Publication date: 20211018: 59:13 Source: Journal of Lake Science, 20 16, 28 visits: 207 17.
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Algae control of silver carp and bighead carp in eutrophic lakes: controversy and understanding
Liuzhangqigen town
(School of Fisheries and Life, Shanghai Ocean University, Shanghai 20 1306)
2016-01-31received the manuscript; 20 16-02-02 received the revised draft.
Fund projects: public welfare industry (agriculture) special project (20 1303056), national major science and technology special project of water pollution control and treatment (2012zx07101-007), national natural science foundation project (3/kloc-0)
About the author: Liu Qigen (1965~), male, doctor, professor; E-mail:qgliu@shou.edu.cn。
The control direction of lake eutrophication in China is changing from pollution control to lake ecological restoration and management, and non-classical biological control technologies such as silver carp and bighead carp have attracted attention. However, there are two cases of success or failure in controlling algae in silver carp and bighead carp, which leads to excessive discussion on whether algae in eutrophic lakes can be controlled. This paper points out the possible reasons for the different experimental results of algae control between silver carp and bighead carp, and puts forward the understanding that can be obtained from the study of algae control between silver carp and bighead carp in order to provide reference for the management and protection of lake environment in China.
Key words: algae control of overgrowth of eutrophic silver carp and bighead carp in lakes
Controlling harmful algae in eutrophic lakes by silver carp and bighead carp: controversy and consensus
Liu Qigen, qgliu@shou.edu.cn, Zhang zhen
The control of lake eutrophication in China is shifting from pollution control to restoration and management of lake ecosystem. Non-traditional biological manipulation based on the role of silver carp and bighead carp in lakes has attracted people's attention. However, silver carp and bighead carp have both successful cases and failed cases in controlling harmful algae, which leads to differences on their application feasibility. This paper analyzes a large number of studies on the influence of silver carp and bighead carp on algae growth, points out the possible reasons for the different results of these case studies, and tries to reach a consensus on using silver carp and bighead carp to control algae overgrowth in eutrophic lakes. We hope this effort can play a role in the environmental management and protection of lakes in China.
Keywords: Eutrophication of Silver Carp and Bighead Carp in Lake, Controlling Pollution Algae by Cyanobacteria Bloom
Silver carp and bighead carp are the two most common freshwater economic fish in China, and they are also the largest aquaculture production in the world [1]. Silver carp, bighead carp, herring and grass carp are also called "four big fish", which play an important role in the development history of freshwater fishery in China. Silver carp and bighead carp often account for more than 40% of the fishing output in some lakes (for example, silver carp and bighead carp in Qiandao Lake in Zhejiang Province account for more than 50% of the total fishing output, and East Lake in Wuhan accounts for more than 90% [2]). Therefore, silver carp and bighead carp are undoubtedly the most influential dominant groups in China's lakes, and they are also the most remarkable characteristics that distinguish the structure of China's lake food web from foreign countries.
However, people's interest in silver carp and bighead carp is not limited to their fishery utilization value. Because silver carp and bighead carp mainly feed on plankton, the possibility of using silver carp and bighead carp to control algae overgrowth or cyanobacteria bloom in eutrophic lakes has already aroused widespread interest at home and abroad [4-6]. But people's understanding of whether silver carp and bighead carp can control algae has been controversial, and there is no * * * understanding so far. In fact, there are many studies on the ecological function or influence of silver carp and bighead carp at home and abroad, but unfortunately, these research results are often contradictory, which not only makes the scholars who carry out these studies unable to reach a unified understanding, but also makes the readers puzzled by these results. Therefore, the viewpoint of controlling the algae of silver carp and bighead carp has long existed widely at home and abroad. The existence of these viewpoints may make the positive effects of silver carp and bighead carp on the water environment not be properly utilized or their negative effects not be effectively avoided, or some improper water environment management policies may be introduced. Therefore, it is necessary to give a clear answer to this question as soon as possible, or form a * * understanding of China's water environment.
In order to help people answer the question whether silver carp and bighead carp can control algae, the author puts forward and tries to answer the following questions through the analysis of a large number of related studies at home and abroad: Why are the results obtained by different researchers so different, or even completely opposite? Through the analysis and summary of the existing research on algae control of silver carp and bighead carp, can we get a * * * understanding? If the existing evidence is not enough to form * * * knowledge, what kind of research should be carried out in the future to really help solve the problem (disagreement)?
Proposal and definition of 1 silver carp and bighead carp algae control scheme
Using silver carp and bighead carp to control the excessive growth of algae in eutrophic lakes was put forward after the eutrophication of lakes became more and more common, and gradually attracted people's attention. As early as 1970s 1980s, there were international studies on controlling algae by silver carp and bighead carp [4,8-65438]. At1980s [11-12], China began to pay attention to and study the algae control of silver carp and bighead carp. Excessive growth of algae, especially the outbreak of cyanobacteria bloom, is often regarded as the worst sign of lake eutrophication, which not only seriously affects the water quality of the lake, but also harms the lake ecosystem. Therefore, it is an important aspect of lake eutrophication control. Because silver carp and bighead carp can filter algae, whether they can be used to control the overgrowth of algae in eutrophic lakes has naturally become a very interesting topic for researchers at home and abroad.
The algae control of silver carp and bighead carp discussed in this paper refers to whether silver carp and bighead carp can be used to control the overgrowth of algae or prevent the outbreak of cyanobacteria in lakes where pollution sources have been basically controlled (that is, point source pollution has been effectively controlled, non-point source pollution and endogenous pollution will be the main influencing factors). It is difficult to control the excessive growth of algae only by stocking silver carp and bighead carp The existing understanding is that controlling pollution sources is the premise of controlling eutrophication. In lakes where pollution sources have been basically controlled, it is still necessary to use silver carp and bighead carp to control algae, because even if point source pollution is well controlled, its water quality may not be improved in time. These lakes may still cause abnormal algae growth or even cyanobacteria bloom due to a large number of non-point source pollution in the basin or endogenous pollution of the lakes themselves, so it may still be very necessary to prevent algae overgrowth and improve water quality through biological manipulation. This is also the main application scenario of algae control of silver carp and bighead carp in lakes in China, that is, algae control of silver carp and bighead carp should be a means of lake environmental management.
Experimental study on algae control of silver carp and bighead carp: two typical cases
There have been a large number of cases at home and abroad on algae control of silver carp and bighead carp. Xie Ping's "Silver Carp, Bighead Carp and Bloom Control" [7] gives many domestic and foreign research cases for the reference of interested readers. But these cases are not enough to eliminate people's differences of opinion on whether silver carp and bighead carp can control algae. In order to help people understand the algae control of silver carp and bighead carp as soon as possible. Because there are two cases of success and failure in algae control of silver carp and bighead carp, it is necessary to solve the difference between silver carp and bighead carp from both positive and negative aspects.
2. 1 silver carp and bighead carp failed to control algae.
The research of Professor Shi of Dalian Fisheries University and his colleagues is one of the earliest experiments to control the algae of silver carp and bighead carp in China. The study was carried out in May-July of 1982 [1 1], and eight 3 m3 (with an area of about 2 m2 and a depth of 1.5 m) on the bank of the reservoir were used. Group b was not fed. When the reservoir water was injected into the experimental pond, the average length of silver carp and bighead carp were 10.2 cm, and the densities were 0, 6, 18 and 36 /m3, respectively (the ratio of silver carp to bighead carp was 2: 1). Meanwhile, they are kept in the same cage in the reservoir area. The total length of silver carp and bighead carp is about 10 cm, and they are stocked at the densities of 0, 0.6, 65, 438+0.0 and 65,438+0.5 million fish per box (specification 7 m× 4 m× 65,438+0.8 m) respectively. The experiment was divided into two groups, C and D, and the indexes of hydrochemistry and aquatic organism composition were measured 65,438+0 times every five days. The sampling time is 15:00- 15:30. In the experiment of cage culture, the box is not washed and the water flow exchange is weak. The micro-current meter can't measure the flow rate. Before and after the cage experiment, the indexes of 1 hydrochemistry and aquatic organism composition were determined. The experimental period (cement pond and cage) is 20 days. The results show that the primary productivity, phytoplankton biomass and P/B coefficient of water body can be significantly improved by stocking silver carp and bighead carp. Among them, the change range of dense culture pond is greater than that of sparse culture pond. The biomass, yield and P/B coefficient of phytoplankton did not decrease due to the feeding of silver carp and bighead carp, but the attached algae were obviously more than those in the empty box without fish culture, and the biomass, yield and P/B coefficient of phytoplankton in the box were slightly higher than those outside the box. In addition, with the stocking density reaching a certain level, the phytoplankton in the water body is obviously miniaturized, and the dominant species have also changed obviously. Take group a as an example. The number of phytoplankton cells is 140× 104 /mg, while the number of phytoplankton cells reaches 2650× 104 /mg in the A2 pond with 36 cells /m3. With the increase of stocking density, the biomass of zooplankton decreases and becomes smaller, while the growth of fish deteriorates with the increase of stocking density. The experimental results show that.
Since then, Ruan, a researcher from the Institute of Hydrobiology, Chinese Academy of Sciences, and his colleagues have also conducted algae control research on silver carp and bighead carp in the laboratory aquarium near 194 [13]. They selected 12 60 L aquariums and divided them into three experimental groups (silver carp and bighead carp in the second group). Tap water filtered with activated carbon was added with an algae medium called WC, and the water depth was 3 1 cm. Inoculate the remaining mixed algae culture solution after tilapia experiment, and the initial inoculation density is 0.15×105 cells/L. Anodonta falcata, Nitzschia. , scenedesmus. Chlorella. , Chlamydomonas. Among them, oscillatoria accounts for more than 80%. In the third week after inoculation with algae, Daphnia magna was introduced, with the density of 22 Daphnia magna per cylinder. In the fourth week after inoculation with Daphnia magna, silver carp and bighead carp with the size of 2.5~3.5 cm were stocked, and the average stocking density was 65438±05g/m3. The experiment lasted until 2 1 week after silver carp and bighead carp were released. In order to make the inoculated algae grow, each aquarium is equipped with 5000~6000 lx illumination, 12 h/d, and the water temperature of the aquarium is controlled at about 25℃, and 1 aquarium is sampled every week for aquatic organisms and hydrochemical indexes. The nutrient supplement was gradually increased according to 1% ~5% of the consumption of WC medium, and the average phosphorus load during the experiment was 0.0061g/(m3 d). The experimental results showed that the density of Daphnia magna decreased and the density of phytoplankton decreased after silver carp and bighead carp were introduced into the micro-experimental ecosystem.