乌梁素海网围养殖鱼类的生态效应研究

Study on the Ecological Effect of Fish Enclosure Aquacultured in Uliangsuhai Lake

为探讨不投饵网围养殖鱼类对乌梁素海水生态的影响,于2016年4月-2018年10月对占水面积为55.33 km2(8.3万亩)的乌梁素海网围养殖区的放养模式、养殖产量进行了调查分析;在网围养殖区设置了3个采样点研究放养鱼类对沉水植物(水草)过度生长的控制效果并对水质状况进行了分析评价。研究表明:(1)2016年-2018年,网围区共放养规格为0.75~1.25 kg/尾的2龄草鱼种75万尾,重量60万kg,放养密度108.4 kg/hm2;放养规格为0.6~1 kg/尾的2龄鲢、鳙鱼种150万尾,重量96万kg,放养密度173.5 kg/hm2;鲢、鳙放养比例为40∶60。放养平均规格为0.05 kg/尾的中科3号鲫鱼10万尾,重量5000 kg;放养平均规格为0.5 kg/尾的黄河鲤1万尾,重量5000 kg;放养平均规格为10000只/kg的河蟹1.5亿只,重量1.5万kg,放养密度18072只/hm2;(2)2017年-2018年,共捕捞出水各种水生动物达266.5万kg;其中草鱼70万kg,占比26.3%;鲢、鳙140万kg,占比52.5%;鲤、鲫20万kg(含野生),占比7.5%;兰州鲇4万kg(野生),占比1.5%;河蟹22.5万kg,占比8.4%;秀丽白虾10万kg(野生)占比3.8%;综合鱼产量481.6 kg/hm2;(3)网围养殖区外现存沉水植物平均生物量6.8 kg/m2,网围养殖区内沉水植物平均生物量仅有0.74 kg/m2,放养鱼类有效的控制了水草生物量,大幅降低了围养区的沼泽化进程;(4)对2016年-2018年网围区水体溶解氧、氨氮、总氮、总磷、COD、BOD5等水化学指标浓度进行了监测,网围区水体溶解氧含量在各个时期均达到Ⅰ类水质,氨氮含量在各个时期均达到Ⅱ类水质,总氮含量在夏、秋季达到了Ⅴ类水质,春季为劣Ⅴ类,总磷含量在各个时期均达到Ⅲ类水质,BOD5含量在各个时期均达到Ⅵ类水质,COD含量在各个时期均为劣Ⅴ类水质。说明乌梁素海通过网围生态养殖,湖区水质整体得到改善,但存在COD含量超标问题。

To study the effect on lake ecological condition of natural enclosure fish cultivation without fish feed in Uliangsuhai Lake,the breeding method and the fish yield in enclosure aquaculture area of Uliangsuhai Lake were investigated in about 55.33 km2(83000 mu)from April 2016 to October 2018.Three sites were set up for sampling in the area to study the control effect on the over-growth of submerged plants(water weeds)by cultivation of the fish and water quality of the lake purified by it.The research showed that(1)the average stocking size in the enclosure area from 2016 to 2018 were 600000 kg of grass carp,which was about 750000 two-aged fish(0.75~1.25 kg per fish)and with the density of 108.4 kg/hm2,960000 kg of silver carp and bighead carp,which was about 1.5 million two-aged fish(0.6~1 kg per fish)and with the density of 173.5 kg/hm2 and 40∶60(silver∶bighead)ratio,5000 kg of Zhongke no.3 crucian carp,which was about 100000 fish(0.05 kg per fish),5000 kg of Yellow River carp,which was about 10000 fish(0.5 kg per fish),15000 kg river crabs,which was 10000 crabs/kg,total 150 million crabs and with the density of 18072 crabs/hm2.(2)a total of 2.665 million kg of aquatic product(481.6 kg/hm2)were yielded from 2017 to 2018,which were 700000 kg grass carp,accounting for 26.3%,1.4 million kg silver carp and bighead carp,accounting for 52.5%,200000 kg carp and crucian carp(including wild),accounting for 7.5%,40000 kg Lanzhou catfish(wild),accounting for 1.5%;225000 kg river crab,accounting for 8.4%;100000kg Xiuli white shrimp(wild),accounted for 3.8%;(3)compared with the biomass of submerged plants(6.8 kg/m2)out of the enclosure area,the submerged plants in the enclosure area was only 0.74 kg/m2,indicating that this kind of the management of fishery effectively controlled the accumulation of biomass of water weeds and significantly decreased the process of lake swamping in the enclosure area.(4)determination of the content of dissolved oxygen,ammonia nitrogen,total nitrogen,total phosphorus,COD,BOD5 and other water chemical indicated that from 2016 to 2018 based on the environmental quality standard for surface water(GB3838-2002),the content of dissolved oxygen in the enclosure area reached classⅠin each season,the ammonia nitrogen content reached classⅡin each season,the total nitrogen content reachedⅤclass in summer and autumn and was inferior toⅤclass in spring,the total phosphorus content reachedⅢclass in each season,the BOD5 content reached classⅣin each season,the COD content was inferiorⅤquality in each season within the enclosure area.The study demonstrated that the water quality in Uliangsuhai Lake within the enclosure was improved generally although the COD content exceeded the standard.