Effects of a Filter-Feeding Fish [Silver Carp, Hypophthalmichthys Molitrix

Freshwater Biology (2002) 47, 2337–2344

Effects of a ﬁlter-feeding ﬁsh [silver carp, Hypophthalmichthys molitrix (Val.)] on phyto- and zooplankton in a mesotrophic reservoir: results from an enclosure experiment

ROBERT J. RADKE and UWE KAHL Institute of Hydrobiology, Dresden University of Technology, Dresden, Germany

SUMMARY 1. Silver carp, Hypophthalmichthys molitrix (Val.), feeds on both phyto- and zooplankton and has been used in lake biomanipulation studies to suppress algal biomass. Because reports on the effects of silver carp on lake food webs have been contradictory, we conducted an enclosure experiment to test how a moderate biomass of the ﬁsh (10 g wet ) weight m 3) affects phytoplankton and crustacean zooplankton in a mesotrophic temperate reservoir. 2. Phytoplankton biomass <30 lm and particulate organic carbon (POC) <30 lm were significantly higher in enclosures with silver carp than in enclosures without fish, whereas Secchi depth was lower. Total copepod biomass declined strongly in both treatments during the experiment, but it was significantly higher in fish-free enclosures. Daphnid biomass was also consistently higher in enclosures without fish, although this effect was not significant. However, the presence of fish led to a fast and significant decrease in the size at maturity of Daphnia galeata Sars. Thus, the moderate biomass of silver carp had a stronger negative effect on cladoceran zooplankton than on phytoplankton. 3. Based on these results and those of previous studies, we conclude that silver carp should be used for biomanipulation only if the primary aim is to reduce nuisance blooms of large phytoplankton species (e.g. cyanobacteria) that cannot be effectively controlled by large herbivorous zooplankton. Therefore, stocking of silver carp appears to be most appropriate in tropical lakes that are highly productive and naturally lack large cladoceran zooplankton.

Keywords: biomanipulation, enclosure experiment, Hypophthalmichthys molitrix (Val.), plankton, silver carp

positive effects of silver carp (Miura, 1990; Wu et al., Introduction 1997; Domaizon & De´vaux, 1999; Fukushima et al., The use of the ﬁlter-feeding silver carp, Hypophthal- 1999). Four main factors can probably explain the michthys molitrix (Val.), as a biomanipulation tool to inconsistent results: (1) the stocking level of silver reduce phytoplankton biomass in lakes and reservoirs carp (Domaizon & De´vaux, 1999); (2) the initial remains controversial (Costa-Pierce, 1992; Starling zooplankton species pool (Starling et al., 1998; et al., 1998; Domaizon & De´vaux, 1999). While Starling Fukushima et al., 1999); (3) the initial phytoplankton et al. (1998) list 14 successful studies, others found no species pool (Datta & Jana, 1998) and (4) temperature conditions (Fukushima et al., 1999). All of the suc- Correspondence: Robert J. Radke, Institute of Hydrobiology, cessful experiments have in common the fact that they Dresden University of Technology, Mommsenstr. 13, 01062 were performed under eutrophic or hypertrophic Dresden, Germany. E-mail: [email protected] conditions where nuisance algae blooms ought to be

2002 Blackwell Science Ltd 2337 2338 R.J. Radke and U. Kahl suppressed and large or colonial algae (mainly as roach, Rutilus rutilus (L.), the dominant native cyanobacteria) were the predominant phytoplankton planktivore (Radke, unpublished data). Thus, the aim forms. The stocking with silver carp was considered of this study was to test the effect of a moderate successful in these cases, because the reduction of density of silver carp on the phytoplankton and cyanobacteria such as Microcystis spp. was the only crustacean zooplankton community while excluding important goal or because an overall reduction of the influence of other planktivorous fishes. phytoplankton biomass was achieved because small algae, which cannot be effectively removed by silver Methods carp (Herodek et al., 1989; Dong & Li, 1994; Vo¨ro¨s et al., 1997), were unable to build up high biomass The study was performed in mesotrophic Saidenbach within the time frame of the studies, resulting in an Reservoir, Saxony, Germany. The reservoir is primar- overall reduction of phytoplankton biomass. ily used for drinking water supply and to a limited Large herbivorous cladocerans, such as Daphnia extent for recreational fishing. The reservoir has a spp., are used more commonly than filter-feeding fish surface area of 1.46 km2, a mean depth of 15.3 m and a to reduce phytoplankton biomass in eutrophic lakes, maximum depth of 45 m. The mean annual concen- because Daphnia have high community filtration rates tration of total phosphorus declined from 25 to ) (Sterner, 1989). Success of biomanipulation strategies 15 lgL 1 within 2 years after the use of phosphate- fostering Daphnia grazing might be limited, however, free detergents became compulsory in 1990 and it has if phytoplankton community structure shifts towards remained stable since (Horn, Horn & Paul, 1994; Horn large inedible algae or if Daphnia are preyed upon et al., 2001). by fish or invertebrates (Gliwicz & Pijanowska, Six cylindrical enclosures, 1 m in diameter and 1989; Reynolds, 1994; Benndorf, 1995; Drenner & 12 m deep, were made of transparent polyethylene Hambright, 1999). Silver carp, together with large and stabilised with four stainless steel rings to prevent cladocerans, might reduce total phytoplankton bio- collapsing. The bottom of the enclosures was covered mass effectively, but have also been shown to with a 30-lm mesh gauze. The enclosures were hung suppress herbivorous zooplankton (Kajak et al., 1975; from a floating aluminium frame attached to the Opuszynski, 1979; Domaizon & De´vaux, 1999). Con- bottom of the reservoir. They were positioned in the sequently, Smith (1993) suggested using a series of centre of the main basin above a depth of 30 m. alternate ponds stocked with either silver carp or The enclosures were filled with unfiltered lake water large zooplankton as an approach to reduce phyto- by pulling the folded enclosures up from a depth of plankton biomass in wastewater treatment ponds. For 12–15 m 1 week before the start of the experiment. On lakes, Domaizon & De´vaux (1999) proposed a thresh- 22 June 1999, three enclosures were randomly selected ) old density of silver carp of 8 g wet weight m 3 and each stocked with two silver carp. Individual ) (200 kg ha 3) below which negative effects on herbi- biomass was 48.1 ± 6.7 g (mean ± 1 SD). The resulting vorous zooplankton should be minimised and bene- initial biomass in enclosures with fish was ) ficial effects on phytoplankton yet be effective. 10.2 ± 1.4 g m 3 and the final biomass was 10.1 ± ) We performed an enclosure experiment in a meso- 1.5 g m 3. We chose this biomass level, because it is ) trophic reservoir used for drinking water supply. close to the threshold value of 8 g m 3 found by Silver carp had been stocked in this reservoir, and a Domaizon & De´vaux (1999). The remaining three number of others in eastern Germany, in the late 1980s enclosures served as controls with no fish. to improve water quality (seston concentration). After Enclosures were sampled twice a week until 16 the stocking, the summer mean cladoceran biomass July. Water temperature was measured with a digital (almost entirely Daphnia galeata) decreased in the probe at depth intervals of 1 m. Water samples for the reservoir (Horn & Horn, 1995) and mean phytoplank- analysis of total phosphorus, particulate organic ton biomass remained unchanged (Horn, Paul & carbon (POC) and phytoplankton biomass were taken Horn, 2001). Although the decrease in cladoceran at 2-m intervals from the entire water column with a biomass was apparently correlated with the stocking 2-m tube sampler and mixed before taking subsam- of silver carp, this decrease might have been related to ples. Phosphorus concentrations were determined other planktivorous fish species in the reservoir, such according to standard methods (Institut fu¨ r

2002 Blackwell Science Ltd, Freshwater Biology, 47, 2337–2344 Effects of silver carp 2339 Wasserwirtschaft Berlin, 1986). The concentration of less than 0.5 C. On day 1 of the experiment, no POC <30 lm was determined with a carbon analyser significant differences in any of the measured varia- C-200 (LECO, St Joseph, MI, U.S.A.) after passing 250– bles was detected between control and treatment 500 mL of water through a 30-lm mesh screen and enclosures (Table 1). Total phosphorus concentrations filtering both size fractions on pre-ashed (500 C) declined during the experiment simultaneously in fish Whatman GF ⁄F filter (Whatman, Maidstone, UK) and no-fish control enclosures (Fig. 1), and repeated- under gentle vacuum (200 mbar). The 30-lm size measures ANOVA revealed neither significant differ- threshold for POC and phytoplankton fractions was ences between treatments nor sampling dates used, because it corresponds to the maximum particle (Table 2). Secchi depth was significantly higher (up size that is effectively filtered by D. galeata Sars to 2 m) in the no-fish enclosures than in the fish (Burns, 1968), the dominant cladoceran species in enclosures (Table 2). While the biomass of phyto- Saidenbach Reservoir (Horn & Horn, 1995). plankton <30 lm was significantly higher in the fish Phytoplankton was preserved with Lugol’s iodine enclosures, no difference was found in the biomass of solution immediately after sampling. Cells were the size fraction ‡30 lm. During the first week of the counted under an inverted microscope and sized to experiment, the biomass of the larger phytoplankton derive biovolumes from appropriate geometric shapes fraction declined strongly in both treatments and (Arbeitsgemeinschaft Trinkwasser e.V. Arbeitskreis subsequently remained low except for 1 day where Biologie, 1998). Biomass (wet weight) was calculated higher biomass levels were found in the no-fish ) assuming a wet weight density of 1 g cm 3. Crusta- enclosures. Concentrations of POC <30 lm were cean zooplankton was sampled by making vertical significantly higher in the fish enclosures than in hauls over the entire water column with a plankton no-fish enclosures. Although daphnid biomass was net of 100 lm mesh size, 25 cm in diameter and always higher in the controls (apart from the first day equipped with a flow meter. Samples were immedi- of the experiment), differences were not significant. ately preserved in sucrose-formaldehyde (3%) solu- Similar to daphnid biomass, copepod biomass tion. Taxa were counted in three subsamples and at decreased in both treatments over time, with no-fish least 100 specimens of D. galeata and 50 for all other enclosures showing a significantly higher biomass. taxa were measured. Biomass (wet weight) was The effect of fish on total crustacean biomass was calculated with length–mass regressions according slightly higher than the effect on daphnid biomass, to Bottrell et al. (1976) and size at maturity (SAM) of but it was not significant either (Table 2). Other D. galeata was determined as the smallest egg carrying cladocera, including Diaphanosoma brachyurum female in a sample. (Lievin), Bosmina spp. and Chydorus spp., accounted A t-test was performed to test for significant for <2% of the total crustacean biomass. The SAM of differences between treatments (fish presence versus D. galeata remained >1.1 mm in no-fish enclosures, absence) of all measured variables at the start of the but declined to values <0.9 mm in fish enclosures. experiment, and repeated-measures ANOVA was per- This highly significant change led to differences in formed to test for effects of fish presence and time on SAM of more than 0.4 mm between treatments on two seven sampling dates. Statistical analysis was per- sampling dates. formed with STATISTICA (StatSoft Inc., Tulsa, OK, U.S.A.). Discussion

Our results show that total phytoplankton biomass Results could not be reduced by silver carp at the chosen Surface temperature ranged from 16.6 C at the start moderate biomass level. The inability of silver carp to of the experiment to 20.0 C at the end. The lake was filter particles <10 lm effectively has been observed in stratified (thermocline at 8 m at the start of the several experimental studies (Herodek et al., 1989; experiment and 11 m at the end) and the temperature Smith, 1989; Dong & Li, 1994; Vo¨ro¨s et al., 1997) and difference between the water surface and enclosure explains why this fish species was unable to suppress bottom ranged from 6.5 to 7 C. Differences in total phytoplankton biomass in other studies (Miura, temperature between the lake and enclosures were 1990; Lieberman, 1996; Wu et al., 1997). In our

2002 Blackwell Science Ltd, Freshwater Biology, 47, 2337–2344 2340 R.J. Radke and U. Kahl

Table 1 Response variables (means ± 1 Variable Treatment Mean ± SD t-Value P-value SD) measured on the first day of the experiment (22 June 1999) in triplicate Secchi depth (m) NF 6.2 ± 0.4 1.0 0.37 enclosures with fish (F) and control F 6.0 ± 0.0 enclosures without fish (NF). t- and )1 Total phosphorus (lgL ) NF 8.4 ± 2.1 2.53 0.06 P-values of t-test (d.f. ¼ 4) F 14.0 ± 3.2 Particulate organic NF 0.46 ± 0.01 0.61 0.57 ) carbon <30 lm (mg L 1) F 0.50 ± 0.12 Biomass of phytoplankton NF 0.21 ± 0.08 0.44 0.69 ) <30 lm (mg L 1) F 0.18 ± 0.07 Biomass of phytoplankton NF 0.08 ± 0.01 1.48 0.21 ) ‡30 lm (mg L 1) F 0.11 ± 0.03 Biomass of Daphnia NF 0.09 ± 0.04 0.31 0.77 ) galeata (mg L 1) F 0.10 ± 0.05 Copepod biomass NF 0.050 ± 0.005 0.59 0.60 ) (mg L 1) F 0.048 ± 0.003 Crustacean biomass NF 0.14 ± 0.04 0.26 0.81 ) (mg L 1) F 0.15 ± 0.05 Size at maturity of NF 1.28 ± 0.05 1.08 0.34 Daphnia galeata (mm) F 1.33 ± 0.07

experiment, the algae fraction <30 lm was actually week. This value is well within the limiting food dominated by forms <10 lm, accounting for more concentration for D. galeata, below which growth and than 99% of the total cell number of this size class clutch size are reduced (Mu¨ ller-Navarra & Lampert, during the whole experiment. The small size of algae 1996). The significantly larger maximum clutch size in the fraction <30 lm and the low concentration of (7.7 ± 1.5 versus 3.7 ± 0.5; mean ± 1 SD; t-value ¼ 4.2, phytoplankton ‡30 lm may also account for the P ¼ 0.02, d.f. ¼ 3) and the lack of a significant differ- failure of silver carp to gain weight during our ence in maximum body length (1.74 ± 0.14 versus experiment. This explanation is in accordance with 1.80 ± 0.15; t-value ¼ 0.51, P ¼ 0.64, d.f. ¼ 3) in enclo- the observation that cases in which silver carp were sures with and without fish on day 18 of the successfully used for biomanipulation (e.g. Kajak experiment supports this assumption. et al., 1975; Starling, 1993; Datta & Jana, 1998; Similar explanations as for daphnids might hold Starling et al., 1998; Fukushima et al., 1999) are charac- true for the low copepod biomass observed in both terised by phytoplankton communities dominated by treatments. While adult copepods have higher evasive large species or forms [e.g. Microcystis spp., Cylindro- abilities than cladocerans, copepod nauplii are very spermopsis raciborskii (Woloszynska) Seenaya et Subba vulnerable to predation by suction feeders (see review Raju]. Nevertheless, it remains unclear why small in Lazzaro, 1987) such as silver carp (Dong et al., algal species failed to profit from their size refuge in 1992). Accordingly, nauplii biomass has been found to the studies cited above. be negatively affected by silver carp in several studies The decrease of Daphnia biomass in the fish enclo- (e.g. Kajak et al., 1975; Starling & Rocha, 1990; Starling, sures may have been a direct effect of predation by 1993; Domaizon & De´vaux, 1999). Food limitation is silver carp (e.g. Kajak et al., 1975; Opuszynski, 1979; the most reasonable explanation for the decline of Spataru & Gophen, 1985; Domaizon & De´vaux, 1999). copepod biomass in the no-fish enclosures. In general, The decrease in the no-fish enclosures, however, was copepods feed on a particle size spectrum slightly unexpected. The most likely explanation for this larger than that used by daphnids (Sterner, 1989). finding is that food limitation occurred in the no-fish Assuming that only a part of the phytoplankton size enclosures, as indicated by low POC <30 lm levels fraction < 30 lm was available to the adult copepods ) (<0.3 mg L 1) on all sampling dates after the first and taking into consideration that the larger size

2002 Blackwell Science Ltd, Freshwater Biology, 47, 2337–2344 Effects of silver carp 2341

Fig. 1 Dynamics of total phosphorus, Secchi depth, the biomass of phytoplankton <30 and ‡30 lm, particulate organic carbon (POC), Daphnia biomass, copepod biomass and Daphnia size at maturity during an enclosure experiment from 22 June to 16 July 1999. Values are means ± 1 SD of three replicate enclosures with or without silver carp. Significance of treatment effects (fish versus no fish) was analysed with a repeated-measures ANOVA:NS ¼ non-significant; *P < 0.05; **P < 0.01; ***P < 0.001. Total phosphorus values of day 5 of the experiment were identified as outliers and omitted from statistical analysis.

fraction was scarce, it seems most probable that food selective predation (e.g. Pace, Porter & Feig, 1984), by limitation of adult copepods in the no-fish enclosures a phenotypically plastic response to chemical stimuli was even more severe than for D. galeata. exuded by fish (Stibor, 1992), or by indirect effects of The reduction of SAM in Daphnia may be caused by predation (Lampert, 1993). Whereas the first mechan- selection of certain genotypes as a result of size- ism relies on genotypic variability and the presence of

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Table 2 Results of repeated-measures Variable Factor FP ANOVA testing for effects of ﬁsh presence (between) and time (within) from days Secchi depth (m) Fish 51.7 0.002 5–25 of the enclosure experiment. Degrees Time 1.67 0.17 of freedom were 4 and 24 for all variables Fish · time 4.67 0.003 except for total phosphorus (4, 20), where )1 Total phosphorus (lgL ) Fish 0.01 0.93 all values of day 5 of the experiment were Time 2.36 0.08 outliers, and for particulate organic car- Fish · time 0.16 0.97 bon (POC; 3, 18), where one value was ) POC <30 lm (mg L 1) Fish 14.0 0.04 missing on day 15 Time 2.70 0.047 Fish · time 2.32 0.08 ) Biomass of phytoplankton <30 lm (mg L 1) Fish 14.3 0.02 Time 1.51 0.22 Fish · time 1.21 0.34 ) Biomass of phytoplankton ‡30 lm (mg L 1) Fish 0.35 0.58 Time 2.21 0.08 Fish · time 0.94 0.48 ) Biomass of Daphnia galeata (mg L 1) Fish 5.10 0.09 Time 10.4 <0.001 Fish · time 1.43 0.24 ) Copepod biomass (mg L 1) Fish 13.0 0.02 Time 24.9 <0.001 Fish · time 0.24 0.96 ) Crustacean biomass (mg L 1) Fish 7.0 0.06 Time 16.7 <0.001 Fish · time 1.12 0.38 Size at maturity of Daphnia galeata (mm) Fish 167.3 <0.001 Time 6.81 <0.001 Fish · time 5.34 0.001

well-adapted individuals within the population, the selects its prey on the basis of the species and size- second will influence SAM in the next generations specific escape abilities (see review in Lazzaro, 1987; even if no individuals showed the trait before Dong & Li, 1994). Consequently, the reduction of the stimuli became effective. The third factor also SAM observed in our study may have even increased depends on selective predation on large individuals, the vulnerability of daphnids to silver carp predation. which is rather unlikely in the case of a filter-feeding Based on the results of our experiment and earlier fish that selects prey on the basis of prey evasiveness studies, we conclude that the use of silver carp in (Dong & Li, 1994). Results of the present study point biomanipulation is only appropriate if the primary to the second mechanism, a phenotypically plastic aim is to reduce nuisance blooms of large algal species response, because no small-sized individuals repro- (e.g. cyanobacteria), which cannot be effectively con- ducing for the first time were found at the start of the trolled by large herbivorous zooplankton. The com- experiment, nor later in no-fish enclosures, and bined (alternating) use of filter-feeding fish and because D. galeata responded to the presence of fish daphnids as suggested for postwastewater treatment within 1 week after the start of the experiment. This (Smith, 1993) is not feasible in larger lakes, because non-species specific response of Daphnia might be an adequate refuges for the cladocerans are lacking. advantage in the presence of a visually oriented Consequently, stocking of silver carp should be predator (the more common case in temperate lakes) restricted to tropical lakes that are highly productive selecting large individuals, but is a disadvantage if the and naturally lack large cladoceran zooplankton predator is a filter-feeder such as silver carp, which species (Nielssen, 1984).

2002 Blackwell Science Ltd, Freshwater Biology, 47, 2337–2344 Effects of silver carp 2343 Acknowledgments (Aristichthys nobilis Rich.). Journal of Fish Biology, 41, 833–840. We thank G. Egerer for phosphorus analyses and Drenner R.W. & Hambright K.D. (1999) Review: bioma- help in the laboratory, M. Bollenbach for phyto- nipulation of fish assemblages as a lake restoration plankton analysis and F. Wieland for technical technique. Archiv fu¨r Hydrobiologie, 146, 129–165. assistance with the enclosure frame. T. Schulze and Fukushima M., Takamura N., Sun L., Kagawa M., K. Rinke kindly helped in the field. S. Hu¨ lsmann, M. Matsushige K. & Xie P. (1999) Changes in the plankton Gessner and two anonymous referees gave helpful community following introduction of filter-feeding comments on the manuscript. This study was sup- planktivorous fish. Freshwater Biology, 42, 719–735. ported by Landestalsperrenverwaltung Sachsen and Gliwicz Z.M. & Pijanowska J. (1989) The role of predation Arbeitsgemeinschaft Trinkwassertalsperren e.V. in zooplankton succession. In: Plankton Ecology: Succes- sion in Plankton Communities (Ed. U. Sommer), pp. 253– (ATT). 296. Springer-Verlag, Berlin. Herodek S., Ta´trai I., Olah J. & Vo¨ro¨s L. (1989) Feeding References experiments with silver carp (Hypophthalmichthys molitrix Val.) fry. Aquaculture, 83, 331–344. Arbeitsgemeinschaft Trinkwasser e.V. Arbeitskreis Biol- Horn W. & Horn H. (1995) Interrelationships between ogie (Ed.) (1998) Erfassung und Bewertung von Plankton- crustacean zooplankton and phytoplankton: results organismen. ATT-Technische Informationen Nr. 7. from 15 years of field observations at the mesotrophic Oldenbourg Verlag, Mu¨ nchen. Saidenbach Reservoir (Germany). Hydrobiologia, 307, Benndorf J. (1995) Possibilities and limits for controlling 231–238. eutrophication by biomanipulation. Internationale Revue Horn W., Horn H. & Paul L. (1994) Long-term trends in der Gesamten Hydrobiologie, 80, 519–534. the nutrient input and in-lake concentrations of a Bottrell H.H., Duncan A., Gliwicz Z.M., Grygierek E., drinking water reservoir in a dense populated catch- Herzig A., Hilbricht-Ilkowska A., Kurasawa H., Lars- ment area (Erzgebirge, Germany). Internationale Revue son P. & Weglenska T. (1976) A review of some der Gesamten Hydrobiologie, 79, 213–227. problems in zooplankton production studies. Norwe- Horn H., Paul L. & Horn W. (2001) Phytoplanktonzu- gian Journal of Zoology, 24, 419–456. nahme trotz fallender P-Belastung – ein Widerspruch? Burns C.W. (1968) The relationship between body size of Ursachen der unerwarteten Entwicklung in einer filter-feeding cladocera and the maximum size of Trinkwassertalsperre. Gwf Wasser Abwasser, 142, 268– particles ingested. Limnology and Oceanography, 13, 278. 675–678. Institut fu¨ r Wasserwirtschaft Berlin (Ed.) (1986) Aus- Costa-Pierce B.A. (1992) Review of the spawning re- gewa¨hlte Methoden der Wasseruntersuchung. Gustav quirements and feeding ecology of silver carp (Hyp- Fischer, Jena. ophthalmichthys molitrix) and reevaluation of its use in Kajak Z., Rybak J.I., Spodniewska I. & Godlewska- fisheries and aquaculture. Reviews in Aquatic Sciences, 6, Lipowa W.A. (1975) Influence of the planktonivorous 257–273. fish Hypophthalmichthys molitrix (Val.) on the plankton Datta S. & Jana B.B. (1998) Control of bloom in a tropical and benthos of the eutrophic lake. Polskie Archivum lake: grazing efficiency of some herbivorous fishes. Hydrobiologii, 22, 301–310. Journal of Fish Biology, 53, 12–24. Lampert W. (1993) Phenotypic plasticity of the size at Domaizon I. & De´vaux J. (1999) Impact of moderate first reproduction in Daphnia: the importance of silver carp biomass gradient on zooplankton com- maternal size. Ecology, 74, 1455–1466. munities in a eutrophic reservoir. Consequences for Lazzaro X. (1987) A review of planktivorous fishes: the use of silver carp in biomanipulation. Comptes their evolution, feeding behaviours, selectivities, and Rendus de l’Acade´mie des Sciences Paris, Life Sciences, 322, impacts. Hydrobiologia, 146, 97–167. 621–628. Lieberman D.M. (1996) Use of silver carp (Hypophthal- Dong S. & Li D. (1994) Comparative studies on the michthys molitrix) and bighead carp (Aristichthys nobilis) feeding selectivity of silver carp Hypophthalmichthys for algae control in a small pond: changes in water molitrix and bighead carp Aristichthys nobilis. Journal of quality. Journal of Freshwater Ecology, 11, 391–397. Fish Biology, 44, 621–626. Miura T. (1990) The effects of planktivorous fishes on the Dong S., Li D., Bing X., Shi Q. & Wang F. (1992) Suction plankton community in a eutrophic lake. Hydrobiologia, Volume and filtering efficiency of silver carp 200 ⁄ 201, 567–579. (Hypophthalmichthys molitrix Val.) and bighead carp

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