TDG过饱和高含沙水体对鲤幼鱼的影响

Effects of TDG Supersaturated Water and Suspended Sediment on Juvenile Cyprinus carpio

高坝泄洪后产生的总溶解气体(Total dissolved gas,TDG)过饱和含沙水体威胁着下游河道鱼类的生存。以鲤(Cyprinus carpio)幼鱼为实验对象,中值粒径为7μm的泥沙为实验用沙,开展不同规格鲤幼鱼受TDG过饱和含沙水体胁迫的耐受性实验。结果表明,实验开始后不久,鲤幼鱼出现较明显的异常行为和气泡病症状;在无沙和含沙量为1 500 mg/L的TDG过饱和(饱和度为125%、130%、135%)水体中,无沙水体第一批实验鱼[体长(6.40±0.10) cm、体重(5.80±0.20) g]的中位生存时间为14.3 h、10.3 h、9.1 h,含沙水体(1 500 mg/L)第一批实验鱼的中位生存时间为13.0 h、9.8 h、7.1 h,两者无显著性差异(P>0.05);含沙量为1 500 mg/L的TDG过饱和(饱和度为125%、130%、135%)水体中,第二批小规格实验鱼[体长(5.80±0.25) cm、体重(2.00±0.31) g]的中位生存时间为12.6 h、10.2 h、7.4 h,第三批大规格实验鱼[体长(8.50±0.57) cm、体重(9.50±0.48) g]中位生存时间为11.2 h、8.6 h、4.5 h,两者也无显著差异(P>0.05),不同规格实验鱼对TDG过饱和含沙水体的耐受性无明显差异(P>0.05)。即使含沙量达到1 500 mg/L,泥沙单独作用并未造成实验鱼异常或死亡,但高饱和度(135%)的过饱和TDG与泥沙共同作用对实验鱼影响较大,降低了实验鱼的中位生存时间(最小值为4.5 h)。

Water from high dam spillways leads to supersaturated total dissolved gases(S-TDG)and high suspended sediment(SS),threatening the survival of downstream fish.Although the number of high dams has increased,there are few reports available on the combined effects of S-TDG and high SS.In this study,the tolerance of Cyprinus carpio to this combination of stressors was investigated.Juvenile fish of different size(small and large)were exposed to S-TDG at saturations of 125%,130%and 135%,without SS(0 mg/L)and with SS(1 500 mg/L;average median diameter,7μm).During the exposure of each treatment group,abnormal activity,exposure symptoms,exposure time at death and death rate were recorded and median survival time calculated.C.carpio displayed abnormal behaviors and symptoms of gas bubble disease in the 125%,130%and 135%S-TDG groups.Response intensity increased with degree of TDG supersaturation,exposure time and fish size.Median survival times[average full length,(6.40±0.10)cm;average weight,(5.80±0.20)g]were,respectively,14.3 h,10.3 h and 9.1 h at S-TDG levels of 125%,130%,135%,without SS,and 13.0 h,9.8 h and 7.1 h with SS.There was not a significant difference between S-TDG treatments with SS and those without SS.At S-TDG levels of 125%,130%,135%,with SS,the respective median survival times of smaller fish[fork length,(5.80±0.25)cm;weight,(2.00±0.31)g]were 12.6 h,10.2 h and 7.4 h and,for larger fish[fork length,(8.50±0.57)cm;weight,(9.50±0.48)g],11.2 h,8.6 h and 4.5 h.The differences in median survival times between small and large fish were not significant.While SS(1500 mg/L)alone did not result in abnormal activity or death,the combined effect of S-TDG(135%)and SS decreased median survival time to 4.5 h.Our results provide a scientific basis for evaluating the effect of flood discharges on fish and supports efforts to protect aquatic organisms downstream from high dams.