Biological control experiment of excess propagation of Cyclops for drinking water security

Available online at www.sciencedirect.comJOURNAL OF.. ScienceDirectSCIENCESI JESCN11-26291~ DEEJoumal of Environmental Sciences 19(2007) 290 294ww.jesc.c.cnBiological control experiment of excess propagation of Cyclopsfor drinking water securityLIN Tao42", CUI Fu-yi2, LIU Dong-mei21. College of Environmental Science and Engineering, Hohai University, Nanjing 210098, China. E-mail: hit. lintao@ sina com2. School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, ChinaReceived 30 April 2006; revised 17 August 2006; accepted 4 September 2006AbstractCyclops of zooplankton propagated excessively in eutrophic water body and could not be effectively inactivated by the conventionaldisinfections process like chlorination due to its stronger resistance to oxidation. In this study, an ecological project was put forward forthe excess propagation control of Cyclops by stocking the filter-feeding fishes such as silver carp and bighead carp under the conditionof no extraneous nutrient feeding. The results of experiments with dfferent stocking biomass showed that the propagation of Cyclopscould be controlled efectively, and the water quality was improved simultaneously by impacting on nutriment level and planktoncommunity structure at proper stocking density of 30 g/m3 of water. The growth of Cyclops may not be efectually controlled withlower biomass of fish (10 g), and the natural food chain relation may be destroyed for Cyclops dying out in water while the intensestocking of 120 g per cubic meter of water. In addition, the high predator pressure may accelerate supplemental rate of nutients frombottom sediments to water body to add the content of total nitrogen and phosphorus in water.Key words: flter-feeding fishes; Cyclops; zooplankton; biomanipulation; water treatmentIntroductionof Cyclops shall be restrained and the water quality willbe restored following the consumption of the interiorRecent years in China, Cyclops of zooplankton exces-nutrient in water body by fish. The studies showed thatsively propagated in water bodies, especially in reservoirsthe food habit of fish had an important influence onand fresh lakes for drinking water source (Cui et al,the biomanipulation to control Cyclops propagation. Th2002). Cyclops have stronger resistance to oxidation, sobiomanipulations on plankton of omnivorous Cyprinusit could not be effectively killed by conventional disinfec-carpio and herbivorous Ctenopharyngodon idellus weretion like chlorination (Lin et al, 2004). In addition, theless effective than that of filter-feeding fishes, silver carpmotility of Cyclops made it easily penetrate sand filtersand bighead carp (Liu et al, 2004). But the biomanipu-into clear water tank in the waterworks, even municipallation of silver carp or bighead carp was limited to someservice pipe. Adult Cyclops, with body length of oneextent due to the respective food habit under conditionto several millimeters, may be caught by naked eye toof single stocking. So the experiment of poly-culture wasbring consumers unsanitary sense and may become diseasecarried out to investigate the biomanipulation of silver carptransmission medium as the host of pathogenic parasite,and bighead carp at diferent stocking density. In this study,like schistosome and eelworm, to threaten human healththe top-down influence on physicochemical environment(Olajide and Sridhar, 1987). The researches showed thatand Cyclops control of feeding fish, silver carp and bigheadthe overfishing resulted in the lack of fish in water body.carp, was studied by poly-culture.The superior consumer in food chain, fish died out torelease Cyclops from predator pressure and to sharply1 Experimental equipment and methodspropagate with a huge survival space (Cui et al, 2002).In this particle, the biological technique was put for-Eight water tanks with the volume of 1.2 m3 (theward, other than the traditional biomanipulation, to controldimensions of length, breadth and height were2, 5 and 1.2the excess propagation of Cyclops. The core idea is tom respectively) were used in the experiment and the depthutilize the biomanipulation of fish to control excess prop-of water was 1.1 m. As light source the fuorescent bulbsagation of Cyclops by stocking fish under condition of中国煤化工;00 Ix and irradiationno extraneous nutrient feeding. The excess propagationtimeer together with somesanitMHCN M H Gnts were added intoProject supported by the Hi-Tech Research and Development Programwater tanks to form experimental water-body and proper(863) of China (No. 2002AA601140). *Corresponding author. E-mai:hit. lintao@ sina.com.quantities of river mud was added to compose sedimentsNo.3Biological control experiment of excess propagation of Cyclops for drinking water security291of experimental system, in which the concentration ofwater condition. But the death of fish occurred during thenutrients was kept at eutrophic level. After water qualityexperiment because of the rapid drop of dissolved oxygenwas stabilized for a week, algae inoculated from schooland the abundance of algae began to increase. Only underlaboratory, which were mainly represented by Microcystiscondition of 30 g/m' of water, the biomanipulation of fishand Nostoc of Cyanophyta, Scencdesmus of Chlorophytawas atained a perfect effect with Cyclops level of less thanand Melosiraceae of Bacillariophyta, was added into the1 ind./L and the drop of algae abundance.tanks, i.e, the experimental water-body. After 3 weeks,Both silver carp and bighead carp belong to filter-Cyclops as well as Protozoa and rotifer sampled from thefeeding fish living in the upper layer of water body. TheyErlongshan Reservoir were inoculated into water tanks toare the special predators to feed on plankton and close inform the artificial ecosystem. The culture of Cyclops in thethe ecological niche of biology. But for food, silver carpmicrocosms has been for 2 weeks under no fish condition.is prone to prey on phytoplankton with the size of 15-A microcosms was used as the blank experiment and 50 μm like algae and a part of zooplankton as Copepodaothers were stocked with silver carp and bighead carp.(Smith, 1985; Li, 1993). The feeding object of bigheadEach experiment was processed along control one withcarp is mainly the zooplankton with the size of 40-110 pumtwo water tanks. The stocking density were 10, 30 andand few algae. The detection results of gut substance of120 g/m3 of water respectively, and the biomass betweenfish showed that the algae with larger scale as Microcystissilver carp and bighead carp was in a weight ratio of 7:3.in the microcosms was first captured by silver carp andThe water temperature was controlled in about 25+2°C andbighead carp was prone to prey on zooplankton and hadthe losing water due to natural evaporation and samplingobvious control effect on Cyclops (Fig.2). Such phe-was periodically refilled according to the water qualitynomenon has been proven by the experiments to controlof microcosms. One liter of mixed water was randomlycyanobacterial water bloom utilizing filter-feeding fishessampled from water tank without agitating the deposit in(Xie, 1996; Starling, 1993). So the poly-culture of silverthe bottom of the tank. Algae and Cyclops fixed by Lugolscarp and bighead carp not only efectively controlled theliquid were determined by microscopic count method andexcess propagation of Cyclops but avoid the appearanceother analytical examinations were conducted accordingof algae abundant growth due to the biomass reduction ofto standard methods. The experiment has been carried outzooplankton such as Cyclops.for 8 weeks. The experimental results were attained by theThe stocking density of fish plays an important roleaverage of datum from the same experiment.during the biomanipulation under condition of no extrinsicnutrients. The growth of Cyclops may not be effectually2 Results and discussioncontrolled with lower biomass of fish, 10 g, and the naturalfood chain relation may be destroyed for Cyclops dying out2.1 Biological control effect on Cyclopsin water while the intense stocking of 120 g/m3 of water.The varieties of plankton community after the stockingThe biomanipulation aimed to restore the ecological bal-of fishes are shown in Fig.1. As can be seen, the growthance and control the abundance of Cyclops to the naturallevel of under 1 ind./L. The feasible project is not only toof Cyclops was controlled to different extent due to thecontrol the excess propagation of Cyclops, but also to keepprey of filter-feeding fishes, silver carp and bighead carpthe natural food chain relation in favor of the stabilization(Fig.1a). At the end of experiment, the abundance ofof ecosystem. The extinction of Cyclops breaks away fromCyclops was still at higher level of 5 ind.,/L in the micro-the original intention of biological control and may resultcosms with the stocking density of 10 g/m3 of water, andin unforeknowable ecological problems.similarly the growth of algae has gradually risen (Fig. 1b). .In addition, the rapid drop of dissolved oxygen hasCyclops vanished from water soon and the growth of algaeshown that the amount of oxygen produced by photosyn-was controlled to some extent due to the intense preythesis of algae could not offset that of the consumption byaction of fish under the stocking density of 120 g/m3respiration of fish and other plankton under the stocking-◆-10g/m’++-30g/m'-+120g/m’-*Blankcontrolota3.「t1.55中0t1.0中国煤化工fYH.CNMHG 8Time (week)mme (weeK)Fig. 1 Varieties of the abundance of Cyclops (a) and algac (b).292LIN Tao et al.Vol. 192.2 Change of the community structureThe species composition of plankton in each micro-cosms varied with the change of abundance. The resultsare shown in Table 1. The algae species presented fromdominant Cyanophyta before the stocking of fishes todominant Bacillariophyta at the end of experiment withthe stocking density of 30 g/m'. The species compositionof algae was less infuenced by stocking 10 g/m3. Theproportion of phytoplankton represented on an averageFig. 2 Residua of Cyclops (间) and algae (b) in the gut of bighead carp.in the microcosms with 120 g/m'. As for zooplankton,the numbers of protozoa and rotifer increased and that ofCyclops was still at a higher level by the stocking density-◆-10g/m’-▲-.120g/m'of 10 g/m3. The abundance of Cyclops decreased with the1030 g/miBlank controlincrease of stocking biomass so that the prey object of fishchanged from Cyclops to protozoa and rotifer, the number)上王8of which in other two microcosms was less than that of theone with the stoking biomass of 10 g/m3.There was enough food for fishes under lower stockingdensity of 10 or 30 g/m3. According to size -fficiencyhypothesis, the large-scale plankton may be preferentiallyselected as food by fishes (Brooks and Dodson, 1965). Theanalysis of the fore-gut substance of fish further provedthat Cyanophyta with larger scale in the microcosms werefirst captured by silver carp and bighead carp was proneto prey on zooplankton. The results are shown in Table 2.The priority to prey on Cyclops and Cyanophyta of fishesFig. 3 Varieties of dssolved oxygen contentresulted in the amounts of those to low level so that the liv-ing space and prey pressure of other plankton were greatlyreleased as to the rapid growth. The fullness in the fore-gutdensity of 120 g/m3 of water condition (Fig.3). It mayof silver and bighead carp in the microcosms with stokingresult in negative effect on the stabilization of water qualitybiomass of 120 g/m3 was obviously lower than that of otherand ecosystem.two ones. Moreover, the fullness of fish fore- gut underTable 1 Vareties of plankton composition in ecosystem before and after the stocking of fishExperiment beginningExperiment end10 (g/m3)30(g/m3) 120 (g/m2)Blank10(g/m3) 30(g/m3) 120 (g/m3) BlankPhytoplankton (%)Cyanophyta5)26(602133315?Chiorophyta.3Bacillariophyta53Others)Zooplankton (nd/L) Cylops1830Protozoa370019301106300Rotifer43032132Experiment end is the time when fish dying in the microcosms with biomass of 120 g/m3, the percentage of phytoplankton represented by numberpercentage.Table 2 Comparison of the plankton composition and the fullness in the fore-gut of silver and bighead carp between diferent microcosms afterthe experimentSilver carpBighead carp30 (g/m3)120 (g/m3)Ratio of Phytoplankton to zooplanton1.491.313.620.230.180.724731Chlorophyta34292835Baciarophyta11142740Zooplankton (%)Cyclops7719中国煤化工812YHC NMH GiFullness (%)1..50.1.01.40.4The percent represented by number percentage.No.3Biological control experiment of excess propagation of Cyclops for drinking water security93condition of 120 g/m3 was also lower than that of natural of orthophoshate indicated the elevation of metabolismone in the actual water body, which meant that the fishes level (Table 3). The drop of granular phosphorus in thewere of hunger status. The lack of food increased the preymicrocosms of 30 g/m' showed that the ecosystem mayof fish on other plankton such as Bacillariophyta, Protozoa defer the eutrophication of water body but that of theand rotifer so that the composition of phytoplankton in the microcosms of 10 g/m3 was increased due to the poorgut of fish had no obvious distinction and zooplankton was control effect on phytoplankton (Boers et al, 1991).mainly composed of Protozoa and rotifer.But for higher stocking density as 120 g/m3, the nutrientelement became the limiting factor to the growth of fish2.3 Change of total phosphorus and total nitrogenunder condition of no extraneous nutriment feeding, inAs is well known, the eutrophication of water body iswhich the catabolism was dominant in the life activity ofmainly caused by the accumulation of nutrients such as silver carp and bighead carp. So the content of phosphorusnitrogen and phosphorus. The amount and variable ten- in fish organism was decreased at the end of experiment.dency of nutrients play an important role in the eutrophic"he high predator pressure may stimulate the growthcourse. The effects on the nutrient level before and after of other plankton and accelerate supplemental rate ofthe stocking of fish are shown in Fig.4. As can be seen, nutrients from bottom sediments to water body as to addthe concentration of total nitrogen and total phosphorus inthe content of total nitrogen and total phosphorus in water.the microcosms with the stocking of 10 and 30 g/m3 wasAs can be seen in Table 3, the final content of depositionalbetter than that in the ecosystem of 120 g/m', in which the phosphorus was less than that of experiment beginning inconcentration of nutrients was increased.the microcosms with stocking density of 120 g/m3. In ad-The varieties of nutrients are the result of the coopera-dition, there was obvious gradient distribution of nutrientstion of metabolism activity of aquatic organisms (Kitcheil,in the microcosms of 120 g/m3 and the concentration of1979). The results of phosphorus distribution in water body total nitrogen and total phosphorus in lower water wereand gut substance of fish showed that the nutients may not1.5 and 4 times than that in upper one respectively. Therestrict the biomanipulation of fishes under condition of concentration of total phosphorus arrived at 0.33 mg/L inlower biomass of 10 or 30 g/m3 due to the adequate food. the interface between substrate and water body at the endThe function of biomanipulation may be fully attainedof experiment. But in the other microcosms, the distinctionto convert the nutrients to living matter of fish itselfof nutrient concentration is about of 20%. The higherand the utility rate of nutrient was higher than that of nutrient load caused the rapid growth of algae after thedischarge by the catabolism of fish, which resulted in the death of fishes and may accelerate the deterioration ofdrop of nutrient content. At the end of experiment in thewater quality.wo microcosms, the phosphorus in fish organism wasSo the lower stocking density of silver carp and bigheadincreased and the content raise of depositional phosphorus carp is favor of utilizing nutrient during biomanipulationshowed that the ecosystem is in favor of restraining thein case of no extraneous food feeding. The experimentalrelease of phosphorus from sediment and reducing the ecosystem might be collapsed as a result of higher stockingrenew velocity of bottom nutrients. The concentration drop biomass due to the excessive prey.0.20.50.101.0 tTime (week)Fig. 4 Varieties of total mitrogen content间) and total phosphorus content (b).Table 3 Distribution of phosphorus in the difterent microcosms (mg/L)Experiment beginningExperiment end10 (g/m3)30 (g/m3)120 (g/m)Blank30 (/m3)120 (g/m3)Total phosphorus0.160.170.13中国煤化工0.10.18Granular phosphorus0.050.060.03Orthophoshate0.11YHCNMHG.120.07Depositional phosphorus124.42117.53 .136.24122.18T35.18136.27111.28128.22Phosphorus in fish organism 23.6469.61290.5242.34101.52287.32294LIN Tao et al.Vol. 193 Conclusionson biological control of the water fea of zooplankton in rawwater[]. Journal of HIT, 34(3): 399- 403.It is feasible to control the excess propagation of Cy-Kitcheil J F, 1979. Consumer regulation of nutrient cycling[J].clops by the poly-culture of silver carp and bighead carpBioscience, 29: 28 -34.and the method of fish biomanipulation may provide anLi Q, 1993. The infuence on plankton community of silvercarp[J]. Ecology Jourmal, 13: 30- -37.effective approach to resolve the danger to the drinkingLin T, Cui F Y, Liu D M et al, 2004. Full-scale study of removalsecurity from Cyclops.effect on Cyclops of zooplankton with chlorine dioxide[].The poly-culture density of silver carp and bighead carpJourmal of Environmental Sciences, 16(5): 746-750.play an important role during biomanipulation in case ofLiu D M, Cui F Y, Lin T, 2004. Preliminary study on biolog-no extraneous nutrient addition. The excess propagation ofical control of cyclops of zooplankton in drinking waterCyclops could be controlled effectively and also the watersource[J]. Journal of HIT, 11(2): 121-125.quality was improved simultaneously by proper stockingOlajide I, Sridhar M K, 1987. Guineaworm control in an endemicdensity. But the ecosystem might be collapsed as a resultarea in western Nigeria[J]. Aqua AQUAAA, 6: 333- 339.of higher stocking biomass.Smith D W, 1985. 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