Aristichthys nobilis (Richardson, 1845), Leuciscus nobilis Richardson, 1845

Nonindigenous Occurrences:

Bighead carp were first imported into the United States in 1973 by a private fish farmer in Arkansas as a potential biological control agent to improve water quality and increase fish production in culture ponds (Conover et al 2007). This species has been recorded from the Black Warrior and Tallapoosa river drainages of the Mobile Basin, including Yates Reservoir, Bear Creek on Pickwick Lake, and the central part of the state of Alabama (Mettee et al. 1996; Rasmussen 1998; Hornsby and Pierson, personal communication; Mississippi Museum of Natural Science 2004). This species has been recorded from Arizona in Tucson for the first time in 2007 (L. Riley, pers. comm.). Early records from the 1970s may have been misidentified as bigheads but were most likely Bighead x Grass carp hybrids (P. Marsh, pers. comm.). In Arkansas, it has been taken from the Arkansas River just upstream of Pine Bluff, the lower Arkansas River between Dam #2 and the Mississippi River (Rasmussen 1998; J. Phillips, personal communication); has been stocked in several municipal sewage lagoons in the state (Robison and Buchanan 1988; Courtenay et al. 1991), and is established in White River National Wildlife Refuge (USFWS 2005). In California, in 1992, 26 specimens were taken from one of three ponds in a small drainage adjacent to Brannin Creek, Tehama County, in the Sacramento River basin (Dill and Cordone 1997). Bighead carp also has been stocked in water treatment ponds in Larimer County, Colorado (Horak, personal communication; P. Walker, personal communication), and two individuals were caught from Cherry Creek Reservoir in Denver in 2004 and stocked in Birdland Reservoir in Metro Denver by the Bureau of Reclamation (P. Walker, personal communication). This species has been recorded from Florida (Shafland 1996) including Lake Okeechobee (D. Fox, personal communication). A single specimen was taken in August 1994 from St. Andrews Bay at the Deer Point Lake spillway, Bay County, Florida (Middlemas 1994; UF 98162). Another was taken from a lake on the southeast side of Lake Okeechobee, Florida (FMNH).  Bighead Carp were collected from several water bodies in, or bordering, Illinois, including the Mississippi and Ohio rivers and several of their tributaries, the Cache, Big Muddy, and Kaskaskia river drainages, and Horseshoe Lake in Madison County (Burr 1991; Burr et al. 1996; Tucker et al. 1996; Ross 2001; Rasmussen 1998), the Illinois River (K. Cummings, personal communication; USFWS 2005), and Chain Lake, Schuyler County, Illinois (Jennings 1988). Bighead Carp were collected in Bryant Creek, Oxendine Bayou, Vigo County, Indiana (Illinois Natural History Survey 2004), the Ohio River at mile marker 919 on the Indiana-Kentucky border (Freeze and Henderson 1982; D. Jennings 1988); the Chariton River below Rathbun Lake, Desoto National Wildlife Refuge (Located along the Missouri River, 25 miles north of Omaha), and the Des Moines River, in Iowa (J. Bruce, personal communication; USFWS 2005); the Kansas, Delaware, Neosho, Arkansas, Missouri, and Wakarusa rivers in Kansas (Cross and Collins 1995; Halker 1998; Rasmussen 1998); several waterbodies in Kentucky (Freeze and Henderson 1982; Jennings 1988; Southern Illinois University; Thomas, pers. comm; Henley, pers. comm.); several water bodies in Louisiana, including the Atchafalaya River, Red River drainage, and Turkey Creek (Carp Task Force 1989; Rasmussen 1998) and the Red-Ouachita River (Douglas et al. 1996); from Lake Pepin (Mississippi River) in Minnesota waters in October 2003 (S. DeLain, personal communication); from several water bodies in, or bordering, Missouri, including the Mississippi River mainstem, the Missouri, Chariton, Osage, and Salt rivers, among others (Bennett 1988; Robinson 1995; Tucker et al. 1996; Pflieger 1997; Rasmussen 1998; Southern Illinois University; Chapman, pers. comm.; Etnier, pers. comm.) collected in Brick House Slough [vicinity of Alton, IL] (Illinois Natural History Survey 2004); various water bodies in Mississippi, including the Yazoo and Pascagoula river drainages (Douglas et al. 1996; Ross 2001; Mississippi Museum of Natural Science 2004) and along the main channel of the Mississippi River of the state below a wing dike (L. Nico, personal communication); the Missouri River area and Platte River of Nebraska (Howells 1990; Rasmussen 1998; Nebraska Game and Parks 2000) established in Boyer Chute National Wildlife Refuge (USFWS 2005); Lake Erie, Ohio, off Cedar Point (T. Cavender, personal communication); several sites in the Grand River drainage of Oklahoma, including the Neosho River in Ottawa County, Grand River in Mayes County, upper Grand Lake, and Lake Hudson (Pigg et al. 1993, 1997; Rasmussen 1998);  the Missouri River up to Gavins Point Dam in South Dakota (Rasmussen 1998; W. Stancill, personal communication); the Mississippi River mainstem, the Hatchie River, Guntersville Lake, and the Tennessee River near Lake Barkley, Tennessee (Etnier and Starnes 1993; Anonymous 1995; Simms 2005); Victor Braunig, Kirby, and Fort Phantom Hill Reservoirs and Red River below Lake Texoma in Texas (Howells 1992; Rasmussen 1998; Texas Parks and Wildlife 1999; Texas Parks and Wildlife Department 2001); collected near I-81 in Washington County, Virginia (W. Kittrell, personal communication); and the Ohio River at Moundsville, West Virginia (M. Hoeft, personal communication).

The morphology of the Bighead Carp’s comb-like gill rakers and epibranchial organ allow this species to have a broad and flexible diet. This species is more efficient at filtering larger prey items like zooplankton and large phytoplankton, however in times of zooplankton scarcity Bighead Carp are capable of ingesting particles up to four times smaller than gill raker width (Opusyznski and Shireman 1991). Bighead Carp are also capable of consuming detritus, which in some cases has made up the dominant portion of their diet (Anderson et al. 2016; Boros et al. 2014; Calkins et al. 2012; Kolar et al. 2007). 

Female Bighead Carp reach sexual maturity at three years of age, while males can reach sexual maturity in two years; however, this varies significantly with changing environmental conditions (Huet 1970; Kolar et al. 2007). Bigheaded carps are only known to spawn in large, turbulent rivers and it is believed that a rising hydrograph (flood event) is a primary spawning cue (Kolar et al. 2007). However, several studies have shown that rising water levels are not always necessary for spawning—indicating that these fish exhibit a phenotypic plasticity that may facilitate their successful establishment in novel ecosystems (Coulter et al. 2013; Kocovosky et al. 2012; Deters et al. 2012). Fecundity increases with age and body weight and is directly related to growth rate (Verigin et al. 1990). In its native range, Bighead Carp fecundity ranges from 280,000-1.1 million eggs. In North America, fecundity ranged from 4,792-1.6 million eggs (Kipp et al. 2011).  Bighead Carp produce eggs that are semi-buoyant and require current to keep them from sinking to the bottom (Soin and Sukhanova 1972; Pflieger 1997). The eggs float for 40-60 hours before hatching.

Bighead Carp can grow rapidly in productive environments. In the Mississippi River, Bighead Carp grew to 1 kg in weight by age 2 and up to 852 mm in length by age 3 (Nuevo et al. 2004).

The oldest Bighead Carp recorded in the United States was believed to be 8-10 years old, and maximum age in China was reported to be 16 years. However, there is a lack of specific information regarding the longevity of this species and it is possible that they can be quite long lived (Kolar et al. 2007).

The U.S. Army Corps of Engineers  constructed a set of three electrical barriers, the first of which opened in 2002, on the Chicago Sanitary and Shipping Canal to prevent the spread of aquatic invasive species between the Great Lakes and Mississippi River basins; only one live bighead carp has been found  (Lake Calumet in 2010) in the waterway above the barrier and a dead individual was found on the shore of Lake George, Indiana (Baerwaldt et al. 2013).

While not indicative of live fish, environmental DNA (eDNA) of bighead carp was been found in water samples collected above the electric barriers (i.e., closer to Lake Michigan) in 2012 from Lake Calumet (USACE 2012).  Additional eDNA of silver carp has been found in Sandusky Bay, Lake Erie (OH) (MI DNR 2012).

As of 2012, there were no bigheaded carps in or near the St. Lawrence River and opportunities for the introduction of bigheaded carps to the St. Lawrence River are not well understood.  However, should they gain access to the St. Lawrence River, laker ballast water or natural dispersal would provide a direct route to Lake Ontario  (Cudmore et al. 2012).

The potential for purposeful, human-mediated releases of bigheaded carps into the Great Lakes basin does exist. Humans have illegally released freshwater fishes for sport opportunities (Crossman and Cudmore 1999a, Bradford et al. 2008) or spiritual/ethical reasons (Crossman and Cudmore 1999b, Severinghaus and Chi 1999, Shiu and Stokes 2008). This human behavior of illegally releasing nonnative fishes into the aquatic environment is difficult to characterize and quantify (Bradford et al. 2008).

Most states prohibit the use of carp as baitfish, however juvenile carp may be present as a contaminant in baitfish.  Feeder fishes (typically Goldfish (Carassius auratus) or “rosy reds” (colour variant of Fathead Minnow (Pimephales promelas)) shipped into the Great Lakes basin could be contaminated with bigheaded carps if they originated from fish farms in the Mississippi River basin. Fathead Minnows found in the bait industry in Michigan are known to originate from culture in Arkansas, Minnesota, North Dakota, and South Dakota (G Whelan, Michigan DNR, pers. comm.). However, the volume of such movement and the extent of contamination, if any, is unknown. Based on a subsample of live fish import records for 2006-2007, fathead Minnows (likely rosy reds) imported for the aquarium trade originated primarily from Missouri and secondarily from North Carolina (Cudmore et al. 2012). 

It is currently illegal to possess or sell live Invasive Carps in Ontario; however, despite this legislation, bighead carp and grass carp were documented in shipments for import into Ontario. Eight entry records were recorded from January 2010 to August 2011 that listed grass (9.8 mt) and bighead (16.8 mt) carps as species descriptions. All of the shipments originated in Arkansas.” (Cudmore et al. 2012)
There are many ponds and artificial lakes in the Chicago metropolitan area which are commonly stocked for fishing with Channel catfish (Ictalurus punctatus). Channel catfish are often purchased from southern fish farmers, where it is possible for the stock to be contaminated with juvenile bighead carp. For instance, in September 2011, 17 large bighead carp were collected from Flatfoot Lake in the Beaubien Forest Preserve (K. Irons, Illinois Department of Natural Resources, pers. comm.).  Three bighead carp were also found from Schiller Pond.  Escapes of another Invasive Carp, grass carp, have occurred in similar circumstances.

Hypopthalmichthys nobilis has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

Bighead carp have been able to establish themselves in a wide range of environments with a wide range of temperatures and lower salinity levels. They are moderately dietary generalists feeding on a variety of zooplankton and algae (Gollasch et al 2008).  Bighead carp have been demonstrated to outcompete both native larval fishes and mussels (Laird and Page 1996).  It would be highly likely for the bighead carp to find an appropriate food source but the amount they eat might not be sufficiently found in the Great Lakes. Recent bioenergetics models suggest that productive nearshore areas and embayments (e.g. Green Bay and the Western Basin of Lake Erie) would be able to sustain growth of Bighead and Silver carp, but these species would likely be food-limited in the oligotrophic offshore regions (Anderson et al. 2017;  Anderson et al. 2015; Cooke and Hill 2010).

Their locations in Asia suggest their ability to withstand the Great Lakes waters during the winter period.  Winter mortality is not known to be an issue for bigheaded carps in the Mississippi River basin; bigheaded carp fingerlings are collected from floodplain wetlands in the spring in years when those wetlands were not connected to the river (D. Chapman, USGS, pers. obs.). Overwinter mortality may influence the northern limits of the native range of bigheaded carps, but has not been modelled specifically for these species in North America.   Ecological niche modeling predicting the potential North American distribution of bigheaded carps indicated that they could survive well north of the Great Lakes basin (Herborg et al. 2007); therefore, overwinter mortality will likely not be a limiting factor in most years (Cudmore et al. 2012

Kolar et al. (2007) stated that the limiting factor for Invasive Carp establishment in most regions of United States would be access to a river in which Invasive Carp could successfully spawn. Bighead carp need large, turbulent rivers and higher temperatures to spawn. The eggs float for 40-60 hours before hatching. Only some rivers emptying into the Great Lakes are sufficient of this characteristic and at only parts of the year. Two studies have examined the suitability of Great Lakes tributaries for bigheaded carp spawning based on more detailed considerations of reproductive biology. Kocovsky et al. (2012) examined eight American tributaries in the central and western basins of Lake Erie. They considered: the thermal conditions of the tributaries and Lake Erie, the minimum total degree-days required for maturation, onset of spawning and mass spawning, timing of flood events as triggers for spawning, and length of stream required for egg hatching based on stream velocity and estimated incubation time. They concluded that the three larger tributaries were thermally and hydrologically suitable to support spawning of bigheaded carps, four tributaries were less suited, and that one was ill suited. Mandrak et al. (2011) conducted a similar analysis for the 25 Canadian tributaries of the Great Lakes. They concluded suitable spawning conditions were present in nine of 14 tributaries to Lake Superior with sufficient data; however, only one of the nine tributaries had a mean annual total degree-days exceeding 2,685. Therefore, bigheaded carps are unlikely to mature within Lake Superior tributaries, but may encounter sufficient growing degree-days to mature in some parts of Lake Superior such as near shore and bays. Further analysis is required to identify such areas. Mandrak et al. concluded suitable spawning conditions, including growing degree-days required for maturation, were present in 23 of 27 tributaries to Lake Huron, nine of 10 tributaries to Lake Erie, and 16 of 28 tributaries to Lake Ontario. These analyses suggest that access to tributaries with suitable thermal and hydrologic regimes in the Great Lakes should not limit spawning by bigheaded carps (Cudmore et al. 2012). Additionally, Cuddington et al. (2014) found that establishment would be likely for a small number of founding individuals (<20 fish) despite environmental stochasticity. Furthermore, the presence of only a few suitable spawning rivers on each lake may promote the establishment success given that the carp would have an increased chance of finding a mate in the relatively few nearby spawning rivers. However, establishment becomes less likely if age of first sexual reproduction is substantially delayed.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

Realized:
The spread of this species adversely affects commercial fishery in parts of the Mississippi River Basin (Maher 2005). Bighead carp has become a substantial portion of commercial catch, significantly outnumbering the catch of native species sought after commercially in several waters of the Midwest (Conover et al. 2007, Kolar et al. 2005). Commercial fishers on the Illinois River reported a 124% increase in the harvest of bighead and silver carps (reported together) and a 35% decrease in buffalo harvest during 2002. In the lower Missouri River, between 2002 and 2004, more than twice as many Hypophthalmichthys spp. were caught than all other commercial species combined. Furthermore, the average weight of individual Hypophthalmichthys spp. was estimated to be at least double that of the individual commercial species caught (Kolar et al. 2005). Unless economically viable markets develop, the establishment of large self-sustaining populations of bighead carp in the United States may compromise commercial fishing.

The diet of this species overlaps with that of planktivorous species (fish and invertebrates) and to some extent with that of the young of virtually all native fishes. If food resources become limiting, bighead carps may compete directly with these native species. The decline of native species that are important as sport and food species are bound to have a negative economic impact on recreational angling and other industries that benefit from sport fishing, such as tourism (Kolar et al. 2005).

Hypophthalmichthys nobilis has a high potential environmental impact in the Great Lakes.

Realized:
Bighead Carp are powerful filter-feeders with a wide food spectrum that grow fast and reproduce quickly (Xie and Chen 2001), which makes this species a strong competitor. Within its native China, Bighead Carp are considered invasive and are associated with declines in native planktivorous fishes when translocated outside their natural range (Li and Xie 2002). Xie and Chen (2001) found that stocking of Bighead Carp into the plateau lakes of China had disastrous effects on endemic fishes, especially filter-feeding, endemic Barbless Carp (Cyprinus pellegrini). The catch of Barbless Carp, that once represented 50% of yield of total fishes caught, declined to 20% in the 1960s, to 10% in the early 1970s, and plummeted to <1% in the 1980s.

The species also poses a threat to the ecology of the Mississippi River Basin and connecting aquatic ecosystems. These fish are capable of significantly reducing zooplankton abundance, which adversely affects all fish in their early life stages when their diets are strictly planktonic (Chick et al. 2001, Xie and Chen 2001). Furthermore, Bighead Carp compete with fish that are filter-feeders as adults, such as paddlefish. Several studies have showed that when zooplankton is limited, Bighead Carp have a competitive advantage over paddlefish, negatively affecting the relative growth of the latter (Schrank et al. 2003, Schrank and Guy 2003).

Furthermore, Bighead Carp is host to two pathogens that have the potential of affecting and native fish species. One of these parasites, the gill-damaging Lernaea cyprinacea, known as anchorworm, was found in Channel Catfish being cultured with Bighead Carp (Goodwin 1999). This parasite is also known to affect salmonids and eels. Anchorworm occurs worldwide, is known from 40 cyprinid species, and completes its life history on a single host (Hoole et al. 2001). Bighead Carp are also known to be host of Bothriocephalus acheilognathi, known as the Invasive Carp tapeworm. This cestode parasite, introduced into U.S. waters from Grass Carp, erodes mucus membranes and intestinal tissues, often leading to death of the host (Humpback Chub Ad Hoc Advisory Committee 2003). Yet, these adverse effects are minimal on Bighead Carp (Kolar et al. 2005). The Invasive Carp tapeworm is known to have infected native fishes of concern in five states: Arizona, Colorado, Nevada, New Mexico, and Utah. As the introduced range of Bighead and Silver carps grows in U.S. waters, a number of native fishes, particularly, but not limited to, cyprinids, percids, and centrarchids, will probably become hosts of the Invasive Carp tapeworm (Kolar et al. 2005).

Potential:

Bighead Carp have considerable effects on zooplankton communities. These fish are known to decrease the size of zooplankton within a species (Radke and Kahl 2002; Kim et al. 2003), possibly removing a species from the size category that would be consumed effectively by paddlefish. It seems likely that Hypophthalmichthys spp. have the potential to alter the food web in ways that could negatively affect fishes such as paddlefish that feed on large crustacean zooplankton (Kolar et al. 2005).

Hypophthalmichthys spp. also can alter species composition in phytoplankton communities by promoting the dominance of species that can resist digestion (Görgényi et al. 2016).

Food web models of Lake Ontario and Lake Erie have suggested that Invasive Carp impacts on the Great Lakes ecosystem might be mitigated by several factors and trophic interactions such as the availability of unused production that might be exploited by the carp, increased production at lower trophic levels due to high nutrients, and the potential for native piscivores to feed on larval Invasive Carp (Zhang et al. 2016; Currie et al. 2012).

Hypophthalmichthys nobilis has the potential for high beneficial effects if introduced to the Great Lakes.

Realized:
Bighead carp is a popular food fish in its native China and several other countries, ranking fourth in 1999 in world aquaculture production (FAO 1999). Although not so popular in North America, commercial fisheries for bighead carp exist on the Mississippi, Missouri, and Illinois rivers and are sold from small specialty food markets to consumers of various Asian cultures in major North American cities (Conover et al. 2007, Kolar et al. 2005, Stone et al. 2000). Nonetheless, the market for live bighead carp in the United States is limited (the typical consumer will buy only enough fish for the current day’s meal) and easily saturated. After bighead carp fry are produced by hatcheries and grown to market size by fish farmers, they are transported to live markets in Toronto, Chicago, New York, Boston, Montreal, and other cities (Conover et al. 2007).

Bighead carp are frequently used in polyculture with other fish, such as common carp, various tilapias, largemouth bass, and bigmouth buffalo (Jennings 1988) to control zooplankton and phytoplankton populations. In the United States, bighead carp are cultured in ponds with channel catfish and sometimes with grass carp to control macrophytes (Conover et al. 2007).

Additionally, bighead carp can be an important source of revenue for catfish farmers during times of low catfish prices (Stone et al. 2000).  Engle and Brown (1998) estimated that the net benefit of stocking bighead carp with catfish was substantially higher. Net benefits ranged from $1,628 to $2,743 annually from a 6-ha (15-acre) pond. Furthermore, there is evidence of bighead carp used as sport fish in Oklahoma. Relatively numerous sport fishing catches have been recorded downstream from a low-water dam in the Neosho River at Miami, Oklahoma (Jester et al. 1992).

Potential:
The role of bighead carp as a biological control agent for plankton control and removal is largely debated.  While Henderson (1978, 1983) suggested that both bighead and silver carps would stimulate phytoplankton blooms that would result in removal of nutrients by phytoplankton, Opuszynski (1980) found that organic carbon, nitrogen, and total phosphorous increased in bottom sediments, despite the decrease in nitrogen, phosphorous, and dissolved. When those bottom sediments were disturbed by activities of other fishes, phytoplankton populations increased. Furthermore, Lieberman (1996) stocked bighead and silver carps and found that total phosphorus and total inorganic nitrogen increased as a result. Yet, some studies have reported that bighead is able to improve water quality by continually removing plankton, especially blue-green algae. This stabilizes plankton and lessens the probability of die-offs in production ponds (Kolar et al. 2007, Schofield et al. 2005).

In the United States, Bighead Carp (as well as Silver Carp, Largescale Silver Carp, and Black Carp) are federally listed as injurious species under the Lacey Act (18 U.S.C. 42; 50 CFR 16). Therefore, it is illegal to import or to transport live specimens, including viable eggs or hybrids of the species, across state live, except by permit for zoological, educational, medical, or scientific purposes. Violation of the Lacey Act is a Class B misdemeanor, punishable by no more than six months in jail and/or up to a $5,000 fine for an individual, $10,000 for an organization.

Each Great Lakes state and province have regulations regarding Bighead Carp:

It is illegal to import, possess, deposit, release, transport, breed/grow, buy, sell, lease or trade Bighead Carp in Ontario (Invasive Species Act 2015). New York prohibits the possession, sale, importation, purchase, transport, or introduction of Bighead Carp. Intent to commit any of these actions is also prohibited (6 NYCRR Part 575). In Pennsylvania, it is illegal to transport, sell, offer for sale or release, or introduce Bighead Carp (Pennsylvania Consolidated Statutes Title 30 Section 2508). In Michigan, it is illegal to possess, import, sell, or offer to sell Bighead Carp (NREPA Part 413). Ohio lists Bighead Carp as an injurious aquatic invasive species and therefore it is unlawful for any person to possess, import, or sell live individuals within the state. Dead Bighead Carp can only be possessed in Ohio if they are preserved in ethanol or formaldehyde, or eviscerated (internal organs removed) (OH ADM. Code, 1501:31-18-01). Indiana prohibits the importation, possession, propagation, purchase, sale, barter, trade, transfer, loan, or release into public or private waters of live Bighead Carp or Bighead Carp eggs (312 IAC). Illinois lists Bighead Carp as an injurious species as defined by 50 CFR 16.11-15. Therefore, Bighead Carp cannot be possessed, propagated, bought, sold, bartered or offered to be bought, sold, bartered, transported, traded, transferred or loaned to any other person or institution unless a permit is first obtained from the Department of Natural Resources. Illinois also prohibits the release of any injurious species, including Bighead Carp (17 ILL. ADM. CODE, Chapter 1, Sec. 805). Wisconsin prohibits the transportation, possession, transfer of, and introduction of Bighead Carp (Wisconsin Chapter NR 40). Minnesota prohibits the possession, importation, purchase, sale, propagation, transportation, and introduction of Bighead Carp (Minnesota Rule 6216.0250).

Use of carp as bait is prohibited in all Great Lake states and the two Canadian provinces; with Michigan and Ontario specifically prohibiting the use of “Asian carps.” (Cudmore et al. 2012).  The Invasive Carp working group recommends development of certification program(s) for baitfish to be disease-free and uncontaminated by nonindigenous species (Conover et al 2007).

Control
The Aquatic Nuisance Species Task Force and the U.S. Fish and Wildlife Service organized an Invasive Carp Working Group (Working Group) to develop a comprehensive national Invasive Carp management and control plan. The Working Group agreed that the desired endpoint of the plan is the extirpation of Invasive Carps (bighead, silver, black and grass) in the wild, except for non-reproducing grass carp within planned locations (Conover et al 2007).

Monitoring of the Chicago Area Waterways System (including the Chicago Sanitary and Shipping Canal) supporting early detection allowing for rapid response is a key component of efforts to control the spread of Hypophthalmichthys nobilis from the Mississippi River system into the Great Lakes. 

Biological
Safe and effective biological control of bighead carp is not yet feasible.  Several potential technologies are being explored including: release of sterile male fish, triploid carp, transgenic alternatives (daughterless carp and Trojan genes), pheromones (sex lures or juvenile aggregation for traps), disease agents, parasites, predators.

Physical
Many types of physical barriers are being examined for potential to stop the dispersal of Invasive Carp including Hypophthalmichthys nobilis.  These include earth berms, fences, electric barriers, bubble curtains, acoustic barriers, strobe lights and high pressure sodium lights.  

The electrical fish barrier can function either as an impassable barricade or as a fish guidance system.   In either case, the system consists of a series of metal electrodes submersed in water to create an electrical field capable of repelling fish. Electrical barriers have been evaluated for preventing the expansion of feral Invasive Carp populations in both the Chicago Sanitary and Ship Canal and the Upper Mississippi River System. While considered feasible for the Chicago Sanitary and Ship Canal, it was determined that electrical barriers would be less effective and less feasible on the Upper Mississippi River System. The U.S. Army Corps of Engineers (USACE) constructed a set of three electrical barriers, the first of which opened in 2002, on the Chicago Sanitary and Shipping Canal to prevent the spread of aquatic invasive species between the Great Lakes and Mississippi River basins.  Although currently in use, electric barriers are not the end-all solution to the range expansion of feral Invasive Carps in the United States. Electric barriers are not selective as to species affected.

The bubble curtain is the most elementary form of behavioral fish barrier,  which in its simplest form consists of a perforated tube laid across a river bed through which compressed air is forced. The rising curtain forms a wall of bubbles that can deflect fish.   Efficacy of the bubble curtain may be enhanced when combined with light or sound. Acoustic barriers have shown promise in research trials. Bighead and silver carps have acute hearing and are sensitive to frequencies outside the range of many native species. Thus, an acoustic array could be designed such that it primarily affects bighead and silver carps and has less effect on non-target species.  The Invasive Carp working group recommends development of redundant barrier systems within the Chicago Sanitary and Ship Canal, including acoustic bubble curtains (Conover et al 2007).

In addition to the Chicago Sanitary and Ship Canal, the Great Lakes Regional Collaboration Aquatic Invasives Species Strategy Team Action Plan (USEPA 2005) identifies the Ohio canals and waterways system as priority interbasin connections that must be addressed to prevent the spread of Invasive Carps into the Great Lakes. Particular attention should be directed to the Ohio and Erie and Miami and Erie canals. The potential for spread of  Invasive Carps from the Ohio River Basin into the Great Lakes via these routes is significant (Conover et al 2007).  The Great Lakes and Mississippi River Interbasin Study (USACE 2014) includes site-specific analysis for 18 of these other aquatic pathways for dispersal between the two basins and makes specific recommendations for each.

High pressure sodium lights (1,000 watts) have been used to attract and hold fish to slow water areas located near a powerhouse spillway.   Mercury lights have also been used as attractants for species-specific applications. Attractants may be used in combination to congregate fish that are avoiding other behavioral barriers or deterrents.  The strobe light has been extensively evaluated as a fish deterrent in both laboratory and field situations and has been used in conjunction with other behavioral devices to increase the level of fish diversion. Combinations with bubble curtains may enhance the  effectiveness of both, as the light can be projected onto the bubble sheet. Strobe lights can repel fish by producing an avoidance response.

Increasing the commercial and recreational harvest of Invasive Carps in the Mississippi River basin is an important component of the strategy for preventing the spread of these fishes to the Great Lakes.  Reducing population size, particularly in waterways near the Great Lakes, reduces propagule pressure.  The effects of Invasive Carps on native ecosystems are likely to be proportional to their abundance, thus reducing population size can also be an important component of efforts to minimize impact (Conover et al 2007).

Chemical
The toxicity of many chemicals to bighead, grass, and silver carps has been examined (13 chemicals, 34 studies for bighead carp; 75 chemicals, 233 studies for grass carp; 21 chemicals, 83 studies for silver carp; Pesticide Action Network 2005).  Rotenone and antimycin are the only registered piscicides available to potentially control Invasive Carps in the United States without considerable additional expense. Rotenone and antimycin are both labeled for use in lakes and running waters (i.e., streams and rivers). The American Fisheries Society has published a manual for the use of rotenone in fisheries management (Finlayson et al. 2000). Research is needed to further investigate the effectiveness of registered piscicides to control Invasive Carps, evaluate their potential use in the control of feral populations, and to determine the potential of other chemicals to control Invasive Carps.

Other
The Invasive Carp Working Group recommends development of a decision support system to prioritize locations for barriers to carp dispersal.

Voucher specimens: Florida (UF 98162).