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Volume 46 Issue 2
Feb.  2022
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Blocking efficiency of electrified barrier for guiding juvenile grass carp (Ctenopharyngodon idella) by pulsed direct current with different electric parameters at different flow velocities

  • Corresponding author: LIU Guoyong, 278113027@qq.com
  • Received Date: 2020-07-30
    Accepted Date: 2020-11-23
    Available Online: 2021-03-29
  • The necessity for fish to migrate safely is a key requirement for the existence of many fish populations. Anthropogenic constructions, such as dams and weirs, that block rivers, make it difficult, if not impossible, for fish to reach their upriver spawning grounds. Also, these constructions are also very dangerous for fish moving down the river because dams are built associated with hydroelectric power station intakes where fish are injured or killed on the gratings, pump screens, and in turbine chambers. Mild fields of pulsed, direct current (DC) electricity have been used extensively in deterring invasive fish species as well as in reservoir fishery, but directional fish guidance using electric deterrence arrays to guide fish toward desirable passage locations or away from dangerous areas has received little attention. The effectiveness of the electrified barriers is quite variable and testing is often lacking for a variety of water velocity conditions. To explore the effects of different electric parameters of electrified barriers on the avoidance behavior of the juvenile grass carp C. idella with body length of (10.22±2.01) cm and body mass of (34.25±3.62) g, a double-row type of electrified barrier based on pulsed direct current electricity was established and orthogonal designed experiment of three factors, including pulse voltage, frequency and width, four levels was adopted to optimize the blocking performance of the electrified barrier under the static water condition. To explore the effects of water flow conditions on the blocking efficiency of electrified barriers using the optimized electric parameters recommended for static water conditions, three flow conditions at a generalized model of fishway entrance were utilized to test the attractive efficiency of fishway entrance. The results showed that, under static water conditions, the working condition 7 had the highest blocking rate (88.67±1.10)% and lower average stupefaction rate and that the factors affecting blocking efficiency are pulse voltage, pulse frequency and pulse width respectively. Determined by analysis of variance and multiple comparison, the optimal electric parameters under static water conditions for blocking efficiency were the pulse voltage of 160 V/m, the pulse frequency of 6 Hz and the pulse width of 16 ms. Under the optimal electric parameters, the experimental fish had minimal injuries when subjected to electrified barriers. By employing the optimum electric parameters recommended for static water conditions, the active electrified barrier can dramatically boost the aggregation rate and average retention time ratio at the fishway entrance when the channel velocity was 0.15 m/s. When the channel velocity was 0.25 m/s and 0.35 m/s, the aggregation rate and average retention time ratio with the active electrified barrier were not enhanced significantly compared with those in the inactive electrified barrier. Therefore, the recommended electric conditions for optimal blocking effect is to set the pulse voltage of 160 V/m, the pulse frequency of 6 Hz and the pulse width of 16 ms under static conditons. The attractive effects of fishway entrance could be enhanced by the active electrified barriers with the best flowing water velocity being 0.15 m/s. These results will have important reference significance for the practical engineering of the electrified barrier arrangement. The pulsed direct current electric systems have the potential to improve fish passage at anthropogenic barriers. Additional research should investigate the effectiveness at variable electric field voltage and various water flow velocities for fish of various sizes and shapes depending on the species and its ethology.
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    [12] 王岑, 王继保, 吴欢, 等. 不同位置和朝向的鱼道进口诱鱼效果[J]. 水产学报, 2020, 44(4): 681-689.Wang C, Wang J B, Wu H, et al. Attractive effects for different positions and orientations of fishway entrance[J]. Journal of Fisheries of China, 2020, 44(4): 681-689 (in Chinese).
    [13] 郑铁刚, 孙双科, 柳海涛, 等. 基于生态学与水力学的水电站鱼道进口位置优化研究[J]. 水利水电技术, 2018, 49(2): 105-111.Zheng T G, Sun S K, Liu H T, et al. Ecology and hydraulics-based study on optimization of location for fishway entrance of hydropower station[J]. Water Resources and Hydropower Engineering, 2018, 49(2): 105-111 (in Chinese).
    [14] 龚丽, 吴一红, 白音包力皋, 等. 草鱼幼鱼游泳能力及游泳行为试验研究[J]. 中国水利水电科学研究院学报, 2015, 13(3): 211-216.Gong L, Wu Y H, Bai Y B L G, et al. Experimental study on swimming capability and swimming behavior of juvenile grass carp[J]. Journal of China Institute of Water Resources and Hydropower Research, 2015, 13(3): 211-216 (in Chinese).
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    [17] 许明昌, 徐皓. 养殖池底层鱼类电脉冲捕捞装置设计与试验[J]. 南方水产科学, 2011, 7(3): 62-67. doi: 10.3969/j.issn.2095-0780.2011.03.011Xu M C, Xu H. Design and experiment of fishing device with electrical pulse for demersal fish in aquaculture pond[J]. South China Fisheries Science, 2011, 7(3): 62-67 (in Chinese). doi: 10.3969/j.issn.2095-0780.2011.03.011
    [18] 平慧敏, 吴永汉, 刘琼. 鱼在脉冲电刺激后产生昏迷反应试验的观察和分析[J]. 云南大学学报(自然科学版), 1998, 20(S1): 27-28.Ping H M, Wu Y H, Liu Q. Observation and analysis of the fish’s stupor reaction stimulated by pulse electricity[J]. Journal of Yunnan University (Natural Sciences), 1998, 20(S1): 27-28 (in Chinese).
    [19] Johnson N S, Miehls S. Guiding out-migrating juvenile sea lamprey (Petromyzon marinus) with pulsed direct current[J]. River Research and Applications, 2014, 30(9): 1146-1156. doi: 10.1002/rra.2703
    [20] Swink W D. Effectiveness of an electrical barrier in blocking a sea lamprey spawning migration on the Jordan River, Michigan[J]. North American Journal of Fisheries Management, 1999, 19(2): 397-405. doi: 10.1577/1548-8675(1999)019<0397:EOAEBI>2.0.CO;2
    [21] Chmielewski A, Cuinat R, Dembi N, et al. Fatigue and mortality effects in electrical fishing[J]. Polskie Archive of Hydrobiology, 1973, 20: 341-348.
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    [24] Parker A D, Glover D C, Finney S T, et al. Fish distribution, abundance, and behavioral interactions within a large electric dispersal barrier designed to prevent Asian carp movement[J]. Canadian Journal of Fisheries and Aquatic Sciences, 2016, 73(7): 1060-1071. doi: 10.1139/cjfas-2015-0309
    [25] 廖伯文, 安瑞冬, 李嘉, 等. 高坝过鱼设施集诱鱼进口水力学条件数值模拟与模型试验研究[J]. 工程科学与技术, 2018, 50(5): 87-93.Liao B W, An R D, Li J, et al. Numerical simulation and model test study on the hydrodynamic conditions of fish luring inlet of fish-crossing facility in high dams[J]. Advanced Engineering Sciences, 2018, 50(5): 87-93 (in Chinese).
    [26] 汪亚超, 陈小虎, 张婷, 等. 鱼道进口布置方案研究[J]. 水生态学杂志, 2013, 34(4): 30-34. doi: 10.3969/j.issn.1674-3075.2013.04.008Wang Y C, Chen X H, Zhang T, et al. Study on layout scheme of fishway entrance[J]. Journal of Hydroecology, 2013, 34(4): 30-34 (in Chinese). doi: 10.3969/j.issn.1674-3075.2013.04.008
    [27] 龚丽, 吴一红, 白音包力皋, 等. 鱼道进口水流对草鱼幼鱼上溯行为的影响研究[J]. 水利水电技术, 2016, 47(11): 89-93, 106.Gong L, Wu Y H, Bai Y B L G, et al. Study on impact of water flow at fishway entrance on migratory behavior of juvenile grass carp[J]. Water Resources and Hydropower Engineering, 2016, 47(11): 89-93, 106 (in Chinese).
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Blocking efficiency of electrified barrier for guiding juvenile grass carp (Ctenopharyngodon idella) by pulsed direct current with different electric parameters at different flow velocities

    Corresponding author: LIU Guoyong, 278113027@qq.com
  • 1. Hubei International Science and Technology Cooperation Base of Fish Passage, China Three Gorges University, Yichang 443002, China
  • 2. College of Hydraulic and Environment Engineering, China Three Gorges University, Yichang    443002, China
  • 3. Tibet Water Conservancy and Hydropower Planning Survey and Design Institute, Lasa    850000, China
  • 4. College of Biological and Pharmaceutical Sciences, China Three Gorges University, Yichang    443002, China

Abstract: The necessity for fish to migrate safely is a key requirement for the existence of many fish populations. Anthropogenic constructions, such as dams and weirs, that block rivers, make it difficult, if not impossible, for fish to reach their upriver spawning grounds. Also, these constructions are also very dangerous for fish moving down the river because dams are built associated with hydroelectric power station intakes where fish are injured or killed on the gratings, pump screens, and in turbine chambers. Mild fields of pulsed, direct current (DC) electricity have been used extensively in deterring invasive fish species as well as in reservoir fishery, but directional fish guidance using electric deterrence arrays to guide fish toward desirable passage locations or away from dangerous areas has received little attention. The effectiveness of the electrified barriers is quite variable and testing is often lacking for a variety of water velocity conditions. To explore the effects of different electric parameters of electrified barriers on the avoidance behavior of the juvenile grass carp C. idella with body length of (10.22±2.01) cm and body mass of (34.25±3.62) g, a double-row type of electrified barrier based on pulsed direct current electricity was established and orthogonal designed experiment of three factors, including pulse voltage, frequency and width, four levels was adopted to optimize the blocking performance of the electrified barrier under the static water condition. To explore the effects of water flow conditions on the blocking efficiency of electrified barriers using the optimized electric parameters recommended for static water conditions, three flow conditions at a generalized model of fishway entrance were utilized to test the attractive efficiency of fishway entrance. The results showed that, under static water conditions, the working condition 7 had the highest blocking rate (88.67±1.10)% and lower average stupefaction rate and that the factors affecting blocking efficiency are pulse voltage, pulse frequency and pulse width respectively. Determined by analysis of variance and multiple comparison, the optimal electric parameters under static water conditions for blocking efficiency were the pulse voltage of 160 V/m, the pulse frequency of 6 Hz and the pulse width of 16 ms. Under the optimal electric parameters, the experimental fish had minimal injuries when subjected to electrified barriers. By employing the optimum electric parameters recommended for static water conditions, the active electrified barrier can dramatically boost the aggregation rate and average retention time ratio at the fishway entrance when the channel velocity was 0.15 m/s. When the channel velocity was 0.25 m/s and 0.35 m/s, the aggregation rate and average retention time ratio with the active electrified barrier were not enhanced significantly compared with those in the inactive electrified barrier. Therefore, the recommended electric conditions for optimal blocking effect is to set the pulse voltage of 160 V/m, the pulse frequency of 6 Hz and the pulse width of 16 ms under static conditons. The attractive effects of fishway entrance could be enhanced by the active electrified barriers with the best flowing water velocity being 0.15 m/s. These results will have important reference significance for the practical engineering of the electrified barrier arrangement. The pulsed direct current electric systems have the potential to improve fish passage at anthropogenic barriers. Additional research should investigate the effectiveness at variable electric field voltage and various water flow velocities for fish of various sizes and shapes depending on the species and its ethology.

  • 在江、河中进行的筑坝活动对水生生态系统带来很多负面的影响,阻断了鱼类的自由迁徙,破坏了河流生态系统的连通性[1]。为了保证和促进鱼类的自由迁徙,一些江、河中建设了过鱼设施[2]。但目前国内外已建成的部分过鱼设施的运行效果并不理想,为此设计师们往往设置了一些辅助诱驱鱼措施来改善其运行效果,拦鱼电栅是其中有效的诱驱鱼措施之一[3]。另一方面,为了使鱼类远离涡轮机和泄洪道等危险区域,在涡轮机和泄洪道前方布置拦鱼电栅是一种有效的保护鱼类的辅助措施[4]

    利用鱼类对电流的反应来导鱼或者驱鱼已有100多年的历史,从最初的交流电到最近使用的脉冲直流电。由于脉冲直流电产生的电场是不连续的、电场极性也不发生改变,因此对人和鱼的伤害较小[5];但是脉冲直流电对鱼的生理效应最强,且断电后的持续作用时间最短,此外,脉冲直流电还可以大大节省功率[6],因此在电驱鱼的设施中脉冲直流电得到了广泛应用。尽管拦鱼电栅技术已发展了多年,但是主要的应用局限于水库渔业[7]、防止外来物种入侵[8]等领域,且多以工程实践和经验性成果为主,而将其应用于过鱼设施中保护本地鱼类资源的研究则很少。

    为了使脉冲直流电的拦鱼、导鱼作用更加高效,国内外学者展开了一系列相关的研究。例如,在河流中布设双频脉冲直流电的拦鱼电栅能阻拦海七鳃鳗(Petromyzon marinus)的上溯并将其导入陷阱,从而阻止海七鳃鳗大量入侵劳伦山脉五大湖[8]。Parasiewicz等[9]研制了一种可连续产生不均匀的低压(50~80 V)电场的拦鱼电栅NEPTUN,对14种不同大小鱼类进行实验测试表明,在流速小于0.2 m/s的水流条件下,NEPTUN能够对93.8%~98.2%的鱼类起到很好的阻拦效果。尽管拦鱼电栅被应用到阻拦海七鳃鳗[8]、虹鳟(Oncorhynchus mykiss)[10]等鱼类的迁移扩散,但是影响其有效性的因素、目标鱼类的种类和大小等方面仍然存在知识空白,尤其是如何合理设置拦鱼电栅的脉冲电压、脉冲频率等参数,既可以高拦鱼的效率、同时又不使鱼类受到损伤[8]。水流的改变不能影响水中电场的强度,但鱼类具有顶流的习性,在不同水流速度下,拦鱼电栅的驱鱼效果也不尽相同[9]。目前国内外对上述问题的研究还较少,鱼类在不同电学参数、不同流速下对脉冲直流电的响应行为值得进一步研究。

    四大家鱼是我国重要的鱼类资源。由于过度捕捞、水域污染、水利工程建设等原因,近年来其资源量明显下降[11]。因此,针对四大家鱼,特别是幼鱼,有必要开展针对拦鱼电栅对幼鱼行为影响方面的研究,并评价拦鱼电栅作为一种潜在的资源增殖保护设施,为鱼道等上行过鱼设施以及协助鱼类下行的行为导鱼设施的设计提供依据。本实验以草鱼(Ctenopharyngodon idella)幼鱼作为研究对象,采用自行设计的脉冲电压、脉冲宽度及脉冲频率可调节的脉冲发生装置,利用拦鱼电栅作为脉冲直流电的载体,在静水条件下通过3因素4水平的正交实验设计,得出针对草鱼幼鱼拦鱼效果最佳的电学参数;并在鱼道模型中通过放鱼实验进行验证,以探明不同河道流速对拦鱼效果的影响,以期为水利工程建设中拦鱼电栅的设置提供基础资料和参考依据。

1.   材料与方法
  • 草鱼幼鱼由宜昌渔场提供,体长(10.22±2.01) cm、体质量(34.25±3.62) g,暂养于三峡大学生态水利实验室,暂养缸规格直径2.5 m、高0.5 m、水深0.3 m的PVC圆形水槽。暂养7 d,待其生活状况稳定后开始进行实验,暂养水为曝气72 h以上的自来水,暂养期间持续曝气,水温(20.2±0.5) °C,每天16:00左右按照鱼体质量的2%投喂1次商品颗粒饲料,喂食后1 h采用虹吸的方法清除残饵,每天换水约1/4。

    在实验结束后,将实验鱼放入多个0.6 m×0.5 m×0.5 m (长×宽×高)、水深0.3 m的玻璃箱中观察和暂养,暂养期间持续曝气。每天16:00左右按照鱼体质量的2%投喂1次商品颗粒饲料,每天换水约1/4。

  • 静水实验装置包括实验水槽、拦鱼电栅、连接拦鱼电栅的脉冲发生器及监控设备(图1)。其中实验水槽规格为6.0 m×1.0 m×0.5 m,末端设有拦鱼网形成鱼类适应区,水深0.2 m。实验用水为曝气的自来水,电导率为210 S/m。拦鱼电栅用木制支架固定于实验水槽上方,采用能够产生与水流方向平行的电场线的双排式拦鱼电栅布置方式。每排拦鱼电栅采用3根电极管,电极管之间的距离为0.3 m,排电极之间的间距为0.5 m,电极管采用导电性能良好的不锈钢材质。其中,接近拦鱼网的一排电极管通过电线与脉冲发生器阳极相连接,另一排电极管与脉冲发生器阴极相连接。

    Figure 1.  Experimental device in static water

  • 参照西藏ZM水电站的相关参数,在室内修建一座鱼道模型,以1∶80的缩放比尺建造大坝(厂房与溢洪道)室内物理模型,以1∶10的缩放比尺建造鱼道室内模型[12]。概化模型包括矩形量水堰、上游过渡区域、穿孔花墙、电站厂房模型、溢洪道模型、位于岸边的鱼道一、位于河道中间的鱼道二、混凝土边壁以及为了调节河道水深的5组尾水闸门(图2)。概化模型长度为8.0 m,宽度为7.8 m,深度为0.65 m,布置于河道中央的鱼道二的长度设置为4.5 m。概化模型的实验用水为曝气的自来水,电导率为210 S /m,由供水系统提供,供水系统主要包括水泵、泵房水池、矩形量水堰、实验水槽和回水廊道等组成,构成了一个流速可调节的水循环系统。为了减少不必要的外界因素对实验结果的影响,关闭鱼道一进口,鱼道二设置一个位于末端的进口,开口方向与河道主流垂直,这样的鱼道进口布置方式能够产生更加适合鱼类上溯的诱鱼水流[12]。可通过调节鱼道进口的阀门来控制鱼道进口处的流速。在鱼道二的进口上游0.75 m采用双排式的电极布置方式布设拦鱼电栅,每排拦鱼电栅采用11根电极管,电极管通过塑料扎带、支架悬挂于河道上方。电极管间距为0.3 m,排电极之间的距离为0.5 m,电极管采用导电性能良好的不锈钢材质,电极管的长度为0.5 m,直径为6 mm,电极阵列布置图如图2所示。

    Figure 2.  Generalized diagram of the fishway

  • 静水实验中采用正交实验设计。选用脉冲电压(A)、脉冲频率(B)、脉冲宽度(C)作为考察因素,每个因素选择4个水平。根据之前进行的初步实验结果及相关研究,选取各因素的水平(表1)。

    编号
    no.
    因素与水平
    factors and levels
    对应的处理
    corresponding treatment
    ABC脉冲
    电压/(V/m)
    pulse
    voltage
    脉冲
    频率/Hz
    pulse
    frequency
    脉冲
    宽度/ms
    pulse
    width
    111120210
    122120412
    133120614
    144120816
    212160212
    223160414
    234160616
    241160810
    313200214
    324200416
    十一331200610
    十二342200812
    十三414240216
    十四421240410
    十五432240612
    十六443240814

    Table 1.  The design of L16(43) orthogonal experiment

    实验在8:00—13:00进行。实验开始前,从暂养池中随机选取5尾健康的草鱼幼鱼放入适应区适应20 min,然后撤去拦鱼网,用摄像机记录30 min内在拦鱼电栅未开启的情况下实验鱼通过拦鱼电栅的次数,作为对照组。开启并调节脉冲发生器至实验所需的脉冲电压、脉冲宽度及脉冲频率,然后再记录30 min内实验鱼通过拦鱼电栅的次数和实验鱼通过电场的行为反应。为防止实验鱼产生适应性而影响实验结果的可靠性,因此实验鱼不重复使用。每组实验重复5次,实验结束后将实验鱼捞起放入已编号的暂养缸中暂养观察10 d,每天记录实验鱼的成活率、体表出血程度、脊椎是否弯曲等。

  • 鱼道进口处的诱鱼水流流速为过鱼对象临界游泳速度的0.6~0.8倍时,此时鱼道进口的诱鱼效果最佳[13]。体长为(9.80±0.91) cm的草鱼幼鱼的临界游泳速度为(87.40±9.67) cm/s[14],因此鱼道进口处的吸引流速应控制在0.47~0.78 m/s为宜,本实验将鱼道进口处流速设置为0.5 m/s,河道的水深设置为0.15 m,分别设置了3种河道流速(0.15、0.25 和0.35 m/s)(表2)。实验前开启水泵和控温装置,利用循环水温控制系统调节水温,使水温维持在 (20.2±0.5) °C。通过调节水泵流速计和装置上鱼道进口的闸门开度使流速达到实验工况要求。实验用水为曝气的自来水,电导率为210 S /m。

    工况
    test conditions
    鱼道进口流速/(m/s)
    velocity at fishway entrance
    河道流速/(m/s)
    flow velocity of channel
    电学参数
    electric parameters
    脉冲电压/(V/m)
    pulse voltage
    脉冲频率/Hz
    pulse frequency
    脉冲宽度/ms
    pulse width
    0.50.15160616
    0.50.15000
    0.50.25160616
    0.50.25000
    0.50.35160616
    0.50.35000

    Table 2.  Test conditions for fishway entrance experiments

    实验在8:00—13:00进行。从暂养池中随机选取10尾健康的草鱼幼鱼,放于河道中鱼类适应区内适应20 min。开启视频监控系统,撤去拦鱼网,让实验鱼自主地顶流上溯(拦鱼电栅的电源关闭),用视频监控系统记录30 min内实验鱼的行为反应,作为对照组。从暂养池中再随机选取10尾健康的草鱼幼鱼,放于河道中鱼类适应区内适应20 min,然后开启拦鱼电栅(拦鱼电栅的电学参数设置为脉冲电压160 V/m、脉冲频率6 Hz、脉冲宽度16 ms),撤去拦鱼网,用视频监控系统记录30 min内实验鱼的行为反应。每种工况下的实验重复5次,实验鱼不重复使用。改变河道水流流速,重复上述实验步骤。实验结束后,捞起实验鱼,每种工况的实验鱼分别放入已编号的暂养池中观察10 d,观察并记录实验鱼的成活率、体表出血程度、脊椎是否弯曲等现象。

  • 通过视频统计实验鱼在拦鱼电栅未开启的30 min内通过拦鱼电栅的次数,以及开启拦鱼电栅后30 min内实验鱼通过拦鱼电栅的次数、尝试通过的次数及产生昏迷反应的次数。其中,当实验鱼接近拦鱼电栅的过程中、或游到拦鱼电栅的两电极之间,因受到电流刺激而逃离不穿过电场均记为尝试通过;昏迷反应定义为鱼体侧翻或身体失去平衡。

    通过率(i)定义为实验鱼在拦鱼电栅开启后30 min内的通过次数占未开启拦鱼电栅时30 min内实验鱼的通过次数的百分比。昏迷率(µ)定义为实验鱼产生昏迷反应的次数占未开启拦鱼电栅时30 min内实验鱼通过次数的百分比。以阻拦率(η)为指标表示拦鱼电栅对实验鱼的阻拦效率。阻拦率越高,通过率以及昏迷率越低,表示拦鱼电栅的阻拦效果越好。计算公式:

    式中,N为未开启拦鱼电栅时30 min内实验鱼通过拦鱼电栅的次数,T为开启拦鱼电栅后30 min内实验鱼通过拦鱼电栅的次数,S表示开启拦鱼电栅后30 min内实验鱼产生昏迷反应的次数。用单因素方差分析法析(One-Way ANOVA)分析拦鱼电栅开启前实验鱼通过拦鱼电栅的次数、拦鱼电栅开启后实验鱼通过拦鱼电栅次数、尝试通过次数以及产生昏迷反应次数之间的差异是否显著,统计值使用平均值±标准误(mean±SE)表示,P<0.05表示差异性显著。分别计算各实验组中的阻拦率、通过率、昏迷率的平均值,得到平均阻拦率、平均通过率和平均昏迷率。采用正交实验极差分析、方差分析、多重比较(SNK 法)等分析方法分析不同因素对平均阻拦率、平均通过率、平均昏迷率的影响,确定驱鱼效果最佳的电学参数组合,并将该最优组合应用于鱼道进口效率实验进行验证。

    将鱼道进口处半径r=1 m的扇形区域定义为鱼道进口的有效诱鱼区域(图2中灰色区域),当实验鱼受到鱼道进口水流的吸引作用而游入该片水域时,表示鱼道进口诱鱼水流成功诱鱼。将实验鱼在上溯过程中进入有效诱鱼区域内的诱集率(Rr)与鱼道进口平均停留时间比率(Pr)2个指标来评价鱼道进口的过鱼效率,其中:

    式中,Fc表示每组实验中实验鱼成功进入鱼道进口有效诱鱼区域的尾数,Fa表示每组实验中离开适应区、成功上溯的实验鱼尾数;Ti表示一组实验中成功上溯的某尾实验鱼在有效诱鱼区域停留的时间,T表示每组实验中实验鱼开始上溯到实验结束的时间,即30 min。

    通过像视频分析,统计拦鱼电栅未开启的30 min内鱼道进口的RrPr,以及拦鱼电栅开启之后30 min内鱼道进口的RrPr,并对所有的实验数据进行双因素方差分析,统计值使用平均值±标准误(mean±SE)表示。实验数据采用Excel 2003、SPSS 19.0 统计软件进行处理。

2.   结果
  • 拦鱼电栅开启之前,实验鱼在水槽中呈现自由游动的状态。当开启拦鱼电栅之后,位于拦鱼电栅附近的实验鱼惊慌失措地窜游,游向拦鱼电栅阳极或以接近爆发的游泳速度逃离水中电场至较远的区域。拦鱼电栅开启一段时间后,实验鱼以自由游动状态慢慢地游向拦鱼电栅,当靠近拦鱼电栅时部分实验鱼会立即改变方向远离拦鱼电栅;部分实验鱼会游向拦鱼电栅中间区域,以接近平行水中电场等势线的方向加速游过一段距离、然后掉头逃离水中电场。随着脉冲电压等电学参数的增加,少数实验鱼因受到水中电场的刺激作用而产生了昏迷反应,当关闭拦鱼电栅或者当实验鱼离开了水中电场作用范围后,实验鱼会清醒过来。实验结束后将实验鱼捞起放入暂养缸中分别暂养观察10 d,所有实验鱼的成活率均为100%,体表无出血、脊椎未出现弯曲等现象。

  • 在实验设计的16组不同电学参数的工况下,草鱼幼鱼的通过次数、尝试通过次数都显著低于未开启拦鱼电栅时的通过次数(P<0.05)。开启拦鱼电栅后草鱼幼鱼在工况一、二、三和四中的通过次数显著高于其他组(P<0.05)。草鱼幼鱼在工况十六中的昏迷次数最高,工况十三中的昏迷次数次之,2者的昏迷次数都显著高于其他工况(P<0.05)。在所进行的16组工况中,拦鱼电栅在工况七(脉冲电压160 V/m、脉冲频率6 Hz、脉冲宽度16 ms)下,对草鱼幼鱼的拦鱼效果最好,此时的阻拦率最高,通过率及昏迷率也相对较低 (图3)。

    Figure 3.  Times of experimental fish crossing, attempting to cross electrified barrier and producing stupefaction reactions

  • 脉冲电压、脉冲频率、脉冲宽度对拦鱼电栅阻拦率的极差分析结果显示,对于平均阻拦率而言,各因素的主次效应为脉冲电压>脉冲频率>脉冲宽度。当脉冲电压设置为160 V/m、脉冲频率为6 Hz、脉冲宽度为16 ms时,拦鱼电栅对草幼鱼的阻拦效果最优(表3)。

    指标
    indicators
    电学参数
    electric parameters
    指标总和
    the index summation
    极差
    range
    主次水平
    importance
    最佳组合
    optimum combination
    k1k2k3k4
    平均阻拦率/%
    average blocking rate
    脉冲电压/(V/m) (A) 74.00 87.93 84.28 76.75 13.93 A>B>C A2B3C4
    脉冲频率/Hz (B) 79.01 80.60 82.39 79.82 3.39
    脉冲宽度/ms (C) 80.67 80.60 80.17 81.00 0.83

    Table 3.  Range analysis of the effect of electrified barrier on fish-blocking rate

  • 为了检验脉冲直流电电学参数对平均阻拦率、平均昏迷率、平均通过率等指标是否有显著性影响,对正交实验结果进行方差分析(表4)。根据各因素的F值大小,影响顺序为脉冲电压>脉冲频率>脉冲宽度,此结论与主效应分析结果完全一致。3个因素中脉冲电压对平均阻拦率、平均昏迷率、平均通过率等3指标均有显著影响(P<0.05),而脉冲频率和脉冲宽度对平均阻拦率和平均昏迷率都无显著影响。脉冲电压、脉冲频率和脉冲宽度等3个因素对草鱼幼鱼的平均通过率都有显著影响(P<0.05)。

    指标
    indicators
    方差来源
    source
    Ⅲ型平方和
    type Ⅲ sum of squares
    自由度
    df
    均方
    mean square
    F
    F value
    P
    平均阻拦 average blocking rate 脉冲电压/(V/m) 433.456 3 144.485 16.883 0.002
    脉冲频率/Hz 25.075 3 8.358 0.977 0.464
    脉冲宽度/ms 2.587 3 0.862 0.101 0.957
    误差 51.348 6 8.558
    平均昏迷率 average stupefaction rate 脉冲电压/(V/m) 531.905 3 177.302 37.573 0.000
    脉冲频率/Hz 13.685 3 4.562 0.967 0.467
    脉冲宽度/ms 28.071 3 9.357 1.983 0.218
    误差 28.313 6 4.719
    平均通过率 average passing rate 脉冲电压/(V/m) 0.079 3 0.026 266.785 0.000
    脉冲频率/Hz 0.001 3 0.000 4.963 0.046
    脉冲宽度/ms 0.003 3 0.001 10.044 0.009
    误差 0.001 6 9.90×10−5

    Table 4.  Variance analysis of the effect of electrified barrier on fish-repelling

    为了确定最优阻拦处理的条件组合,分别对各因子进行单因素多重比较以确定不同水平间的差异显著性(表5)。结果表明,脉冲电压为160 V/m的阻拦率与脉冲电压为200 V/m的阻拦率差异不显著(P>0.05),但是160 V/m水平的昏迷率显著低于200 V/m 与240 V/m水平,因此最优脉冲电压条件为160 V/m,其次为200 V/m。根据阻拦率越高,通过率以及昏迷率越低,则拦鱼电栅的阻拦效果越好,因此,最优条件组合为A2B3C4,即脉冲电压为160 V/m、脉冲频率为6 Hz、脉冲宽度为16 ms。

    影响因素
    related factors
    处理
    treatments
    平均阻拦率/%
    average blocking rate
    平均昏迷率/%
    average stupefaction rate
    平均通过率/%
    average passing rate
    脉冲电压/(V/m) pulse voltage 120 74.07±3.19b 0.00±0.00c 25.93±3.19a
    160 86.72±1.48a 0.59±0.35c 12.69±2.17b
    200 84.28±1.98a 7.15±1.08b 8.57±0.79c
    240 76.75±3.17b 14.21±2.02a 9.04±1.16c
    脉冲频率/Hz pulse frequency 2 79.00±3.75 5.41±3.53 15.58±4.92a
    4 80.60±2.95 5.23±2.74 14.17±4.39ab
    6 82.39±3.15 4.37±2.77 13.24±3.75b
    8 79.82±2.83 6.94±4.63 13.24±3.39b
    脉冲宽度/ms pulse width 10 80.67±3.78 3.48±2.39 15.85±4.76a
    12 79.98±2.74 5.14±3.08 14.88±4.28a
    14 80.17±3.46 6.84±4.50 12.99±3.96b
    16 81.01±2.96 6.50±3.52 12.50±3.34b
    注:纵向小写字母不同表示同一因素的不同水平差异显著
    Notes: Different lowercase letters longitudinal indicate significant difference of the same factors’s at different level processing

    Table 5.  Multiple comparisons and statistics of three factors in the orthogonal experiment

  • 随着河道流速的递增,拦鱼电栅在开启前和开启后草鱼幼鱼在有效诱鱼区域内的诱集率均呈现出先增加后减少的趋势,但变化的比率均不显著(P>0.05)。当河道流速为0.15 m/s时,拦鱼电栅的开启能够显著提高草幼鱼的鱼道进口诱集率(P<0.05),而当河道流速为0.25、0.35 m/s时,开启拦鱼电栅能一定程度上提高草鱼幼鱼在有效诱鱼区域内的诱集率,但提升不显著(P>0.05)(图4)。双因子方差分析显示差异来源于拦鱼电栅的开启,开启拦鱼电栅后显著高于未开启拦鱼电栅(P<0.05),在实验所选取的流速范围内不同流速影响不显著(P>0.05),流速和拦鱼电栅开启之间的交互作用也不显著(P>0.05)(表6)。

    Figure 4.  Attraction rate of fish at fishway entrance at different channel velocities with electrified barrier on or off

    参数
    parameter
    方差来源
    source of variance
    Ⅲ型平方和
    type Ⅲ sum
    of squares
    自由度
    df
    均方
    mean square
    F
    F
    P
    诱集率
    aggregation rate
    拦鱼电栅开启与否 electrified barrier 1215.779 1 1215.779 9.305 0.006
    河道流速 environmental velocity 425.322 2 212.661 1.628 0.217
    拦鱼电栅×河道流速 electrified barrier × environmental velocity 174.370 2 87.185 0.667 0.522
    平均停留时间比率
    average retention time ratio
    拦鱼电栅开启与否 electrified barrier 212.534 1 212.534 4.016 0.056
    河道流速 environmental velocity 565.895 2 282.947 5.347 0.012
    拦鱼电栅×河道流速 electrified barrier × environmental velocity 57.177 2 28.589 0.540 0.590

    Table 6.  Two-way ANOVA of aggregation rate and average retention time ratio of C. idella behavioural tests under various electrified barrier and environmental velocity conditions

    在拦鱼电栅开启前,随着河道流速的递增,草幼鱼在鱼道进口的停留时间比率呈现持续增加的趋势,且当河道流速为0.25、0.35 m/s下的鱼道进口停留时间比率与0.15 m/s的鱼道进口停留时间比率相比,均显著提升(P<0.05)(图5)。拦鱼电栅开启之后,随着河道流速的递增,草鱼幼鱼的鱼道进口停留时间比率呈现先增大后减小的趋势,但相互之间差异性并不显著(P>0.05)。双因子方差分析显示,差异来源于河道流速的增加,开启拦鱼电栅对鱼道进口停留时间比率影响不显著(P>0.05),而流速对鱼道进口停留时间比率影响显著(P<0.05),流速和拦鱼电栅开启之间的交互作用也不显著(P>0.05)(表6)。当河道流速为0.15 m/s时,拦鱼电栅的开启能够显著提高草鱼幼鱼的鱼道进口停留时间比率(P<0.05),而当河道流速为0.25、0.35 m/s时,开启拦鱼电栅能一定程度上提高草鱼幼鱼的鱼道进口停留时间比率,但提升不显著(P>0.05)(图5)。通过视频分析结果发现,当河道流速为0.35 m/s时,草幼鱼受到水中电场的刺激作用后更多的是随着鱼道进口的诱鱼水流以及河道水流的冲击作用而游向河道下游,并在下游适宜区顶流。

    Figure 5.  Average retention time ratio of fish at fishway entrance at different channel velocities with electrified barrier on or off

    实验结束后将实验鱼捞起放入暂养缸中分别暂养观察10 d,所有实验鱼的成活率均为100%,体表无出血、脊椎未出现弯曲等现象。

3.   讨论
  • 脉冲式拦鱼电栅是以拦鱼电栅作为脉冲直流电的载体,通过在水中产生一个无“形”的电网以刺激鱼类神经、肌肉系统,当电流达到某一数值时,鱼类开始惊惶不安地窜游,企图逃离电场,以达到拦鱼、驱鱼的作用[15]。本研究中,静水条件下未开启拦鱼电栅时,实验鱼以自由游泳的状态穿越拦鱼电栅,且穿越次数较为频繁;开启拦鱼电栅之后,16种工况下的通过次数都显著低于未开启拦鱼电栅 (图3),实验鱼开始惊慌失措地窜游,说明实验鱼对水中电流比较敏感,部分实验鱼游向阳极并远离阴极或离开电场,这是因为鱼类在电场作用下有趋阳反应[16]。影响脉冲直流电驱鱼效果的电学参数主要有脉冲电压、脉冲频率和脉冲宽度。根据欧姆定律及电场原理,脉冲电压作为最重要的电学参数,直接影响水中电场的电流大小,也直接影响拦鱼效果以及人和鱼类的安全性[15]。本研究中的极差分析和方差分析结果表明,脉冲电压对拦鱼效果的影响最大(表3表4)。脉冲频率与脉冲宽度也影响鱼在电场中的反应,低频率、短脉冲时鱼类对脉冲直流电的反应较为敏感,然而并不意味拦鱼电栅的驱鱼效果更加高效一些[6]。各个电学参数的变化都会影响拦鱼电栅的拦鱼效果。例如许明昌等[17]发现,在低脉冲电场的工作条件下,当脉冲频率为10~20 ms、脉冲宽度为5~10 Hz时,驱鱼装置对底层鱼类有很好的驱赶作用。平慧敏等[18]指出脉冲宽度在15~20 ms、脉冲频率在5~14 Hz时,在脉冲电刺激下能使鱼产生昏迷反应,同时关闭脉冲电刺激一段时间后,鱼又能苏醒过来,不致使鱼类受到损伤。本研究发现,在脉冲电压设置为160 V/m、脉冲频率设置为6 Hz、脉冲宽度设置为16 ms时,静水条件下拦鱼电栅对草鱼幼鱼的拦鱼效果最佳,此时的平均阻拦率为88.67%±1.10%。同时,在这种电学参数的组合方式下,草鱼幼鱼的平均昏迷率也相对较低1.38%±0.98%,并且关闭拦鱼电栅一段时间后,草鱼幼鱼又能够苏醒,暂养观察10 d后,草鱼幼鱼的成活率为100%,体表无出血,未出现脊柱弯曲现象。这说明采用该电学参数下的拦鱼电栅并未造成鱼类的损伤。一些研究也得到了类似结论,采用合适的电学参数的脉冲直流电拦鱼电栅不会给鱼造成损伤。这可能是由于脉冲直流电是非连续的,鱼类有时间和空间调整自身行为,逃离脉冲电场,从而避免受伤[19-20]

  • 在阻拦鱼类下行,避免鱼类进入溢洪道、水轮机等危险区域的拦鱼电栅,布置在低流速的水流条件(小于0.3 m/s)下才能达到好的拦鱼效果,因为只有低流速才能保证鱼类有足够的时间对脉冲电流做出反应并逃离[9]。例如,在水流流速为0.15 m/s的区域内,用于拦导鲑进入鱼梯的拦鱼电栅有着80%的拦导效率,而在流速为0.45 m/s的区域内,拦导效率降低至62%[21];在美国亚基马河,当拦鱼电栅脉冲电压设置为125 V、脉冲频率设置为15 Hz、脉冲宽度设置为20 ms时,在0.2 m/s的区域内,拦鱼电栅对鲑幼鱼有着69%~84%的阻拦率,当流速条件改变至0.5 m/s时,阻拦效率降低至40%~53%[22]。本研究同样发现,在水流流速为0.15 m/s时,用于引导草鱼幼鱼进入鱼道进口的拦鱼电栅的拦导效果最好,而当流速而增加时拦导效率下降。

    水流速度的增加不能改变水中电场,但是本研究和其他多项研究[19, 21-22]都表明,随着水流速度的增加,使用脉冲直流电的拦鱼电栅其拦导效率会降低。因此,今后需要进一步研究水深、水的电导率、水流速度等变化时,如何优化拦鱼电栅的电场条件,实现高效率地拦导目标鱼类。

  • 依据是否有替代路径,拦鱼电栅可以分为两类,一类是阻拦外来鱼种上溯、入侵的拦鱼电栅,一般横跨整个河段,入侵鱼类没有其他通道、只有穿过拦鱼电栅才能上溯[23-24]。这种情况下,入侵鱼类会在夏季和秋季聚集在拦鱼电栅下游,不断尝试穿过拦鱼电栅,有些鱼类甚至被电击致死[23-24]。另一类拦鱼电栅,鱼类有替代的上溯通道(例如鱼道),这种情况下拦鱼电栅发挥拦导的作用[3],迫使鱼类进入替代路径。

    鱼道进口是鱼道工程的针眼。鱼道进口的位置、朝向及诱鱼水流的水力学特性等是影响鱼道进口过鱼效率的关键[12, 25]。能否采取适当的措施(例如集诱鱼水流),诱集目标鱼类到达进口区域是鱼道工程设计的关键[25]。对于水力发电的枢纽工程,通常将鱼道进口布置于水力发电厂下游尾水区域[26],而一些研究表明,鱼类往往更容易被电厂尾水的竞争流吸引而难以从鱼道进口进入鱼道,导致鱼道进口诱鱼效率低[26]。因此,鱼道进口附近可布设一些拦鱼和导鱼设施,有效提高鱼道进口的诱鱼效率。例如,长洲鱼道进口设置导墙,并在鱼道进口上游设置拦鱼电栅,极大增加了鱼道过鱼效率[3]。拦鱼电栅布置在主河道给鱼类提供一种厌恶、不利的刺激信号,迫使鱼改变迁移运动方向,从而提高鱼类进入人们预期的区域[8],例如鱼道进口的几率。本研究中,当河道流速为0.15 m/s时,开启拦鱼电栅能显著提高鱼道进口的诱集率和停留时间比率。而拦鱼电栅要发挥拦导效果,除了拦鱼电栅要有高的拦鱼效率之外,鱼道进口附近区域须有足够的吸引力。例如,鱼道进口水流流速适宜,鱼道进口附近增加诱鱼水流、避免回流区等[27]

    鱼类个体大小是影响拦鱼电栅感受性的重要因素[5]。个体越大,则在电场中实际感受的电压就越大。因此,相对于个体小的鱼而言,个体大的鱼只需要较低的电压就能产生明显的逃离或者昏迷行为[5]。本研究中的实验鱼个体较小,得到的电学参数仅适用于类似规格的草鱼幼鱼;若应用于其他规格的草鱼,以及水深、水的电导率等发生变化时,则需对电学参数进行进一步的调整和验证。

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