Biological Control Against Cyanbacterial Bloom In Aquaculture Pond

Pond culture, the main way of aquaculture in China, plays an important role in the fishery production. The ecological conditions in aquaculture pond are very complicated. The requirment of high fishery production brings many problems, including eutrophication, galgal-bloom, and water pollutions, which restrict the healthy development of aquaculture. These problems are side-results from the measures currently and widely used for raising of economic benefit in aquaculture pond, including high stocking density and excess feeding and fertilization. The cyanobacteria in such ponds are common, wide spreading, adaptable, and strongly reproductive. Blooming cyanobacteria have a high consumption of oxygen, decrease the transparency of water, bring weakened immune system to the aquaculture animals, and cause high economic loss on the whole aquaculture industry. What’s more, Microcystis sp. produces toxin, which not only infectes aquaculture animals directly, but also threatens the health and lives of human. Therefore, the biological control against cyanobacteria in aquaculture pond and the improvement of ecological environment in pond water are important for the sustainable and healthy development of aquaculture.In this study, the control effects against cyanobacteria by aquatic animals (Lymnaea sp.), microbe (EM bacteria), beneficial algae (chlorella), aquatic plant (duckweed) in single and multiple ways were quantitatively investgated in laboratory. Based experimental results in lab, the enlarged volume of open water body was involved to simulate the conditions of aquaculture ponds, the optimal recruiting doses of Lymnaea sp. and addition volumes of EM were investgated sp.to achieve a better and synthetic controlling effect against cyanobacteria. Thisstudy aims to propose an applicable and economic resolution for controlling cyanobacterial bloom in aquaculture ponds, with the green and safe improvement of water quality and without no secondary pollutions. The results of present study possess ecologic significance. The main experimental results of this study are as follows.(1) In the experiment of the effect of Lymnaea sp. against several kinds of cyanobacteria. Lymnaea sp. was found efficiently controlling Microcystis aeruginosa, Anabaena flosaguas. Aphanizomenon flosaquae, Oscillatoriaceae and Nostocaceae. Taking Microcystis aeruginosa as an example, the densities of algae cells in the control groupsp. and the treatment group were same of 3.4×106 Cell·mL-1 at the beginning,. The density of algae cells in the control group increased to 5.9×106 Cell·mL-1 after 6 days, while intact algae cells were not observed in the treatment group. Twenty days later, the intact algae cells were still undetectable under the microscope from the treatment water. Therefore, Lymnaea sp. addition eliminated cyanobacteria during short time, and inhibited relapse of algal growth. In addition, addition of same density of Lymnaea sp. adults into the same density of Aphanizomenon flosaquae as those in the experiments of Microcystis aeruginosa, the algae cells became undetectable after 4 days, which is shorter than 6 days for Microcystis aeruginosa. It indicates that Lymnaea sp. control more efficiently against Aphanizomenon flosaquae than Microcystis aeruginosa. The feasibility and applicability of using Lymnaea sp. control algae bloom were then verified.(2) In the experiments of using aquatic EM bacteria, the growth of cyanobacteria was enhanced and subsequently inhibited with the increase of aquatic EM bacteria density in the case of without carbon source addition. The inflection point was influenced by medium concentration, algae species, and initial densities of algae cells. And also, aquatic EM bacteria was more efficiently against filamentous algae including Oscillatoriaceae sp., Anabaena flosaguas, and Nostocaceae sp. than Microcystis aeruginosa.. For example, the growthes of Microcystis aeruginosa cultured in 20% BG11 were not significantly inhibited by aquatic EM bacteriawith addition volumes of 2 mL,4 mL, and 8 mL, and were efficiently controlled by addition of 16 mL and 32 mL aquatic EM bacteria. The growthes of Oscillaiariaceae sp. cultured in 50% BG11 were all affected at ceartain extents by the addition of 2 mL,4 mL,8 mL, and 16mL aquatic EM bacteria, no matter the complete inhibitions were not observed. The growthes of Anabaena flosaguas and Nostocaceae sp. cultured in 100% BG11 were all inhibited by addition of 2 mL,4 mL,8 mL, and 16mL aquatic EM bacteria.(3) Under the condition of adding glucose as carbon source, aquatic EM bacteria significantly controlled blooming cyanobacteria, and the efficiency of which was enhanced with increase of glucose addition. Microcystis aeruginosa cultured BG11 were significantly inhibited by addition of 2 mL of aquatic EM bacteria in the presence of additional carbon source of 0.1 g,0.25g,0.5g,0.75g, and 1g glucose, and the efficiencies of which were enhanced by the increase of glucose addition. The controlling efficiencies against Oscillatoriaceae sp. cultured in BG11, by in the presence of 1 g glucose addition were enhanced by the increasing addition volume of aquatic EM bacteria from 1 mL,2 mL.4 mL,8 mL, until 16mL.(4) Under the condition in the absence of additional carbon source, the growthes of beneficial algae of Chlorella ellipsoidea were not affected by addition of 2 mL,.4 mL,8 mL, and 16 mL aquatic EM bacteria. But with addition of certain amount of glucose as carbon source, remarkable promotion onthe growthes of Chlorella ellipsoidea by aquatic EM bacteria was observed. In the se experiments, The results indicated that 2mL of aquatic EM bacteria remarkablely prompt the growth of Chlorella ellipsoidea, the efficiencies of which were enhanced by the increased glucose addition of 0.1 g,0.25 g,0.5 g,0.75 g, and 1g.(5) From the experiments on Lymnaea sp. and aquatic EM bacteria jointly controlling algae, it was found that the joint treatments achieved better controlling efficiencies than single treatments of same numbers of Lymnaea sp. or same addition volumes of aquatic EM bacteria, no matter with or without additional carbon sourcesp.. And the addition of Lymnaea sp. efficiently prevented oxygen deficit, water turbidity increase, and stink caused by excessive growthes of aquatic EM bacteria. These results indicates that Lymnaea sp. working together with aquatic EM bacteria is priorto anyone of them alone.(6) In the experiment of Lymnaea sp. cooperated with aquatic EM bacteria, the optimal additions of Lymnaea sp. and aquatic EM bacteria sp.were affected by the concentrations of medium, the densities of algal cells, water volumes, culture conditions, and so on. These factors interact with each other, and affect water quality. The balance among them maintains a good quality of water. After several experiment, it was found that Microcystis aeruginosa cultured in BG11 with density of 1.8×106 Cell·mL-1 was efficiently and economically controlled by the addition of 2.5g/L Lymnaea sp. conbined with 3.3mL/L aquatic EM bacteria and 0.6g/L glucose, and resulted in a good water quality.(7) In the experiments of the cooperation by chlorella and aquatic EM bacteria to control algae in laboratory scale, it was found that cooperating controlling method performed weakly against certain density of Microcystis aeruginosa by competing eutrophy. But the tendency of the higher densities of the chlorella contributing the higher efficiencies was clear. Base on the controlling effects against algae and economy, the proportion of the density ratio between chlorella microcystis aeruginosa is 1:1.(8) In the experiments using the various biological control methods, including Lymnaea sp.. duckweed, aquatic EM bacteria, Lymnaea sp., with duckweed. Lymnaea sp. with aquatic EM bacteria, and chlorella,. the respective dosage of each species was set based on preliminary results. The results indicate that the methods using Lymnaea sp.. duckweed, aquatic EM bacteria. Lymnaea sp. with duckweed.Lymnaea sp. with aquatic EM bacteria, and chlorella worked well to control against Microcystis aeruginosa except for regrowth in later period being observed in the experimental of aquatic EM bacteria..sp.sp. The ranking of the efficiencies was:Lymnaea sp. +aquatic EM bacteria (carbon source provided)> Lymnaea sp.+duckweed> Lymnaea sp.> chlorella> aquatic EM bacteria(carbon source provided). So the cooperation of Lymnaea sp. (1.25g/L) and aquatic EM bacteria (1.25g/L) performed with the best effect. The aquatic EM bacteria(carbon source provided) had almost no effect while Lymnaea sp.+aquatic EM bacteria(carbon source provided) remarkably controlled the growth of algae, and the dosages for each group is rational.(9) In the experiments that simulating aquaculture environments with the cyanbacterial bloom,10 fish tanks of 65×50×40 cm(lengthx×width×height) containing 65 L of Microcystis aeruginosa were used. A control group (T) was Microcystis aeruginosa only, another control group (T+Y) was with addition of fish, an experimental group (T+L) was with addition of Lymnaea sp.. an experimental group(T+L+Y) was with addition of fish and Lymnaea sp., an experimental group (T+EM) was with addition of aquatic EM bacteria, an experimental group (T+EM+Y) was with addition of aquatic EM bacteria and fish, an experimental group (T+P+L) was with addition of Lymnaea sp. and duckweed, an experimental group (T+P+L+Y) was with addition of fish, Lymnaea sp. and duckweed, an experimental group (T+EM+L) was with addition of Lymnaea sp.sp. and aquatic EM bacteria, the last experimental group (T+EM+L+Y) was with addition of fish, Lymnaea sp. and aquatic EM bacteria. During the experiments, the growthes of aquatic organisms in each group have no significant difference.. With addiion of Lymnaea sp. (0.075g/L), aquatic EM bacteria (0.5mL/L, glucose 0.5g/L), each treatment group had a obvious effect against algal growth. When Lymnaea sp.sp. was used, of the reduced dosage of Lymnaea sp. (0.075g/L) still achieved clear inhibition against algae in addition to the decrease of the concentration of N and P in water. The treatment with aquatic EM bacteria (0.5mL/L) with addition of glucose (0.5g/L) inhibited the algal growth distinctly. The controlling effect of same gosage of aquatic EM bacteria was quite weak in previous experiments using 2 L water but was significant in present experiment using 65 L water. It indicates that the dosage of aquatic EM bacteria could decrease in large water body to achieve same controlling efficiency. Addition of duckweed had an efficient effect againstthe growth of Microcystis aeruginosa, the effect of which was more stable and clear than only that of adding Lymnaea sp. only. That Lymnaea sp.sp. worked with aquatic EM bacteria achieved stable controling effect against cyanobacteria and better water quality.