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Ecological Impact of Grass Carp: A Review of the Available Data

January 2009
Journal of Aquatic Plant Management 47(1)

Authors:

University of Minnesota Duluth

The exotic grass carp ( Ctenopharyngodon idella ) has been used for almost a half a century in the United States as a bi- ological agent to control and manage aquatic plants. This long-lived generalist herbivore consumes large amounts of vegetation and can considerably alter habitat and impact aquatic communities. We conducted a literature review to determine whether previous studies adequately addressed ecological impacts of grass carp and their underlying mech- anisms. Our goal was to identify strengths and limitations of ecological assessment in the literature and suggest a trajec- tory of future research. The review yielded 1,924 citations on grass carp; however, data on ecological interactions were limited, and most research emphasized the biology of grass carp or eradication of aquatic plants rather than ecological mechanisms responsible for ecosystem-wide impacts. Very few studies addressed effects on habitat complexity or com- munity-structuring processes. We provide a comprehensive tabulated overview of feeding preferences and environmen- tal impacts of grass carp. We argue that ecology is para- mount to evaluating grass carp impacts and thorough understanding of these impacts is essential for the appro- priate management of aquatic communities. Current knowledge is not sufficient to accurately predict long-term effects of grass carp on freshwater ecosystems. We advise a more cautious approach to developing guidelines for grass

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J. Aquat. Plant Manage.

47: 2009. 1

J. Aquat. Plant Manage.

47: 1-15

Ecological Impact of Grass Carp:

A Review of the Available Data

ERIC D. DIBBLE AND KATYA KOVALENKO

ABSTRACT

The exotic grass carp (

Ctenopharyngodon idella

) has been

used for almost a half a century in the United States as a bi-

ological agent to control and manage aquatic plants. This

long-lived generalist herbivore consumes large amounts of

vegetation and can considerably alter habitat and impact

aquatic communities. We conducted a literature review to

determine whether previous studies adequately addressed

ecological impacts of grass carp and their underlying mech-

anisms. Our goal was to identify strengths and limitations of

ecological assessment in the literature and suggest a trajec-

tory of future research. The review yielded 1,924 citations

on grass carp; however, data on ecological interactions were

limited, and most research emphasized the biology of grass

carp or eradication of aquatic plants rather than ecological

mechanisms responsible for ecosystem-wide impacts. Very

few studies addressed effects on habitat complexity or com-

munity-structuring processes. We provide a comprehensive

tabulated overview of feeding preferences and environmen-

tal impacts of grass carp. We argue that ecology is para-

mount to evaluating grass carp impacts and thorough

understanding of these impacts is essential for the appro-

priate management of aquatic communities. Current

knowledge is not sufﬁcient to accurately predict long-term

effects of grass carp on freshwater ecosystems. We advise a

more cautious approach to developing guidelines for grass

carp use.

Key words:

aquatic plant management,

Ctenopharyngodon

idella

, habitat alteration, literature review.

INTRODUCTION

During the last 45 years, a considerable amount of infor-

mation has been published on grass carp,

Ctenopharyngodon

idella

(Val.). Reports of grass carp use in management started

to proliferate in the mid 1970s, approximately 10 years after

the ﬁrst grass carp were stocked into Arkansas reservoirs with

the hope that this large exotic herbivore would control

growth of noxious aquatic plants (Pierce 1983). These ﬁrst

reports emphasized the biology and physiology of the ﬁsh

and its feasibility as a tool for weed control (Sills 1970, Stott

and Robson 1970, Shireman and Maceina 1981, Shireman

1984, Wiley et al. 1984, 1987, Leslie et al. 1987). Much of this

literature was stimulated by the apparent success and efﬁ-

ciency grass carp demonstrated in reducing and even eradi-

cating entire macrophyte communities. Encouraged by the

enthusiasm of ﬁnding an effective management tool for an

ever-increasing problem of invasive plant infestations, this

emphasis prevailed in the literature for more than a decade.

By the mid-to-late 1980s, the interest shifted toward address-

ing questions of the direct impacts these herbivores had on

environmental parameters other than targeted aquatic

plants.

Concurrently, literature was developing in the disci-

pline of aquatic ecology that addressed indirect effects on

the structuring of aquatic communities. Much of this liter-

ature emphasized effects of exotic introductions and dom-

inant organisms on community structure (Pimm 1987,

Ross 1991, Simberloff 1990, Soule 1990, Vitousek 1990)

and provided evidence that a keystone species can alter

environmental conditions and mediate community pro-

cesses (Paine 1966), along with other indirect mechanisms

responsible for altering community structure (Kerfoot

and Sih 1987). Many of these mechanisms involve multi-

species interactions, such as competition, predator-prey

interactions, and aquatic plants as ecologically important

components within aquatic ecosystems (Jeppesen et al.

1997). Submerged macrophytes are important for water

quality, nutrient dynamics, and invertebrate-ﬁsh interac-

tions (Jeppesen et al. 1997 and references therein). Spa-

tial heterogeneity across a landscape is important for

ecological interactions (Palmer and Poff 1997, Schaffer

1981). Like a landscape, a waterscape exhibits similar het-

erogeneity due to the differences in spatial complexity

and structural habitat provided by aquatic plants. Habitat

heterogeneity in aquatic systems mediates mechanisms re-

sponsible for determining trophic interactions, animal

distribution (Werner and Hall 1979, Savino and Stein

1982, Mittelbach 1988, Diehl 1993), and community com-

position, such as species diversity and abundance (Gilin-

sky 1984, Adams and DeAngelis 1987). It was previously

thought that macrophytes provide few functions other

than physical structure, but now it is clear they are grazed

by a variety of animals (Lodge et al. 1997) and also indi-

rectly contribute to lake primary productivity by support-

ing large biomass of periphyton (Wetzel 2001). Vegetated

habitats provide abundant food reserves for mammals, wa-

terfowl, amphibians, reptiles, ﬁsh, and invertebrates

(Swanson and Meyer 1973, Pardue and Nielsen 1979, Gi-

linsky 1984, Keast 1984, Eldridge 1990, Fredrickson and

Laubhan 1996). Grass carp can cause major reduction or

complete elimination of aquatic plants when introduced

into aquatic systems (Van Dyke et al. 1984, Wiley et al.

1987, Klussman et al. 1988). Diversity of aquatic plant

communities can be reduced considerably, even at carp

Department of Wildlife and Fisheries, P.O. Box 9690, Mississippi State

Univ., Mississippi State, MS 39762. Received for publication September 2,

2007 and in revised form September 9, 2008.

J. Aquat. Plant Manage.

47: 2009.

densities typically required to control a target plant spe-

cies (Stott and Robson 1970, Stott 1977, Fowler and Rob-

son 1978, Shireman and Maceina 1981). Because such

changes in a plant community signiﬁcantly alter the habi-

tat and interactions of many aquatic organisms, it is pru-

dent to ﬁrst develop a thorough understanding of how an

exotic herbivorous ﬁsh can inﬂuence the aquatic commu-

nity before assessing its feasibility as a management tool.

Previous reviews have discussed mostly biology and feed-

ing preferences of grass carp, management applications such

as stocking rates, and effects on water quality (e.g., Bain

1993, Petr 2000, Cudmore and Mandrak 2004, Pipalova

2006). None of the previous reviews, however, emphasized

ecological interactions or attempted to address potential

mechanisms responsible for grass carp impacts. The goals of

this review are to evaluate the availability of data in previous

research on grass carp that attempt to validate community

impacts, identify strengths and limitations of this research,

and determine potential design and trajectory of future re-

search, and protocol for use of grass carp as a biocontrol

agent.

We used mainly BIOSIS previews and Cambridge Scientif-

ic Abstracts to search the literature and yielded 1,924 undu-

plicated citations on grass carp, 166 of which were pertinent

to this review. Research topics and the type of response vari-

ables quantiﬁed in the research were summarized, and rela-

tive prevalence of each topic was determined by calculating

the frequency of its occurrence. Publications were evaluated

on the basis of whether they attempted to: (1) quantify im-

pacts on community structure and process; (2) measure re-

sponse variables at habitat, population and/or individual

levels; and (3) investigate direct and indirect impacts on the

aquatic community. A direct impact was deﬁned as a single-

level interaction such as immediate alteration of plant abun-

dance due to grass carp feeding activities; indirect impacts

were deﬁned as multi-level interactions, such as changes in

zooplankton composition as a result of the increase in phy-

toplankton abundance due to accelerated nutrient loading

facilitated by grass carp foraging activities (Miller and Ker-

foot 1987).

RESULTS AND DISCUSSION

Our review of the literature suggested that data are limit-

ed for a thorough assessment of grass carp impacts on the

aquatic community. We found that most research is related

to the eradication of aquatic plants rather than ecological

mechanisms potentially responsible for the impacts. Limited

data are available to validate long-term consequences and in-

direct impacts of system-wide introductions of grass carp.

Fewer than 50 citations addressing grass carp impacts re-

ferred to the term “ecology,” and of these, only a few (<10)

inferred ecological processes, yet did not validate causal

mechanisms (Table 1). The two most common response vari-

ables measured in studies investigating potential impacts by

the carp on aquatic communities were direct impact on

aquatic plants and indirect alteration of water quality. Less

than 2% of all studies investigated structural alteration of

habitat or the dynamic processes responsible for structuring

the aquatic community.

Direct impacts

Aquatic plant abundance

Changes in plant abundance and community composition

occur due to immediate foraging activities as well as alter-

ation of water transparency, disturbance of the sediment,

and deposition of fecal matter by grass carp. Grass carp intro-

ductions may lead to unexpected and undesirable changes

in the plant community. Hanlon et al. (2000) reported sever-

al cases of hydrilla (

Hydrilla verticillata

[L.f.] Royle) over-

growth after carp introduction. A shift in plant community

composition to less palatable/grazing-resistant species has al-

so been observed (Vinogradov and Zolotova 1974, Hanlon et

al. 2000, Pipalova 2002). Several studies reported that grass

carp eliminated native plants, leaving invasive vegetation in-

tact (Van Dyke 1994, McKnight and Hepp 1995). Limited da-

ta are available to quantify the direct impact on non-target

plants since many studies focused only on speciﬁc plant spe-

cies targeted for control and did not assess other plants in

the community. In addition, the impact on small and less

conspicuous plant species was likely unnoticed because stud-

ies frequently used aerial photography to estimate changes

in plant abundance.

Grass carp can be considered “selective generalists” in

their foraging behavior because they eliminate species in or-

der of decreasing palatability (Colle et al. 1978, Van Dyke et

al. 1984, Leslie et al. 1987). More than 50 genera of food

items, including aquatic macrophytes, algae, invertebrates

and vertebrates, were reported to be eaten by grass carp (Ta-

ble 2). Feeding preference is one of the best-studied aspects

of grass carp biology; however, contradictory evidence exists

for several plant species this ﬁsh consumes (Tables 2 and 3;

also see Bonar et al. 1990, Cooke et al. 2005). Hydrilla and

pondweeds (

Potamogeton

spp

) were the most common food

items reported to be eaten by grass carp, and species most

commonly avoided were in the genera

Nymphaea

Potamoge-

ton

Myriophyllum

Nuphar

, and

Typha

. For the same set of

macrophyte species, the order of preference changes under

different environmental conditions, most likely determined

by ease of mastication (Wiley et al. 1986, Pine et. al 1989, Bo-

nar et al. 1990). Cellulose, silica, and iron content were

shown to be the best predictors of unpalatability, whereas cal-

cium and lignin were positively correlated with consumption

rates (Bonar et al. 1990). Predictions of the order of plant

elimination in the ﬁeld still have a large degree of uncertain-

ty; the situation may be improved by a series of ﬁeld studies

across a range of environmental conditions.

Habitat heterogeneity

Aquatic plants provide habitat heterogeneity important at

both system (i.e., among plant beds) and micro (i.e., within

plant beds) scales. The level of this heterogeneity is deter-

mined by the magnitude of available spatial “patchiness”

constituted by unique plant attributes (i.e., stem-leaf mor-

phology and architecture) found in the habitat (Dibble et al.

2006). Variability and juxtaposition among these different

habitat attributes may collectively deﬁne the ecological value

of habitat in a community or ecosystem as a whole (Wiens

1976, Stensen 1980, Holt 1984, Horne and Schneider 1995,

J. Aquat. Plant Manage.

47: 2009. 3

Moloney and Levin 1996). Species diversity is positively cor-

related with habitat complexity, and increasing heterogene-

ity among habitats at a landscape scale is a common objective

in ecosystem management (Bookhout 1996). Direct impacts

by grass carp on habitat heterogeneity, even though ecologi-

cally important, were not adequately assessed in the research

we reviewed.

Similarly, the heterogeneity at a smaller scale within aquat-

ic plants is just as important for habitat structure (Dionne

and Folt 1991, Lillie and Budd 1992, Budd et al. 1995), yet

grass carp impacts on structure have gone unmeasured. This

level of habitat heterogeneity can be determined as spatial

complexity (e.g., plant stem density or frequency of interstic-

es; Lynch and Johnson 1989, Dibble et al. 1996) and is equal-

ly important to individual organisms (Anderson 1984, Diehl

1988, Dibble and Harrel 1997, Pedlow et al. 2006) and col-

lectively to populations (Persson and Eklov 1995). Spatial

complexity in aquatic habitats is important for predator

avoidance and ontogenetic niche shifts (Werner et al. 1977,

Lodge et al. 1988, Persson and Crowder 1997) and, at least

theoretically, greater macrophyte densities allow higher equi-

librium densities of both ﬁsh and macroinvertebrates (Diehl

and Kornijów 1997). A few investigations on grass carp hy-

pothesized mechanisms of trophic interactions and popula-

tion dynamics (Bettoli et al. 1991, 1992, 1993), yet no

attempt was made to measure heterogeneity at this level or

validates the mechanism that explained the effects. Even

without complete vegetation removal, preferential feeding

may signiﬁcantly affect habitat heterogeneity.

The problem of reaching the desired habitat heterogene-

ity is complicated by the inability to accurately predict effec-

tive stocking densities. Despite a relatively high number of

studies published on this topic, speciﬁc stocking densities

that would result in complete elimination of a speciﬁcally tar-

geted plant cannot accurately be predicted across a range of

different plants and environmental conditions. Partial con-

trol of vegetation is rarely achieved with grass carp (Petr

2000, Bonar et al. 2002. After studying 38 lakes in Florida,

Hanlon et al. (2000) concluded that the relationship be-

tween stocking density and plant abundance was unpredict-

able except for maximum stocking density that consistently

resulted in complete eradication of macrophytes. The prob-

ABLE

1. G

RASS

CARP

IMPACT

THE

COMMUNITY

Topical emphasis References

Effects on Community Structure

Algae biomass/phytoplankton 8, 11, 24, 30, 32, 41, 44, 48, 53, 55, 56, 61, 63, 65, 75, 110, 114, 123, 124, 137, 161

Crayﬁsh 27, 41, 123

Detritus 61, 113

Fish 3, 4, 8, 9, 10, 11, 16, 19, 22, 26, 42, 46, 50, 52, 53, 54, 55, 56, 58, 61, 62, 63, 67, 73, 78, 80, 85, 86, 92, 94, 99, 100,

104, 105, 108, 113, 121, 123, 141, 143, 151, 157

Habitat alteration 3, 10, 11, 16, 43, 50, 112, 114, 119, 139

Grass shrimp 45, 143

Macroinvertebrates 6, 8, 10, 27, 32, 41, 53, 55, 63, 65, 73, 96, 97, 105, 108, 112

Native plants 30

Periphytic algae 30, 32, 115

Phytoplankton diversity 44, 61, 160

Plant abundance 8, 11, 12, 13, 19, 59, 58, 64, 65, 81, 91, 112, 127, 128, 135, 160

Plant biomass 19, 60, 61, 66, 70, 74, 81, 83, 90, 94, 97, 100, 104, 110, 121, 134, 160, 161

Plant composition 104, 127, 150, 161

Plant diversity 11, 12, 13, 19, 48, 81, 91, 97, 100, 161

Plants, percent coverage 55, 58, 60, 63, 64, 97, 108, 112, 135, 137, 155, 158, 160, 161

Standing crop 84

Seasonal effects on plants 19, 71, 72, 76

Snails 6

Zoobenthos 123, 160

Zooplankton 32, 44, 54, 55, 63, 65, 96, 97, 98, 101, 105, 108, 110, 115

Water quality 4, 7, 8, 11, 17, 18, 19, 30, 31, 32, 44, 47, 48, 53, 54, 55, 58, 61, 63, 65, 66, 67, 74, 75, 79, 94, 95, 96, 98, 100, 101,

104, 105, 106, 108, 110, 113, 114, 115, 121, 123, 124, 137, 143, 150, 160

Effects on Community Process

Carbon ﬂow 8, 19

Eutrophication 96, 114

Food chains 8, 10, 62, 123

Lake productivity 8, 19, 49, 55

Nutrient loading 18, 24, 86, 113, 114, 124

Photosynthesis 8, 53

Primary production 97, 98, 101, 104, 106, 107, 108, 121, 124

Reduction of buffer capacity 18

Shoreline erosion 33

Streamﬂow 96

Weevill activity 45

Reference numbers correspond to the number preceding citations in the bibliography listed in the appendix.

J. Aquat. Plant Manage.

47: 2009.

ABLE

2. L

IST

FOOD

ITEMS

(

GENERA

)

REPORTED

EATEN

GRASS

CARP

Genus Reference

Alisma

132

Alternanthera

112

Anax

113

Azolla

35, 123, 131

Bacopa

142

Bimaslur

113

Brasenia

112

Bufo

113

Cabomba

31, 107, 108, 112, 155

Callitriche

15, 123, 132

Carex

123, 126, 142

Ceratophyllum

4, 10, 19, 35, 48, 55, 60, 64, 79, 93, 95, 98, 101, 104, 107, 121, 123, 126, 127, 131, 132, 134, 150, 155

Chara

15, 35, 48, 66, 72, 75, 81, 95, 99, 123, 126, 128, 130, 142, 143, 146, 160, 164

Cladophora

131, 160, 161

Egeria

84, 91, 95, 134

Eichhornia

26, 35, 45, 112, 131

Eleocharis

40, 84, 87, 112, 142, 143, 161

Elodea

15, 19, 71, 81,93, 95, 99, 104, 107, 121, 123, 126, 131, 143, 163

Ephemera

113

Glyceria

Halophila

123

Hydrilla

2, 4, 7, 10, 13, 17, 18, 20, 31, 33, 35, 44, 48, 49, 54, 55, 58, 62, 63, 64, 70, 78, 79, 91, 95, 96, 98, 105, 108, 120, 123, 133, 135, 155, 158

Hydrocharis

123, 126

Hygrophila

Juncus

123, 126

Lagarosiphon

119

Lemna

15, 35, 74, 107, 123, 126, 131, 132

Limnobium

131

Limnophila

123

Mayaca

155

Myriophyllum

4, 10, 15, 18, 35, 48, 55, 64, 66, 71, 75, 93, 95, 96, 99, 101, 107, 123, 126, 130, 132, 134, 142, 155

Nuphar

112

Najas

11, 19, 35, 60, 104, 107, 121, 123, 131, 142, 143, 155, 164

Nasturtium

123, 126

Nechamandra

123

Nitella

15, 84, 123

Notropis

113

Nymphaea

131

Ottelia

123

Phragmites

110, 123, 126

Pistia

35, 131

Pithophora

123

Polygonum

99, 142, 143

Potamogeton

11, 12, 15, 18, 19, 54, 66, 71, 72, 74, 75, 83, 84, 93, 95, 96, 99, 104, 107, 121, 123, 126, 127, 128, 130, 131, 132, 143, 150, 161, 164, 166

Ranunculus

Rhizoclonium

Ruppia

131

Sagittaria

40, 142

Salomia

123

Salvinia

123

Sparganium

123, 132

Spirodela

123

Spirogyra

123, 131

Trapa

101, 123

Typha

99, 123, 126, 132

Utricularia

87, 107, 123

Vallisneria

123

Wolfﬁa

35, 123

Zannichellia

132

Zygnema

160

Reference numbers correspond to the number preceding citations in the bibliography listed in the appendix.

Non-plant food item.

J. Aquat. Plant Manage.

47: 2009. 5

lem of appropriate vegetation control is exacerbated by the

long life span of this ﬁsh; grass carp live longer than 10 years,

and they have been shown to persist in a lake for at least 2

years after complete removal of the invasive plant it was

stocked to control (Kirk et al. 2000, Kirk and Socha 2003).

Long persistence in the environment may also hinder future

native macrophyte revegetation efforts if the policy or stake-

holder interests change.

Early life stages

Most literature discussed only direct impacts relevant to

adult grass carp and neglected potentially important direct

impact of early life stages of carp on other ﬁshes. Grass carp

stocked for plant control is usually >200 mm in length to re-

duce mortality due to predation (Pierce 1983, Cassani 1996);

however, mounting evidence suggests that naturalized popu-

lations of grass carp are reproducing in the United States

(Connor et al. 1980, Pﬂieger and Grace 1987, Brown and

Coon 1991, Raibley et al. 1995). In fact, one recent study re-

ported juvenile grass carp in two rivers in Oklahoma previ-

ously deemed unsuitable for grass carp reproduction

(Hargrave and Gido 2004).

Vegetated habitats provide important nursery grounds for

many native ﬁshes (Gregory and Powles 1985, Chubb and

Liston 1986, Dibble et al. 1996b), and competition for avail-

able food and habitat among and between early life stages of

these ﬁshes can be intense and critical to growth and survival

(Werner and Hall 1979, Mittelbach 1981, Diehl 1993). In-

creases in the number of young non-native ﬁsh may exacer-

bate competition and niche overlap. Larval and juvenile

grass carp are not herbivorous and have been shown to feed

on zooplankton, insect larvae, chironomids, cladocerans,

and copepods (Chilton and Muoneke 1992, Cudmore and

Mandrak 2004). Young grass carp may therefore alter trophic

dynamics within communities by directly competing for food

with native ﬁshes and their larvae.

Indirect impacts

Community structure

Secondary effects from a primary disturbance may be

stronger in aquatic communities than the more easily mea-

sured direct impacts (Kerfoot and Sih 1987). There is indis-

putable evidence for presence of trophic cascades in aquatic

systems (Brett and Goldman 1996), and some of the stron-

gest cascades are observed in benthic habitats of lakes (Shu-

rin et al. 2002). Presence of novel phytophagous ﬁsh

exceeding gape size of predator has a potential to involve

novel energy pathways (e.g., with more energy ﬂowing to-

wards detrital food chain), which may strongly affect rates of

nutrient cycling. Increase in nutrient cycling leads to re-

duced resilience of an ecosystem (Wetzel 2001), often mani-

fested in population explosions and subsequent crashes of

dominant taxa. Because macrophytes play an important role

in benthic-pelagic coupling by subsidizing pelagic ﬁsh popu-

lations and affecting nutrient loading (Schindler and

Scheuerell 2002), it is natural to expect that effects of grass

carp would propagate beyond the littoral zone and change

the role of benthic subsidies to the pelagic habitat of lakes.

Mitzner (1978) demonstrated that introduction of grass carp

resulted in reduced primary production, possibly due to de-

creased littoral-pelagic coupling (Lodge et al. 1988).

Grass carp may be viewed as a novel keystone species that

reduces spatial heterogeneity, and the resulting loss of com-

plex habitat can potentially inﬂuence exploitative competition

and other interactions among resident species. This is an ex-

ample of how the indirect effect of a large herbivore may be

transmitted through a resource base, consequently altering

the community structure. Other behavioral alterations due to

the presence of large ﬁsh, whether they are direct predators or

not, can impact populations (Sih 1980, Sih et al. 1985, Miller

and Kerfoot 1987) and potentially alter ecosystem processes.

Secondary changes in aquatic vertebrate and invertebrate

communities have been documented after grass carp intro-

ductions (see next section). Some observed effects are not

consistent across different studies, which may be an indication

of our limited understanding of the underlying mechanisms.

Macroinvertebrate populations

Aquatic plants form a base for macrophyte-periphyton-

grazer complex (Carpenter and Lodge 1986) and support

high densities of macroinvertebrates by providing them with

food, habitat, and refuge from predation (reviewed in Diehl

and Kornijów 1997). Changes in vegetation due to grass carp

ABLE

3. A

QUATIC

PLANTS

REPORTED

AVOIDED

GRASS

CARP

Plant Genera Reference

Alternathera

123

Brasenia

107

Cabomba

131

Ceratopohyllum

40, 161, 164

Chara

Cladium

Echinodorus

107

Egeria

Eichhornia

123

Eleocharis

107

Jussiaea

165

Lemna

166

Myriophyllum

54, 81, 123, 131, 161, 164

Najas

Nelumbo

107

Nuphar

31, 81, 108, 109

Nymphaea

31, 93, 107, 108, 109, 123

Nymphoides

109, 123

Orontium

107

Phragmites 160

Pistia 123

Polygonum 107, 123

Potamogeton 35, 40, 107, 166

Ranunculus 109, 165

Sagittaria 107, 131

Salvinia 35

Scirpus 107

Typha 31, 107, 108

Vallisneria 48

aReference numbers correspond to the number preceding citations in the

bibliography listed in the appendix.

6J. Aquat. Plant Manage. 47: 2009.

foraging lead to decreased macroinvertebrate diversity and

abundance (Vinogradov and Zolotova 1974). Due to de-

crease in attachment substrate typically provided by vegetat-

ed habitat, richness and abundance of epiphytic

macroinvertebrates can decrease, whereas the number of

benthic invertebrate species can increase (Martin and Shire-

man 1976, Leslie and Kobylinski 1985, Klussman et al. 1988,

Kirkagac and Demir 2004). However, Fedorenko and Frazer

(1978) reported that benthic invertebrates also decreased af-

ter vegetation removal by grass carp, possibly due to direct

competition, low food availability, and increased predation

due to the loss of refuge.

Fish populations

In general, when vegetated habitats become too spatially

complex, ﬁsh growth is negatively impacted due to reduced

food availability and decreased feeding efﬁciency (Crowder

and Cooper 1982, Savino and Stein 1982, Anderson 1984).

Moderate (20%) removal of overly dense vegetation resulted

in improved growth of some age classes of bluegill (Olson et

al. 1998); however, further reduction in aquatic plant density

and the corresponding decrease in spatial complexity results

in increased competition for limited food sources and refugia

(Mittelbach 1988). Thus, plant levels at either extreme of the

density spectrum may decrease ﬁsh growth and survival and,

ultimately, alter population dynamics within the community

(Adams and DeAngelis 1987, Savino et al. 1992, Diehl 1993).

As a general tendency, a decrease in the abundance of ﬁsh

species are dependent on aquatic plants, such as largemouth

bass (Micropterus salmoides) and other sunﬁshes (Lepomis spp.),

whereas non-phytophyllic species, such as gizzard shad (Dor-

osoma cepedianum) and silversides (Labidesthes spp.), tend to in-

crease in abundance (Ware and Gasaway 1978, Klussman et

al. 1988, Maceina et al. 1991, Bettoli et al. 1992,). Bettoli et al.

(1993) observed a radical change in ﬁsh community follow-

ing grass carp introduction, with a decline in the total num-

ber of species over a 7-year period (Table 4). Most notable

declines were observed for Lepomis spp., crappie (Pomoxis

spp.), brook silversides (Labidesthes sicculus), and juvenile

largemouth bass. Colle and Shireman (1994) reported that

after complete elimination of vegetation by grass carp, ﬁsh

harvest declined, and several species had disappeared.

In contrast, Killgore et al. (1998) observed no change in

the number of littoral species and an increase in the total

ﬁsh catch after hydrilla control by grass carp, although the

mean total length of the largemouth bass declined (Table 4).

This study was unusually successful in achieving intermediate

levels of vegetation control, a result that may not be easily ex-

trapolated to many other situations.

Other aquatic vertebrates

Previous work has evaluated indirect impacts of grass carp

on waterfowl, suggesting that abundance of bird species can

be reduced in the presence of grass carp due to shifts in

plant community and competition for preferred food plants

(Gasaway and Drda 1976, Johnson and Montalbano 1984,

1987, Leslie et al. 1987, McKnight and Hepp 1995). Howev-

er, no study speciﬁcally addressed grass carp impact on other

vertebrates (e.g., aquatic mammals, reptiles, and amphibi-

ans). Many of these animals are highly dependent on vege-

tated habitats for food and protection from predators, and

macrophytes are critical to their survival. Salamanders feed

on small prey species living in aquatic plants, and larval stag-

es of amphibians rely on these habitats to avoid predation

(Brophy 1980, Zaret 1980).

Muskrats (Ondatra zybethicus), beaver (Castor canadensis),

and nutria (Myocastor coypus) rely heavily on aquatic plants

(Chabreck 1988, Fredrickson and Laubhan 1996), and more

research is needed to quantify how changes in aquatic plants

alter habitat and distribution of these animals. A better un-

derstanding of how grass carp impact animal distribution will

improve the management of these ecosystems; this is espe-

cially important for controlling exotic species such as nutria.

Indirect effects operate at different temporal and spatial

scales. Parameters that validate those mechanisms are not

easily measurable and usually require a period of time before

response is detected (Miller and Kerfoot 1987), which may

explain why these effects are frequently ignored or inade-

quately tested. Nevertheless, they need to be incorporated

into the designs of future experiments attempting to predict

and explain how grass carp impact aquatic communities.

Water quality

Aquatic plants decrease sediment resuspension, play an

important role in nutrient cycling (Carpenter and Lodge

1986, Barko and James 1997), and create microclimates in

the littoral zone (Lodge et al. 1988). Submerged macro-

phytes are responsible for several positive feedback mecha-

nisms promoting retention of the vegetated state (Scheffer

and Jeppesen 1997, Van Donk 1997), particularly important

under the conditions of increasing eutrophication. Shallow

TABLE 4. IMPACT OF GRASS CARP ON OTHER FISHES.

Topical emphasis References a

Populations 4, 8, 9, 10, 11, 16, 46, 50, 52, 53, 54, 78, 92, 116,

141

Density/abundance 53, 55, 56, 58, 62, 67, 85, 92, 108, 123, 141, 151,

157

Biomass 8, 50, 55, 58, 61, 78, 81, 92, 100

Diversity 50, 55, 56, 62, 100, 157

Production (kg/ha) 53, 80, 123

Total stand. crop (kg/ha) 58, 62, 63, 73, 78, 108, 123

Weight 92, 105

Relative weight 58

Length 92, 105, 157

Distribution 85, 151

Vulnerability to predation 85

Diets 3, 10, 26, 85, 92, 110, 113

Growth 11, 22, 26, 42, 67, 80, 85, 86, 99

Condition 50, 54, 78, 85, 92, 105, 143

Recruitment 42, 67, 78, 92, 99

Reproductive success 62, 73, 92, 123

Male/female ratio 92

Spawning impacts 16, 81, 123

Angler success 19, 50, 62, 94, 99, 104, 121

aReference numbers correspond to the number preceding citations in the

bibliography listed in the appendix.

J. Aquat. Plant Manage. 47: 2009. 7

lakes provide one of the most dramatic examples of a cata-

strophic shift when they suddenly change from clear-water

vegetated state to an alternative stable state, turbid and un-

vegetated, in response to gradual changes in conditions,

such as nutrient loading or macrophyte removal (Scheffer et

al. 2001).

Detrimental changes in water quality parameters (in-

crease in nitrite, nitrate, phosphate concentrations) follow-

ing vegetation control by grass carp were reported in most

studies that evaluated water quality (Table 5; Shireman and

Smith 1983, Kirkagac and Demir 2004). These changes re-

sult from sediment resuspension during feeding and fecal

matter deposition by carp as well as collapse of mechanisms

responsible for maintenance of the vegetated state due to

removal of macrophytes. The rate at which aquatic plants

are eliminated determines the magnitude of impact (Hest-

land and Carter 1978, Lembi et al. 1978, Leslie et al. 1983,

1987, Richard et al. 1984, 1985). These changes in water

quality are often followed by algal blooms (Vinogradov and

Zolotova 1974, Canﬁeld et al. 1983, Klussman et al. 1988,

Shireman and Smith 1983), which in most lakes signal a

shift to an alternative stable state (Scheffer and Jeppesen

1997). Increased rates of nutrient cycling after resuspen-

sion of sediments lead to decreased ecosystem stability

(Wetzel 2001). When weighing pros and cons of complete

macrophyte eradication, note that these water quality

changes are often irreversible on relatively long time scales,

even after herbivorous ﬁsh are removed (Scheffer et al.

2001).

Other considerations

Many natural freshwater lakes were isolated for some peri-

od of time and may harbor genetically distinct and/or locally

rare populations of plants and animals. While it is not clear

whether other methods of vegetation control or the invasion

itself may have an effect just as detrimental as vegetation con-

trol by grass carp, the issue of potential impact on such popu-

lations needs to be addressed in the future if carp is to be

used in systems other than ponds.

According to the invasional meltdown hypothesis, as more

non-native species are introduced into the system, popula-

tions of resident native species are increasingly disrupted,

and the community becomes more susceptible to future inva-

sions (Simberloff and Von Holle 1999, Ricciardi 2001). As

the history of biological introductions has shown, these as-

pects are very difﬁcult to forecast and assess (Simberloff and

Stiling 1996). Until proven otherwise, such possibility exists

for grass carp introductions; for instance, frequent distur-

bance of sediment and vegetation may in fact promote fur-

ther plant invasions. This may be especially true when grass

carp is used without simultaneous mitigation of factors caus-

ing nuisance species overgrowth (e.g., eutrophication or fre-

quent disturbance).

Current stocking practices

Grass carp are now recorded in 45 states (Mitchell and

Kelly 2006). In some states, only triploid carp can be stocked

TABLE 5. PHYSICAL PARAMETERS MEASURED TO DETERMINE IMPACTS BY GRASS CARP ON WATER QUALITY.

Parameter References a

Alkalinity 7, 17, 19, 47, 53, 54, 55, 58, 63, 66, 75, 94, 95, 104, 114, 121, 143

Ammonia nitrogen 55, 75, 108, 113, 114, 123, 137

Calcium 17, 47, 48, 58

Carbonates 11, 44, 55, 58, 63, 66, 75, 95, 115

Chlorophyll 4, 17, 18, 30, 31, 32, 44, 54, 58, 65, 67, 114, 137, 143, 150, 160

CO2 110

Conductivity 7, 17, 54, 55, 58, 63, 66, 95, 108, 114, 115

Dissolved oxygen 7, 44, 47, 18, 54, 66, 95, 96, 100, 101, 105, 110, 114, 116

Dissolved organic matter 8, 79, 98, 106, 115

Iron 115, 123

Kjeldahl nitrogen 18, 54, 66, 95, 96, 115

Light compensation point 105

Magnesium 17, 47, 48, 58, 115, 123

Nitrates/Nitrites 19, 31, 44, 47, 48, 54, 55, 65, 75, 104, 113, 114, 137, 160

Oxygen demand 19, 47, 53, 104

pH 7, 17, 44, 47, 48, 53, 54, 63, 66, 95, 96, 104, 105, 108, 113, 114, 143

Phosphate/Phosphorous 11, 17, 18, 19, 31, 44, 47, 48, 54, 55, 58, 61, 63, 65, 67, 75, 79, 98, 100, 104, 106, 108, 113, 114, 115, 123, 124, 137, 160

Potassium 17, 48, 58, 75, 105, 113, 115, 123

Sulfate 47, 55, 105, 115

Sulfur bacteria 48

Tannin-Lignin levels 31, 47, 108

Temperature 54, 113

Total nitrogen 5, 17, 18, 48, 58, 63, 100, 108

Total photosynthetic pigments 53

Turbidity 18, 19, 47, 48, 53, 54, 66, 95, 104, 108, 110, 123, 143

Water clarity/Secchi 55, 58, 98, 114, 137

aReference numbers correspond to the number preceding citations in the bibliography listed in the appendix.

8J. Aquat. Plant Manage. 47: 2009.

for vegetation control, and the procedure for ensuring infer-

tility is tightly regulated by the U.S. Fish and Wildlife Service.

Only certiﬁed triploid grass carp can be possessed west of the

Continental Divide and in the Rio Grande Basin (California

Laws: Fish and Game Code, Section 6440-6460). Alaska,

Maine, Maryland, Massachusetts, Michigan, Minnesota, Mon-

tana, Oregon, North Dakota, Rhode Island, Vermont, and

Wisconsin banned both diploid and triploid grass carp (re-

viewed in Mitchell and Kelly 2006), while some states allow

possession of diploid grass carp for aquaculture purposes,

production of triploids, or even vegetation control.

In states where grass carp possession is regulated, a special

permit (from the departments of natural resources) is re-

quired for stocking grass carp. Often, however, a free permit

can be obtained by anyone who demonstrated a need to con-

trol aquatic vegetation. Satisfactory guidelines have been de-

veloped from the standpoint of limited knowledge about

ecological effects of this introduction (Table 6). These guide-

lines, if followed closely, may help ensure that, if deleterious

effects occur after grass carp introduction, such effects are at

least contained to small ponds not connected to any natural

aquatic systems (also see Cooke et al. 2005, p. 443). The rec-

ommended maximum stocking density is sufﬁciently low to

prevent, in most cases, complete vegetation removal, and ad-

equate precautions are taken with respect to rare and endan-

gered species. Also, this publication provides the pond

owner with sufﬁcient information on the importance of

aquatic vegetation and possible changes in water quality after

vegetation control by grass carp. Due to its generalist habits,

grass carp is not well-suited for selective control of invasive

aquatic plants when some level of native plants is desired.

Other Asian carps, such as black (Mylopharyngodon piceus

Richardson), silver (Hypophthalmichthys molitrix Valenci-

ennes), and bighead (H. nobilis Richardson) have become in-

vasive species of special concern (reviewed in Schoﬁeld et al.

2005), and there is a high likelihood that asian carp may be-

come invasive as well. Some populations have already natu-

ralized, and it is now critical to study their effects on

ecosystems as well as make it unlawful to continue stocking

diploid grass carp. The importance of changing regulations

in states that still allow possession and stocking of diploids

cannot be overemphasized (also see Cooke et al. 2005, p.

437).

Recommendation for future research

More research is needed to investigate both direct and in-

direct impacts of grass carp, with greater emphasis on indi-

rect impacts. Future investigations need to better quantify

these impacts within and across vegetated habitats for a bet-

ter understanding of community processes. Improved mea-

surement of habitat heterogeneity using new descriptors

(e.g., complexity indices, fractal dimension) is essential for

an accurate assessment of habitat changes and their effect on

community. Additional information is also required to deter-

mine how grass carp impact multi-species interactions (e.g.,

interspeciﬁc competition and trophic/predator-prey interac-

tions) and individual behavior (e.g., foraging efﬁciency,

predator avoidance, and habitat use). Future investigations

need to address impacts of all life stages of grass carp, espe-

cially in systems where reproduction of naturalized popula-

tions has been conﬁrmed. It is important to study ecosystem

effects of grass carp, such as changes in rates of nutrient cy-

cling, nutrient compartmentalization, and habitat coupling.

Data are needed to determine appropriate levels of abun-

dance and diversity at which aquatic plants should be main-

tained to prevent a shift to turbid state and negative effects on

animal communities. This review shows that aquatic macro-

phytes are important for habitat heterogeneity and ecological

stability; however, it is difﬁcult to achieve optimal habitat het-

erogeneity and/or only target invasive plants with this non-se-

lective biocontrol agent. Further study of how grass carp

feeding preferences across a range of environmental condi-

tions inﬂuence spatial attributes of aquatic habitats will help

predict community responses to changes in habitat heteroge-

neity. Meanwhile, innovative research is needed to ﬁnd suc-

TABLE 6. INFORMATION FROM “GRASS CARP IN NEW YORK PONDS”, PUBLICATION OF NEW YORK STATE DEPARTMENT OF ENVIRONMENTAL CONSERVATION, DIVISION

OF FISH, WILDLIFE & MARINE RESOURCES.

“. . . approve and issue permits for stocking of up to 15 United States Fish and Wildlife Service certiﬁed triploid grass carp [from approved suppliers

possessing a valid permit to import and sell triploid grass carp in New York State] per surface acre for aquatic plant management purposes in ponds ﬁve (5)

acres or less in size which lie wholly within the boundaries of lands privately owned or leased by the individual making or authorizing such treatments if:

•aquatic plants targeted for control signiﬁcantly impair the intended use(s) of the pond;

•the pond harbors no species of wildlife, ﬁsh, shellﬁsh or crustacea identiﬁed by the Department as being endangered,

threatened or special concern; or any species of plant identiﬁed as being endangered, threatened or rare;

•the pond is not contiguous to or part of a New York State regulated freshwater wetland.

•is not an impoundment or natural pond on a permanent stream or a source of a permanent stream.

•at least two years have elapsed since the last stocking of triploid grass carp

“Triploid grass carp are extremely potent plant consumers. If overstocked, they are capable of eradicating all plants from a pond for periods exceeding 10

years. Besides the obvious impact such complete plant removal will have on vegetation-dependent ﬁsh and wildlife, total devegetation of a pond can also

result in the development of severe algae blooms, foul smells and an overall decline in water clarity. To minimize or prevent such adverse impacts, plant

populations should be maintained at approximately 20-30% of the pond’s surface area.

Due to various factors that impact triploid grass carp feeding, it is impossible to precisely predict the exact number of ﬁsh to stock to achieve the 20-30%

plant coverage target. The only way to prevent excessive plant control is through use of an incremental approach. This approach involves the stocking of

triploid grass carp at the stocking rates suggested below, followed by a two-year waiting period for the ﬁsh to achieve maximal control. Then, if needed,

more ﬁsh are added in small increments at two-year intervals until plant populations are reduced to the 20-30% threshold.”

J. Aquat. Plant Manage. 47: 2009. 9

cessful methods to provide more accurate control for different

levels of plant growth, abundance, and composition. Detailed

evaluation of community responses to differential stocking

rates is needed, as are the techniques to control current grass

carp populations already released into natural systems.

Understanding ecological impacts is paramount to appro-

priate management of aquatic communities. Current data

are not sufﬁcient to adequately answer important questions

about use of grass carp as a biocontrol agent for aquatic

plants. The problem of assessing all possible impacts is not

unique to grass carp: it has been shown for most introduced

biocontrol agents (reviewed in Simberloff and Stiling 1996).

The extent to which these approaches are used in future re-

search will determine the amount of knowledge gained rela-

tive to understanding the ecological impacts of grass carp on

aquatic communities. Until these data are collected, a more

conservative approach should be used when developing

guidelines for grass carp use.

ACKNOWLEDGMENTS

We appreciate the help provided by J. Cruickshank, E.

Forrester, R. Kimbrough, B. LaValley, and J. O’Keefe for

their assistance in the retrieval and initial analysis of litera-

ture, and S. Harrel and P. Smiley for editorial comments pro-

vided on an earlier draft of this manuscript. This manuscript

was signiﬁcantly improved by the suggestions of three anony-

mous reviewers. The Aquatic Ecosystem Restoration Founda-

tion funded an earlier review of the literature that was

incorporated in this manuscript. We thank J. Madsen and the

GeoResources Institute at Mississippi State University for sup-

port and the U.S.G.S. Invasive Species Science Program for

funding this project.

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APPENDIX

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444.

A Triploid Grass Carp

Risk Analysis Speciﬁc to Florida

PAUL W. ZAJICEK1, T. WEIER2, S. HARDIN3, J. R. CASSANI4 AND V. MUDRAK5

ABSTRACT

Three hydrilla (Hydrilla verticillata) biotypes are resistant

to ﬂuridone, the principal herbicide used in Florida. Be-

cause of an anticipated demand for triploid grass carp

(Ctenopharyngodon idella), a risk analysis was conducted to ex-

amine the use of triploid grass carp to control hydrilla in

large (>200 ha), open systems in Florida. An expert panel

utilized the Generic Nonindigenous Aquatic Organisms Risk

Analysis Review Process developed by the Aquatic Nuisance

Species Task Force to assess ﬁve hydrilla management op-

tions. Speciﬁcally, the panel assessed the risk of (1) eliminat-

ing all vegetation for three years or more; or (2) vegetation

coverage exceeding 50% for ﬁve consecutive years. Herbi-

cide application, followed by stocking low levels of triploid

grass carp and subsequent herbicide treatment, was consid-

ered to be a lower risk option to achieve hydrilla manage-

ment objectives. The expert panel emphasized the necessity

of implementing well-supported system management and

monitoring and determining stocking rates on a lake-by-lake

basis.

Key words: aquatic macrophytes, biological control,

Ctenopharyngodon idella, fluridone resistance, Hydrilla verticil-

lata, risk analysis.

INTRODUCTION

Florida has an abundance of shallow (<5m) natural lakes

with diverse emergent and submersed plant communities.

1Division of Aquaculture, Florida Department of Agriculture and Con-

sumer Services, 1203 Governor’s Square Blvd, Tallahassee, FL 32301, zaji-

cep@doacs.state.ﬂ.us.

2888 North Almeda Street, Apartment 409E, Los Angeles, CA 90012.

3Florida Fish and Wildlife Conservation Commission, 620 South Merid-

ian Street, Tallahassee, FL 32399-1600.

4Lee County Hyacinth Control District, P.O. Box 60005, Fort Myers, FL

33906.

5U.S. Fish and Wildlife Service, Warm Springs Technology Center, 5308

Spring Street, Warm Springs, GA 31830. Received for publication May 1,

2008 and in revised form November 30, 2008.

J. Aquat. Plant Manage. 47: 15-20

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Mar 2023
BIOL INVASIONS

Understanding the timing and drivers of migration can be beneficial for improving response efforts aimed at reducing invasive species densities. Efforts by management agencies to remove grass carp (Ctenopharyngodon idella), an invasive species to the Laurentian Great Lakes, have been ongoing in Lake Erie tributaries since 2018. To bolster efforts, deployment of a non-physical barrier has been proposed downstream of a known grass carp spawning location near Brady’s Island (BI) in the Sandusky River, OH, USA to limit recruitment. However, knowledge of grass carp migratory timing, the environmental variables that cue carp migration, and the potential effects the barrier might impose on native fish [e.g., walleye (Sander vitreus)] movements would help inform barrier deployment and scheduling. We used detection data from grass carp (n = 29) and walleye (n = 84) tagged with acoustic transmitters to address four objectives: (1) quantify interannual variation (years = 2015–2021) of grass carp migration timing to BI; (2) evaluate timing of different grass carp movement modalities (residents and migrants); (3) assess overlap in migration timing with native walleye, and (4) evaluate environmental cues of grass carp migration to BI. Median grass carp arrival at BI occurred within a three-week period (148–165 Julian days), suggesting that deploying a barrier immediately prior to this time frame may be effective for deterring grass carp spawning. Temperature, photoperiod, and discharge influenced grass carp migration timing given that most arrival events occurred at daylengths > 14.5 h, temperatures exceeding 18 °C, and low discharge events (< 3,000 cubic feet second⁻¹ [CFS]). Minimal interannual variability in migration timing existed for grass carp and walleye over a six-year period. However, the median departure time of walleye was more than 45 days before the median arrival time of grass carp, suggesting a spawning barrier may minimally affect walleye spawning. No differences in arrival timing at BI were observed between grass carp migratory contingents, indicating that if a barrier were deployed in the spring, it would likely affect all grass carp spatial contingents. This work highlights management implications of barrier control efforts of aquatic invasive species and provides insight into the environmental cues that grass carp use for upstream migration.

ВКУСОВЫЕ ПРЕДПОЧТЕНИЯ КАРПОВЫХ РЫБ (CYPRINIDAE). СРАВНИТЕЛЬНОЕ ИССЛЕДОВАНИЕ

Article

Full-text available

Jan 2023

Приведены сведения о вкусовой привлекательности различных веществ (аминокислот, карбоновых и некоторых органических кислот, классических вкусовых веществ) для восьми видов карповых рыб (Cyprinidae) – леща Abramis brama, обыкновенного горчака Rhodeus sericeus amarus, верховки Leucaspius delineatus, золотого карася Carassius carassius, уклеи Alburnus alburnus, ельца Leuciscus leuciscus,голавля L. cephalus и суматранского барбуса Puntigrus tetrazona. Оценён уровень вкусовой чувствительности рыб к некоторым веществам. С привлечением данных по другим видам семейства выполнен сравнительный анализ, который показал высокое видовое своеобразие вкусовых спектров карповых рыб. Не выявлена очевидная связь вкусовых предпочтений с образом жизни рыб, их питанием и филогенетической близостью. Все карповые рыбы удерживают пищевые объекты во рту тем дольше, чем выше их вкусовая привлекательность. Число манипуляций, совершаемых всеми рыбами с пищевым объектом, различается у рыб разного образа жизни и принадлежащих к разным трофическим категориям, но не коррелирует со вкусовыми свойствами объекта. При манипуляциях первое удержание схваченного объекта во рту наиболее длительное, чем последующие. Удержания многократно дольше, если в дальнейшем объект проглатывается, чем при отказе рыб от потребления. Большое сходство поведения, проявляемое карповыми рыбами при оросенсорном тестировании пищи, указывает на консервативность пищевого поведения по сравнению со вкусовой рецепцией. Ключевые слова: карповые рыбы, Cyprinidae, пищевое поведение, вкусовая рецепция, вкусовые предпочтения, вкусовая привлекательность, аминокислоты. DOI: 10.31857/S0042875223010071, EDN: DBWSTD

A restructured Bayesian approach to estimate the abundance of a rare and invasive fsh

Article

Full-text available

Feb 2023
BIOL INVASIONS

Quantifying invasive species abundance informs management and control strategies. However, estimating abundance can be challenging, particularly when dealing with rare species early in the invasion process. Data generated from control strategies, such as removing invasive species, are usually not suited to conventional statistical modelling approaches. Hence, we developed a Bayesian model using data generated by a grass carp (Ctenopharyngodon idella) control program in the Sandusky River, Ohio (USA) for estimating the abundance of rare, invasive species. The model is a restructured N-mixture model modifed to incorporate the data generating process (i.e., setting a trammel net to isolate a sampling area followed by boat-mounted electrofshing). Allowing the estimation of grass carp abundance from the species removal data, which had very few detections relative to the sampling efort. Our results indicated that the average number of grass carp present in the river at any one time did not change substantially from 2018 to 2020. The highest abundance estimates were in the lower and upper-middle segments of the river, suggesting possible recolonization from Lake Erie, and possibly other tributaries. Ultimately, the ability to use species-control data to estimate abundance provides important information for management, particularly for invasive ‘sleeper’ species in freshwater ecosystems.

Aquatic Plant Invasion and Management in Riverine Reservoirs: Proactive Management via a Priori Simulation of Management Alternatives

Article

Full-text available

Dec 2022
Diversity

Negative impacts from aquatic invasive plants in the United States include economic costs, loss of commercial and recreational use, and environmental damage. Simulation models are valuable tools for predicting the invasion potentials of species and for the management of existing infestations. We developed a spatially explicit, agent-based model representing the invasion, growth, and senescence of aquatic weeds as functions of day length, water temperature, water depth, and the response of aquatic weeds to biological control. As a case study to evaluate its potential utility, we parameterized the model to represent two historical invasions (1975–1983 and 2004–2007) of Hydrilla (Hydrilla verticillata (L. fil.) Royle) in Lake Conroe, Texas, USA, and their subsequent biological control using grass carp (Ctenopharyngodon idella). Results of several hypothetical alternative management schemes indicated that grass carp stocking densities needed to control Hydrilla infestation increased exponentially as the lag time between initial invasion and initial stocking increased, whereas stocking densities needed to control infestation decreased as the amount of time allowed to control the infestation increased. Predictions such as those produced by our model aid managers in developing proactive management plans for areas most likely to be invaded.

Sustainable management of non-native grass carp as a protein source, weed-control agent and sport fish

Article

Sep 2022
AQUAC RES

Grass carp, a native Chinese freshwater fish species, has been widely introduced and established worldwide for different purposes (protein source, weed control agent, and sport fish). This species can be very effective in controlling aquatic plants. A few countries, such as Afghanistan, Myanmar, Laos and Vietnam, have cultured grass carp as human food for decades. In contrast, other countries, such as Bangladesh, India, and Iran, initially cultured grass carp as weed control agents and later transitioned to using them as food fish. The uncontrolled population of grass carp and the adverse ecological effects cause concern. Grass carp are a source of nutrients, including essential omega-3 fatty acids, eicosapentaenoicacid (EPA) and docosahexaenoic acid (DHA), which greatly benefit human health. Farming and consuming low trophic-level fish is more sustainable than relying on high trophic-level fish. A sustainable polyculture system yields positive social, economic, ecological and aquaculture outcomes. It involves culturing grass carp together with filter-feeding fish of different ecological requirements, feeding habits and behaviours in the same pond. The application of sustainable feeding materials (e.g., food processing waste and food waste-based fish feed pellets) may significantly improve sustainable aquaculture. It might mitigate the adverse ecological impacts experienced by some countries.

Invasive Carps in the Tennessee–Tombigbee Waterway: An Overview of Historical Information and Recent Activities

Technical Report

Full-text available

Mar 2023

Invasive carps have become established throughout the Mississippi River Basin after escape from aquaculture facilities and intentional stockings. Studies indicate that invasive carps disrupt ecosystems (e.g., habitat disturbance and reduced native species biomass) and threaten recreational and commercial fisheries. This report summarizes historical information and recent monitoring and control activities towards invasive carps in the Tennessee–Tombigbee Waterway, which connects the Mississippi River Basin to the uninvaded Mobile River Basin. Historical information and recent activities do not indicated that invasive carps have become established in the Tennessee–Tombigbee Waterway. However, encounters in the neighboring Pickwick Lake (Tennessee River) and observations of invasive carp movement through coastal waters suggest the risk of invasion is increasing. A coordinated, collaborative effort with dedicated resources is needed to ensure that the Tennessee–Tombigbee Waterway, and indeed coastal waters, do not become invasion highways. Available form: https://ecos.fws.gov/ServCat/DownloadFile/230359

The feeding ecology of grass carp: A review

Article

Dec 2022

As an economically important herbivorous fish, the range of grass carp (Ctenopharyngodon idella) has expanded in the world and its ecological influences have become more evident. Currently, we have embarked on assessing the effect of grass carp on aquatic organisms and water quality by integrating the outcomes from previous ecological studies. Bibliographical data integration shows that aquatic plant preference is likely to be related to the cellulose proportion, calcium, sucrose and citric acid of the aquatic plant. Moreover, pharyngeal teeth and multiple gene copies of taste receptors could help reveal the feeding mechanism of grass carp. The expansion of the number of sweet‐detecting T1R2 genes, and the functional potential of Umami taste receptor T1R3 by calcium‐regulation was speculated on the basis of previous experimental observations of grass carp, suggesting that aquatic plant consumption by this species is tightly associated with the taste receptors. Apart from the competition in living space between grass carp and other fish, the effects of consuming zooplankton and zoobenthos were summarized to reveal general passive feeding of grass carp, as well as the feeding choice in the absence of aquatic plants. Water quality data were gleaned to make comparative analyses between groups stocking with and without grass carp to uncover changes in water physicochemical parameters in short‐ (<1 year) and long‐term impacts. This review provides insight into the grass carp feeding behaviour and mechanisms and it will help find a balance between ecological harmony and the industrial development of grass carp.

Ctenopharyngodon idella (grass carp)

Article

Jan 2022

Vicki Bonham

This datasheet on Ctenopharyngodon idella covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Management, Genetics and Breeding, Economics, Further Information.

Non-native Freshwater Fishes of Iran (Identification, Impacts, Management) ماهیان غیربومی آبهای شیرین ایران (شناخت، اثرات، مدیریت)

Book

Full-text available

Jul 2022

This book tends to investigate various aspects of freshwater non-native fish species in six chapters. In the first chapter, definitions and introductory concepts in this field are discussed. Undoubtedly, one of the most critical aspects of investigating these species’ impacts is recognizing their ecological and socio-economic consequences and is the second chapters’ central objective. In this chapter, several examples of the conducted research on the ecological concepts of alien fishes have been investigated. For sure, dealing with these species will only be possible by setting laws, legislation, and regulations. The third chapter outlines the existing international laws and regulations and national laws and regulations in the United States of America, New Zealand, Germany, Italy, and Iran. Risk assessment protocols are one of the most significant concerns for non-native species, and species distribution modeling is embedded as a tool into them. All of them are discussed in chapter four. Moreover, there have been some efforts to identify different exotic fish species, assess their distribution in Iran, and determine their biological characteristics. Now, the main concern is how to manage these species so that there could be low impacts on natural ecosystems. Chapter five is the subject of the discussion and investigates the different methods of controlling non-native fishes introduced in freshwater ecosystems. Finally, the last chapter is devoted to non-native fishes introduced in the freshwater ecosystems of Iran. In this chapter, different characteristics of these species include taxonomy, identification and morphological characteristics, distribution in the world and Iran, various biological aspects such as habitat, nutrition and reproduction, ecological and socio-economic impacts, and their current status in the country are discussed. An important feature of this chapter is the review of studies on various aspects of these species in the country. ماهیان غیربومی، گونه‌هایی هستند که تصادفی یا عامدانه توسط انسان به مناطقی در بیرون از دامنه طبیعی پراکنش خود وارد شده و در آنجا زیست می‌کنند. برخی از این گونه‌ها به دلیل توانایی‌هایی مانند قدرت تولیدمثل بالا، همه‌‌چیزخواری و تحمل دامنه وسیعی از شرایط محیطی، وقتی به محیط جدیدی وارد می‌شوند باعث ایجاد تغییرات و پیامدهای اکولوژیک گسترده شده و با به مخاطره انداختن گونههای بومی و ایجاد خسارتهای اقتصادی‌-اجتماعی فراوان، به گونه آفت در آن منطقه تبدیل می‌شوند؛ در این صورت به آن‌ها، گونه‌های غیربومی مهاجم گفته می‌شود. رودخانه‌ها و تالاب‌های ایران با عواملی مانند خشکسالی و آلودگی رو‌به‌رو هستند و علاوه بر آن، ورود گونه‌های غیربومی ازجمله ماهیان نیز شرایط را برای این اکوسیستم‌ها بحرانی‌تر کرده است. کتاب حاضر با هدف شناخت هر چه بیشتر ماهیان غیربومی اکوسیستم‌های آب شیرین، بررسی اثرات اکولوژیکی و اقتصادی‌-‌اجتماعی و کنترل و مدیریت این گونه‌ها، به رشته تحریر درآمده است.

Influence of submerged macrophytes on trophic interactions among fish and macroinvertebrates. In Jeppesen

Article

Full-text available

Evaluation of macrophyte control in 38 Florida lakes using triploid grass carp

Article

Full-text available

Jan 2000
J AQUAT PLANT MANAGE

Florida's large number of shallow lakes, warm climate and long growing season have contributed to the development of excessive growths of aquatic macrophytes that have seriously interfered with many water use activities. The introduction of exotic aquatic macrophyte species such as hydrilla (Hydrilla verticillata) have added significantly to aquatic plant problems in Florida lakes. The use of grass carp (Ctenopharyngodon idella) can be an effective and economical control for aquatic vegetation such as hydrilla. Early stocking rates (24 to 74 grass carp per hectare of lake area) resulted in grass carp consumption rates that vastly exceeded the growth rates of the aquatic plants and often resulted in the total loss of all submersed vegetation. This study looked at 38 Florida lakes that had been stocked with grass carp for 3 to 10 years with stocking rates ranging from < 1 to 59 grass carp per hectare of lake and 1 to 207 grass carp per hectare of vegetation to determine the long term effects of grass carp on aquatic macrophyte communities. The median PAC (percent area coverage) value of aquatic macrophytes for the study lakes after they were stocked with grass carp was 14% and the median PVI (percent volume infested) value of aquatic macrophytes was 2%. Only lakes stocked with less than 25 to 30 fish per hectare of vegetation tended to have higher than median PAC and PVI values. When grass carp are stocked at levels of > 25 to 30 fish per hectare of vegetation the complete control of aquatic vegetation can be achieved, with the exception of a few species of plants that grass carp have extreme difficulty consuming. If the management goal for a lake is to control some of the problem aquatic plants while maintaining a small population of predominately unpalatable aquatic plants, grass carp carl be stocked at approximately 25 to 30 fish per hectare of vegetation.

HERBIVOROUS FISHES: Culture and Use for Weed Management

Book

Jun 2019

Comparative effects of grass carp and selected herbicides on macrophyte and phytoplankton communities

Article

Jan 1978
J AQUAT PLANT MANAGE

The use of triploid grass carp, Ctenopharyngodon idella (Val), in the control of submerged aquatic weeds in the Florida Lake, Roodepoort, Transvaal

Article

Jan 1991
WATER SA

Changes in the abundance of two atherinid species after aquatic vegetation removal

Article

Jan 1991

Brook silverside Labidesthes sicculus and inland silverside Menidia beryllina coexisted in Lake Conroe, Texas, for at least 6 years before we began our field sampling in 1980. We hypothesized that an extensive infestation of aquatic vegetation was a critical factor allowing sympatry, because introduced inland silversides have rapidly displaced endemic brook silversides in other, less-vegetated, reservoir systems. We believe that an abundant invertebrate prey base associated with the aquatic vegetation was responsible for a low level of interspecific competition for food resources between the two silverside species in Lake Conroe. After removal of vegetation in 1981-1983 by grass carp Ctenopharyngodon idella, the inland silverside population expanded and the brook silverside population declined. By 1986, brook silversides were rare in seine samples taken from, or near, the main basin of the reservoir and appeared to be restricted to tributaries and coves. Data suggest that food habits of the silverside species diverged after vegetation removal, coincident with declines in the limnetic and littoral invertebrate prey bases. The observed shifts in diets, abundances, and distributions of the two silverside populations were consistent with results predicted by studies on silverside feeding mechanics and the competitive exclusion principle.

Control of submersed weeds by grass carp in waterlily production ponds

Article

Jan 1994
J AQUAT PLANT MANAGE

Fish-Habitat Interactions Mediated via Ontogenetic Niche Shifts

Chapter

Jan 1998

A fundamental characteristic of fish is that individuals increase in size by several orders of magnitude over their ontogeny (Werner, 1988). This increase in size generally means that the individual changes its food resource use during development. The change in resource use can take many different routes involving changes between carnivory and herbivory/detritivory (Gerking, 1994). Commonly, an increase in prey size eaten is observed in connection with the increase in consumer size, which potentially involves a change from zooplanktivory, to ben-thivory, and ultimately, to piscivory (Persson, 1988; Osenberg et al., 1994; Olson et al., 1995). These changes in resource use are, in turn, generally associated with habitat shifts in which complex habitats such as vegetated areas of lakes may function both as a resource base and as a refuge from prédation (Heck and Crowder, 1991; Mittelbach and Osenberg, 1993;Persson, 1993; Olson et al., 1995; Persson and Eklöv, 1995).

The effects of the grass carp on the aquatic macrophytes of four Florida lakes

Article

Jan 1984
J AQUAT PLANT MANAGE

The Effects of Grass Carp on Aquatic Plants, Plankton and Benthos in Ponds

Article

Jan 2004
J AQUAT PLANT MANAGE

The effects of the grass carp (Ctenopharyngodon idella Val.) on aquatic plant biomass, water quality, phytoplankton, chlorophyll a, Zooplankton and benthic fauna were investigated between May and September 2000 in earthen ponds at Cifteler-Sakaryabasi Aquaculture and Research Station. Four earthen ponds with an area of 100 m2 were used and one of them was selected as control. The other ponds were stocked at rates of 200, 400 and 600 fish per ha in May. The survival rate of harvested grass carp was 100% in September and the highest weight gain of 428 g occurred at the minimum stocking rate. Cladophora and Zygnema species of aquatic plants were consumed in June by grass carp; however, Chara was eliminated completely by August. At the end of the stocking period, Phragmites was the only plant not consumed by the grass carp. Plant biomass increased 1.4 times in the pond without grass carp but was decreased 2.5 times in the ponds stocked with 200 and 400 grass carp per ha and 4 times in the pond stocked with 600 grass carp per ha. The lowest values of nitrite-nitrogen, nitrate-nitrogen, and total phosphate were measured in the pond without grass carp (p < 0.05). The highest values of phytoplankton, zooplankton, benthic fauna abundance and chlorophyll a were found in the ponds with fish (p < 0.05).

Ecological Impact of Grass Carp: A Review of the Available Data

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