_burst:2.70?5.61?6.60 and7.82cm/s,respectively.The swimming ability of grass carp decreased in conjunction with the increasing suspended sediment concentrations.Under the interaction effect of the same suspended sediment concentration and vary TDG supersaturation levels,compared with the group of 115%TDG,the decreasing values of absolute critical swimming speed of 120?135%TDG levels were?U_crit:4.68?9.66cm/s,respectively,and?U_burst:6.81?7.1?12.36?17.21cm/s,respectively.The swimming ability of grass carp decreased in conjunction with the increasing TDG supersaturation levels.The results indicated that in the interaction effect of TDG supersaturation and suspended sediment,the swimming ability of grass carp was negatively correlated with both TDG supersaturation and sediment concentration.(3)The interaction of TDG supersaturation and suspended sediment has no significant effect on the swimming ability of grass carp.In addition,the effect of TDG supersaturation on the swimming ability of grass carp was extremely significant,TDG supersaturation is the main influence factor.Suspended sediment is a secondary factor,in the TDG supersaturated water,the existence of suspended sediment will reduce the swimming ability of grass carp.