Article

Stocking of herbivorous fish in eutrophic shallow clear-water lakes to reduce standing height of submerged macrophytes while maintaining their biomass

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Abstract

To balance the conservation value versus recreational use of shallow lakes, moderate herbivory may be needed in eutrophic lakes to avoid near surface growth while maintaining high vegetation biomass close to the sediment. However, over-grazing or even complete elimination of macrophytes by grass carp (Ctenopharyngodon idella) commonly used for control purposes has often been observed, leading to a shift from a clear to a turbid phy-toplankton-dominated state. We hypothesized that slow-growing and smaller-sized herbivorous fish species might be more suitable than grass carp to obtain the desired moderate control because they consume the top part of the vegetation without severely affecting the lower plant parts. To test the hypothesis, the effects of Wuchang bream (Megalobrama amblycephala), an endemic medium-sized herbivorous cyprinid, and grass carp on the biomass, density and trait of the macrophyte Vallisneria denseserrulata were compared in an enclosure experiment. We found that V. denseserrulata grew less tall but did not lose biomass under moderate herbivory by Wuchang bream due to increased plant density and leaf weight per length, whereas excessive herbivory by grass carp had strong negative effects on the plant biomass. Moreover, the plant had more and thicker leaves in the fish treatments than in the fishless controls. The growth of grass carp was much faster than that of Wuchang bream. Our findings suggest that stocking of Wuchang bream in proper densities may be more useful than grass carp for the management of V. denseserrulata and likely also other macrophyte species. More tests, especially at different fish densities are, however, needed to draw any firm conclusions regarding this hypothesis.

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... After collection, SAV was thoroughly cleaned to remove invertebrates and sediments, and then dried at 80 • C for 3 days to determine dry weight (g). Plant height in the water column was determined with a ruler (to the nearest 1 mm), and the total percent coverage of SAV was measured using the hand-drawing method in six randomly positioned 1 m 2 sample squares (Zhen et al., 2018). ...
... Herbivorous fish affect the growth of SAV through grazing directly (Nurminen et al., 2003). Numerous studies have demonstrated that excessive stocking of herbivorous fish precipitates SAV loss (Hanlon et al., 2000;Dibble and Kovalenko, 2009;Zhen et al., 2018). In addition to supplying water, shallow subtropical lakes within the MLYRB support important fisheries, and both benthivorous fish (principally common carp and crucian carp) and herbivorous fish (principally grass carp and bream) are stocked extensively (Chen et al., 1989;Li et al., 2010). ...
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Fish community manipulation and regulation has been largely overlooked as a mitigation strategy for restoring submerged aquatic vegetation (SAV) in shallow lakes of the middle and lower Yangtze River Basin (MLYRB). An in-situ fish exclusion experiment and a large-scale lake manipulation were conducted to test the hypothesis that the reasonable removal of benthivorous and herbivorous fish would facilitate the restoration and reconstruction of SAV in shallow lakes within the MLYRB. The in-situ exclusion experiment was conducted from April to October in 2017. Electrofishing was used to remove benthivorous and herbivorous fish from the exclosures. SAV were then artificially planted in the same pattern and density in both exclosures and adjacent open sites, and responses were measured for seven consecutive months. The mean percent coverage and biomass of SAV in the exclosures increased quickly and remained significantly higher than those in open sites over the duration of the experiment. Water quality also improved as turbidity, chlorophyll-a, total phosphorus and total nitrogen in the exclosures remained significantly lower than those in the open sites. After the in-situ experiment, a larger scale manipulation of fish in the entire submerged macrophyte zone (SMZ) was implemented from 2017 to 2020. After removing more than 2/3 of the benthivorous and herbivorous fish biomass by October 2020 in the SMZ, both the species richness and spatial coverage of SAV increased from 2 to 9 and from 1.7% to 32.2%, respectively. Our results provided clear evidence that fish are strong regulators of SAV productivity and that their reasonable removal facilitates ecological recovery. Therefore, we propose that fish community manipulation as implemented in this study be given more attention in addition to the reduction of external nutrient loading when designing projects to restore SAV in shallow lakes of the MLYRB.
... They assimilate the nutrients from submerged macrophytes or convert them into feces. Besides their consumptive role, some positive effects of herbivores on submerged macrophytes have been observed, such as promoting over-compensatory growth and halting the regime shift in shallow lakes from clear to turbid after the restoration of submerged macrophytes [7,8]. However, the effect of herbivorous fish activities on the overall nutrient dynamics between overlying water and sediment during the restoration process has received limited attention. ...
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Submerged macrophytes are essential for the restoration of shallow lakes for maintaining clear-water conditions. The presence of fish can affect the nutrient cycles and the growth of submerged macrophytes in lakes. In this study, a 28-day mesocosm experiment was carried out with an herbivorous fish Ctenopharyngodon idella (CID) and an omni-benthivorous fish Carassius auratus (CAU) to investigate their effects on the growth of a submerged macrophyte Hydrilla verticillata and phosphorus (P) cycle in shallow lakes. The results showed that CID slowed down the growth of H. verticillata while CAU showed no significant effect. In overlying water, CID only increased the ammonium nitrogen (NH3-N) concentration in the later stage due to excretion, while CAU elevated particulate phosphorus (PP) levels during the experiment through disturbance. Meanwhile, the radial oxygen loss and photosynthesis of H. verticillata in CAU might promote the formation of NaOH-P and HCl-P in the sediment, respectively. Changes in the water and sediment properties caused by CID and CAU can contribute to the increase in the eutrophication risk index (ERI). Our findings suggest that CID has the potential to be an indirect biological manipulation tool, while CAU should be controlled to minimize its negative impacts on the P cycle in lakes.
... stipulacea is a native species growing in the same niche as the invasive species, it might be a better candidate for littoral zone restoration. Our study also showed that V. denseserrulata had a strong ability to expand horizontally due to its large ramet number and relatively small plant height, and it therefore seems to be a good candidate for lake restoration, as also stated elsewhere [46]. Another submerged species, P. lucens, with abundant ramets and larger height, could be used in specific restoration projects that allow the macrophytes to reach the water surface. ...
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Aquatic plants play a key role in the structuring and functioning of shallow lake ecosystems. However, eutrophication often triggers shifts in plant communities and species diversity, especially in the early stages when the water is still clear. Additionally, water depth is an important factor regulating aquatic plant communities. We conducted a 50-day mesocosm study to investigate how water depth (50 cm and 100 cm) affected the functional traits (vertical expansion versus horizontal colonisation) of 20 aquatic plants under eutrophic clear-water conditions. Among the selected species, the submerged plants Hydrocotyle vulgaris and Limnophila indica exhibited higher plant height or biomass in deeper water, while the emergent plants Myriophyllum aquaticum showed the opposite trend. Additionally, Ludwigia peploides subsp. stipulacea exhibited better vertical growth than the remaining species, and the submerged species Vallisneria denseserrulata had better horizontal colonisation. There was a positive correlation between plant height and rhizome length, indicating the absence of a trade-off between vertical growth and horizontal expansion. Our findings suggest an overall resilience of aquatic plants to varying water depths within our study range and highlight the importance of analysing functional traits when selecting appropriate species in freshwater ecosystem restoration, particularly in the face of climate change-induced water depth fluctuations.
... It underpins that the macrophytes might be seen as an ecological habitat entity for building up their own network for connecting food and energy exchange (see also Zhang et al., 2016;Wolters et al., 2019). Another important role of macrophyte habitat architecture for aquatic ecosystems is seen in the provisioning of food and shelter for spawning and nursery of vertebrates as discussed for fish in different studies (Petr, 2000;Meulenbroek et al., 2018;Figueiredo et al., 2013;Yofukuji et al., 2021; macrophytes themself can be a significant food source for fish: Yu et al., 2016;Löffler, 1988;Zhen et al., 2018). Also for Alte Donau, Waidbacher and Drexler (2018) verified macrophytes and phytal biota as important food sources and macrophyte stands as valued niches for young fish. ...
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... Alternatively, an unbalanced fish community can have a negative impact on water quality and lake ecosystem function (Cai, 2017;Guo et al., 2022). For example, the overabundance of herbivorous fish can precipitate submerged macrophyte loss in shallow lakes through over-grazing (Zhen et al., 2018). Often affected by overfishing and habitat loss, piscivorous fish in most MLYRB lakes and rivers have dramatically declined over the past decades, which has led to the proliferation of small-bodied fishes (Mao et al., 2011;Cai et al., 2019). ...
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With the intensification of eutrophication, many artificial water supply lakes that act as a biological filter for water diverted from rivers have been built to alleviate water scarcity in Eastern China. In this study, we selected Lake Yanlong, a representative artificial water supply lake in Yancheng City, as our experimental lake to explore how the community composition of fishes changed among different habitat types and assess potential consequences for effective water treatment. From October 2015 to October 2020, we conducted quarterly surveys of fish communities and environmental factors in the Mangshe River (MR; water for lake) compared to four different water treatment zones of Lake Yanlong (PZ, the pretreatment zone with inlet from the MR; EZ, the emergent macrophyte zone; SZ, the submerged macrophyte zone; DZ, the deep purification zone with outlet to urban waterworks). A total of 16,339 individual fish belonging to 11 families and 49 species were collected. Six of the eight dominant species observed across zones were small-bodied fishes. Despite reduced fish species richness, the relative abundance and biomass of fishes tended to be higher in Lake Yanlong relative to the MR. The Shannon-Wiener diversity index, Pielou evenness index, Simpson’s diversity index all decreased from the MR to the DZ in the following sequence: MR < PZ < EZ < SZ < DZ. Analysis of similarities and similarity percentage analysis confirmed that fish communities differed significantly among zones and Coilia ectenes, Carassius auratus, Pseudobrama simony, Hemiculter leucisculus, and Hemiculter bleekeri were the major differentiating species. Mantel’s test and redundancy analysis revealed that water depth, aquatic vegetation coverage, and phytoplankton concentrations were the major factors determining the spatial distribution of fishes when moving from the MR to the DZ of Lake Yanlong. Stocking piscivorous fish can be used as an effective measure to control the abundance of prolific small-bodied fishes in Lake Yanlong. The details backing these findings are important for understanding how the community composition of fishes among habitat types in Lake Yanlong influence water quality, and to develop suitable biomanipulation strategies for the management of fish resources and maintaining proper function of these artificial water supply lakes.
... A study by Zhen et al. (2018) suggested that M. amblycephala grazing on H. verticillata consume greater biomass than conspecifics grazing on V. denseserrulata. The same study demonstrated that while V. denseserrulata is grazed by M. amblycephala, the impact is limited to the extent that total biomass of V. denseserrulata in a system can still increase. ...
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... The reason for the similar plant heights may be mainly attributable to the shallow water depth in the cement ponds during the experiment (always maintained at 150 cm), which limited the space for plant growth. http Changes in the fish community structure will inevitably affect other aquatic communities and the structure and function of the entire lake ecosystem (Gu et al., 2018;Zhen et al., 2018). A previous study on some temperate lakes has shown that the ultimate cause for the transition from a macrophyte-dominated state to a phytoplanktondominated state is changes in the fish community structure (Brönmark and Weisner, 1992). ...
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Plants are attacked by many different consumers. A critical question is how often, and under what conditions, common reductions in growth, fecundity or even survival that occur due to herbivory translate to meaningful impacts on abundance, distribution or dynamics of plant populations. Here, we review population-level studies of the effects of consumers on plant dynamics and evaluate: (i) whether particular consumers have predictably more or less influence on plant abundance, (ii) whether particular plant life-history types are predictably more vulnerable to herbivory at the population level, (iii) whether the strength of plant-consumer interactions shifts predictably across environmental gradients and (iv) the role of consumers in influencing plant distributional limits. Existing studies demonstrate numerous examples of consumers limiting local plant abundance and distribution. We found larger effects of consumers on grassland than woodland forbs, stronger effects of herbivory in areas with high versus low disturbance, but no systematic or unambiguous differences in the impact of consumers based on plant life-history or herbivore feeding mode. However, our ability to evaluate these and other patterns is limited by the small (but growing) number of studies in this area. As an impetus for further study, we review strengths and challenges of population-level studies, such as interpreting net impacts of consumers in the presence of density dependence and seed bank dynamics.
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One of the most serious problems caused by eutrophication of shallow lakes is the disappearance of submerged macrophytes and the switch to a turbid, phytoplankton-dominated state. The reduction of external nutrient loads often does not result in a change back to the macrophyte-dominated state because stabilising mechanisms that cause resilience may delay a response. Additional internal lake restoration measures may therefore be needed to decrease the concentration of total phosphorus and increase water clarity. The re-establishment of submerged macrophytes required for a long-term stability of clear water conditions, however, may still fail, or mass developments of tall-growing species may cause nuisance for recreational use. Both cases are often not taken into account when restoration measures are planned in Germany, and existing schemes to reduce eutrophication consider the topic inadequately. Here we develop a step-by-step guideline to assess the chances of submerged macrophyte re-establishment in shallow lakes. We reviewed and rated the existing literature and case studies with special regard on (1) the impact of different internal lake restoration methods on the development of submerged macrophytes, (2) methods for the assessment of natural re-establishment, (3) requirements and methods for artificial support of submerged macrophyte development and (4) management options of macrophyte species diversity and abundance in Germany. This guideline is intended to help lake managers aiming to restore shallow lakes in Germany to critically asses and predict the potential development of submerged vegetation, taking into account the complex factors and interrelations that determine their occurrence, abundance and diversity.
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We investigated effects of triploid grass carp Ctenopharyngodon idella on aquatic macrophyte communities, water quality, and public satisfaction for 98 lakes and ponds in Washington State stocked with grass carp between 1990 and 1995. Grass carp had few noticeable effects on macrophyte communities until 19 months following stocking. After 19 months, submersed macrophytes were either completely eradicated (39% of the lakes) or not controlled (42% of the lakes) in most lakes. Intermediate control of submersed macrophytes occurred in 18% of lakes at a median stocking rate of 24 fish per vegetated surface acre. Most of the landowners interviewed (83%) were satisfied with the results of introducing grass carp. For sites where all submersed macrophytes were eradicated, average turbidity was higher (11 nephelometric turbidity units, NTU) than at sites where macrophytes were controlled to intermediate levels (4 NTU) or unaffected by grass carp grazing (5 NTU). Chlorophyll a was not significantly different between levels of macrophyte control; therefore, we concluded that most of this turbidity was abiotic and not algal. Triploid grass carp were a popular control option and effectively grazed most submersed macrophytes in Washington State. However, calculating stocking rates based on landowner estimates of aquatic plant coverage rarely resulted in intermediate levels of aquatic plant control. Additionally, the effects of particular stocking rates varied considerably. We recommend against using grass carp in Washington lakes where eradication of submersed vegetation cannot be tolerated.
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The state of knowledge of grass carp ( Ctenopharyngodon idella Val.) effects on water bodies are summarized based on a review of selected literature and my own experience from South Bohemian ponds. The subjects considered include aquatic plant control using grass carp, fish age and stocking densities, and direct and indirect consequences of its intro- duction to water bodies including impacts on water and sedi- ment chemistry, phytoplankton, zooplankton, zoobenthos, fish, amphibian and water birds communities. Lastly, longevi- ty of plant control by the grass carp is addressed. An attempt has also been made to identify weaknesses in the available in- formation.
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Fish have a major structuring impact on the Zooplankton communities in lakes (Hrbacek et al., 1961; Brooks and Dodson, 1965) that may cascade to the lower trophic levels and chemical environment (Carpenter et al., 1985; Carpenter and Kitchell, 1993). Ample evidence is available from enclosure experiments (e.g., Christoffersen et al., 1993), whole-lake experiments (e.g., Shapiro et al., 1975; Benndorf, 1987; Gulati et al., 1990; Carpenter and Kitchell, 1993), and empirical analyses (Jeppesen et al., 1990, 1997). More recently, it has become evident that 0+ fish may play a key role in Zooplankton population dynamics (Cryer et al., 1986; Mills et al., 1987), and some studies suggest that fish larvae are responsible for the midsummer decline in Zooplankton (Luecke et al., 1990; Jeppesen et al., 1997), a phenomenon that is often attributed to increased density of inedible phytoplankton such as cyanobacteria (e.g., De Bernardi and Guisanni, 1990). Whole-lake (Søndergaard et al., 1997) and enclosure (He and Wright, 1992) experiments support the structuring role of 0+ fish. How the importance of top-down control of Zooplankton by fish varies along a trophic gradient is debated extensively. McQueen et al. (1986) suggested that the cascading effect of zooplank-tivorous fish is stronger in oligotrophic lakes than in eutrophic lakes, but a growing body of literature argues that the cascading effect of fish is greater in eutrophic and hypertrophic lakes with respect to the food web in the classic sense
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This study evaluated longevity and population persistence of 768,500 triploid grass carp (Ctenopharyngodon idella Valen- ciennes) stocked in the 70,000-ha Santee Cooper system in South Carolina from 1989 through 1996 to control hydrilla (Hydrilla verticillata (L.f.) Royle). Collected from 1998 through 2002, the oldest of 477 fish were age 11. Total annu- al mortality rates ranged from 22% to 39% meaning 10% of a cohort could persist for 5 to 9 years. Longevity and persis- tence measured in this study demonstrate that benefits of aquatic plant control and risks to non-target organisms need to be carefully balanced. Annual stocking of as many as 150,000 could potentially leave numerous fish in this system for almost a decade. Conversely, control of hydrilla, achieved
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Studies of the plant contribution to the food of fish in eutrophic lakes in Poland show that roach (Rutilus rutilus) and rudd (Scardinius erythrophthalmus), which frequently dominate in biomass and numbers, are the main plant consumers. Submerged macrophytes and filamentous algae are the most important plant food. The fish examined feed selectively on macrophytes and show a preference for species with low cost/ benefit ratio. The variability of plant ingestion according to temperature and the size of fish is discussed, and estimates of the annual consumption of algae and macrophytes by fish in the lakes examined are given. The possibility and effectiveness of mechanical and enzymatic processing of the ingested plants are presented. Qualitative and quantitative descriptions of faeces as well as their possible impact on the lake system are given. The herbivorous fish studied were found to be relatively efficient grazers but inefficient assimilators, thus they play a significant role in initiating the internal, biologically mobilized, nutrient sources.
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The sea urchin, Lytechinus variegatus, has been estimated to consume between 50 and 90% of annual net aboveground production in selected turtlegrass (Thalassia testudinum) meadows in the eastern Gulf of Mexico. Nevertheless, turtlegrass persists where sea urchin grazing is intense. We hypothesized that turtlegrass productivity is stimulated by grazing, as has been reported from terrestrial grassland systems, and that this best explains the persistence of heavily grazed turtlegrass in St. Joseph Bay, Fla. This hypothesis was tested by manipulating sea urchin densities (0, 10, and 20 individuals/m2) in 1-m2 enclosures. These densities encompass the range of average densities at the study site and those reported in the literature. Changes in turtlegrass abundance (e.g., short shoot density and biomass), production by short shoots, and leaf width were monitored in these enclosures during the summer. Repeated-measures ANOVA showed that production by short shoots, leaf density/shoot, and leaf width decreased over time in all treatments. Leaf density/shoot and leaf width were not significantly impacted by grazing, nor did grazing significantly reduce seagrass biomass, but it did lead to significantly higher densities of short shoots than found in control cages. Our results indicate that turtlegrass compensates for the effects of sea urchin herbivory by increasing the recruitment of short shoots during the growing season. We estimate that this increased shoot density led to a 40% increase in net aboveground primary production (g dry weight/m2) in grazing treatments, which helps to explain the lack of significant reductions of sea grass biomass during the growing season.
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Grass carp (Ctenopharyngodon idella) were collected from Lake Wales, Florida, a hydrilla (Hydrilla verticillata) infested lake, for a 4-year period. Average daily growth per year ranged from 10.0 to 10.4 g/day. Grass carp averaged 962 mm total length and 15.0 kg after 48 months.
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The turbidity of lakes is generally considered to be a smooth function of their nutrient status. However, recent results suggest that over a range of nutrient concentrations, shallow lakes can have two alternative equilibria: a clear state dominated by aquatic vegetation, and a turbid state characterized by high algal biomass. This bi-stability has important implications for the possibilities of restoring eutrophied shallow lakes. Nutrient reduction alone may have little impact on water clarity, but an ecosystem disturbance like foodweb manipulation can bring the lake back to a stable clear state. We discuss the reasons why alternative equilibria are theoretically expected in shallow lakes, review evidence from the field and evaluate recent applications of this insight in lake management.
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Lake water eutrophication has become one of the most important factors impeding sustainable economic development in China. Knowledge of the current status of lake water eutrophication and determination of its mechanism are prerequisites to devising a sound solution to the problem. Based on reviewing the literature, this paper elaborates on the evolutional process and current state of shallow inland lake water eutrophication in China. The mechanism of lake water eutrophication is explored from nutrient sources. In light of the identified mechanism strategies are proposed to control and tackle lake water eutrophication. This review reveals that water eutrophication in most lakes was initiated in the 1980s when the national economy underwent rapid development. At present, the problem of water eutrophication is still serious, with frequent occurrence of damaging algal blooms, which have disrupted the normal supply of drinking water in shore cities. Each destructive bloom caused a direct economic loss valued at billions of yuan. Nonpoint pollution sources, namely, waste discharge from agricultural fields and nutrients released from floor deposits, are identified as the two major sources of nitrogen and phosphorus. Therefore, all control and rehabilitation measures of lake water eutrophication should target these nutrient sources. Biological measures are recommended to rehabilitate eutrophied lake waters and restore the lake ecosystem in order to bring the problem under control.
Article
One of the most serious problems caused by eutrophication of shallow lakes is the disappearance of submerged macrophytes and the switch to a turbid, phytoplankton-dominated state. The reduction of external nutrient loads often does not result in a change back to the macrophyte-dominated state because stabilising mechanisms that cause resilience may delay a response. Additional internal lake restoration measures may therefore be needed to decrease the concentration of total phosphorus and increase water clarity. The re-establishment of submerged macrophytes required for a long-term stability of clear water conditions, however, may still fail, or mass developments of tallgrowing species may cause nuisance for recreational use. Both cases are often not taken into account when restoration measures are planned in Germany, and existing schemes to reduce eutrophication consider the topic inadequately. Here we develop a step-by-step guideline to assess the chances of submerged macrophyte re-establishment in shallow lakes. We reviewed and rated the existing literature and case studies with special regard on (1) the impact of different internal lake restoration methods on the development of submerged macrophytes, (2) methods for the assessment of natural re-establishment, (3) requirements and methods for artificial support of submerged macrophyte development and (4) management options of macrophyte species diversity and abundance in Germany. This guideline is intended to help lake managers aiming to restore shallow lakes in Germany to critically asses and predict the potential development of submerged vegetation, taking into account the complex factors and interrelations that determine their occurrence, abundance and diversity.
A biological study of Megalobrama amblycephala and Megalobrama terminalis of Lake Liangzi
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Cao, W., 1960. A biological study of Megalobrama amblycephala and Megalobrama terminalis of Lake Liangzi. Acta Hydrobiologica Sinica. 1, 57-82 (in Chinese).
Problems and prospects for grass carp as a management tool
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Cassani, J.R., 1995. Problems and prospects for grass carp as a management tool. Am. Fish. Soc. Sympo. 15, 407-412.
Histological study of the digestive tract of grass carp
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Ni, D., Hong, X., 1963. Histological study of the digestive tract of grass carp. Acta Hydrobiologica Sinica 3, 1-25 (in Chinese).
The Cyprinid Fishes in China
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Wu, X., Cao, W., Yi, B., Yang, G., Luo, Y., 1964. The Cyprinid Fishes in China. Shanghai Science and Technology Press, Shanghai (in Chinese).