asian carps

Silver, bighead, and grass carps are all invasive fishes (along with several other carp species) that originally came from large rivers in Asia and so are often referred to as "Asian carp." The closest reproducing population of silver and bighead carps to date is thought to be in Iowa, and both species now threaten to become established in Minnesota, where approximately 30 silver and bighead carp combined have been caught between 1996 and the end of 2015. Asian carps pose threats to aquatic vegetation, food webs, commercial and recreational fishing, and silver carp pose an extra threat to human health due to their propensity to leap out of the water when disturbed by watercraft.

Current research at MAISRC focuses on detection using optimized eDNA and microbial techniques, prevention using enhanced bubble curtains and modifications to locks and dams, control using Judas fish techniques and attractants, and possible eradication using native pathogens. Efforts also include a risk analysis to guide Asian carp management decision-making. Click here to download a factsheet about Asian carp research at MAISRC.

About Asian carp

What they are 

Grass carp were originally introduced to the United States in 1963 as a method for pond and lake maintenance (Mitchell and Kelly 2006) and are still stocked and sold in some states. Due to concerns about its invasiveness, grass carp are commonly produced as triploid, or sterile, fish. Illegal sale and transport of diploid fish can still result in unwanted fertile populations. The ecological risk associated with grass carp has been uncertain, however recent observations of wild grass carp in the Great Lakes basin have caused some environmental managers to call for the re-evaluation of the ecological risk and regulatory structure concerning this species (e.g., Conover et al. 2007).

Bighead and silver carp were imported to the U.S. in the 1970s and escaped from captivity shortly thereafter. Silver and bighead carps have become highly invasive in rivers such as the Mississippi and Illinois Rivers, where they can comprise up to 75% of the fish biomass (Kolar et al. 2005). Bighead and silver carp are considered a threat to native aquatic biodiversity and ecosystem health because of their wide environmental tolerances, large size, high fecundity, and voracious filter-feeding eating habits. Additionally, silver carp, with their tendency to jump up to 3 meters out of the water when disturbed (Kolar et al. 2005) can threaten human safety, recreation, and water-based economies.

The closest reproducing population of silver and bighead carps to date is thought to be in Iowa, and both species now threaten to become established in Minnesota, where approximately 30 silver and bighead carp combined have been caught between 1996 and the end of 2015. The location and abundance of bighead and silver carp in Minnesota has proven difficult to determine. Weaknesses that may be targeted for detection, prevention, and control include: a tendency for these fish to aggregate and shoal (Sorensen and Ghosal); their unique olfactory and eating habits; their swimming capabilities; and their exceptionally good sense of hearing as compared to many other native fish.

Life cycle

Bighead carp (Hypophthalmichthys nobilis) mature at 2-7 years old. Adults spawn in rivers, and their eggs drift into low-flow nursery areas. Each female can produce up to one million eggs per year. Both juveniles and adults eat zooplankton, the basis of the food chain.

Silver carp (Hypophthalmichthys molitrix) mature at 2-6 years old and have similar spawning habits to bighead carp. Females can produce up to two million eggs per year. Juveniles eat zooplankton and phytoplankton; adults just eat phytoplankton.

Grass carp (Ctenopharyngodon idella) mature at 4-7 years old, with females producing up to two million eggs per year. Juveniles prey on aquatic invertebrates; adults eat aquatic and terrestrial plants.

What they affect

Grass carp are voracious feeders that pose a threat to terrestrial plants, such as shrubs at the water line. Grass carp can also eradicate aquatic vegetation that serves as a food supply for waterfowl and as refuge from predators for young fishes (Bain 1993). Even in areas where they have become established – the Chicago canal system, for example – grass carp do not appear to become a dominant component of fish biomass.

Silver and bighead carps are filter-feeders, straining microscopic plants and animals out of the water and away from paddlefish, gizzard shad, and young gamefish which rely on them. This disruption affects native fish and waterfowl and could result in diminished recreational and commercial fishing opportunities in the region. Silver carp also pose a threat to human health due to their propensity to leap out of the water when disturbed by watercraft.

Where they're found

Populations of bighead and silver carps are established in the Mississippi River and its tributaries downstream of pool 16, near Davenport, Iowa. In Minnesota, individual Asian carps have been caught, but there is no evidence to date that they are reproducing in Minnesota waters.

  • Fifteen individual bighead carp have been caught in the St. Croix River since 1996, with five caught in June of 2015 near Stillwater – the furthest upstream the invasive fish have been detected and the largest number caught in the St. Croix to date.
  • Ten silver carp have been caught in the Mississippi River in Minnesota since 2008, as far upriver as Pool 2, near Cottage Grove, in 2014.
  • Numerous individual grass carp have been caught in Minnesota, including in the Mississippi River and the St. Croix River. Many are thought to be escapees from stocking operations in Iowa, which allows for the sale of sterile grass carp, however a diploid (sterile) grass carp was caught in the Minnesota River in December of 2015. The invasion front for grass carp is currently thought to be the Great Lakes, where grass carp populations have recently been found and are expected to expand (Kocovsky et al. 2012; Chapman et al. 2013; Cuddington et al. 2014).

How they spread

Grass carp were introduced to the U.S. in the early 1960s and subsequent intentional and accidental releases have led to their becoming established in many states (Guillory and Gassaway 1978; Hargrave and Gido 2004).

Bighead and silver carps were imported to the southern U.S. in the 1970s to remove algae and other suspended matter out of catfish farm ponds and wastewater treatment plants. They escaped into local waterways shortly afterwards following severe flooding in which farm ponds overflowed their banks. Since then, they have been traveling steadily upstream, spreading to major river systems, including the Mississippi River, toward Minnesota.

Bighead carp thrive in degraded and channelized river environments, making the Chicago River and the Mississippi River ideal pathways of spread. Researchers at the MAISRC believe an impediment to the northward invasion of bighead and silver carps is the lock and dam system maintained by the US Army Corp of Engineers, which could be optimized to block their spread.

What they look like

bigheadBighead carp can be up to 1.3 meters (51 inches) in length, weigh up to 110 pounds (50kg), and live at least 9 years. They are silver in color with dark blotches along the dorsal region, and have no scales on their heads.

asian carpSilver carp can be up to 1 meter (39 inches) in length, weigh up to 77 pounds, and live up to 20 years. They are also silver with no scales on their head, and with a downward slanting mouth.


grassGrass carp can be up to 1.5 meters (59 inches) in length, weigh up to 99 pounds, and can live up to 21 years. They are olive green in color with a rounded snout and an over-hanging upper lip.


All carps in the genus Hypophthalmichthys can be characterized by a stout body with a large head, downward-facing eyes, small scales, and a jaw without teeth. Two defining features of the genus are gill rakers and epibranchial organs, which sense chemical food cues and may control reflexive filter feeding behavior in bighead carp. It has been established that filter function is a passive and mechanical morphological function, meaning that chemosensory perception is important for these fish to feed – as opposed to vision – opening up a potential opportunity for control. In addition to their unique epibranchial organs, carp also have an above-average sensitivity to sound. They detect sound with much greater sensitivity than most native fish – another life history weakness that may be targeted for control.

Asian carp research at MAISRC


Completed efforts

  • Using common carp as a model, the Sorensen Lab has developed a valid and reliable qPCR assay marker and used it to determine optimal eDNA sampling and extraction procedures and available eDNA extraction kits

  • The Sorensen Lab has determined that eDNA does not persist across large expanses of natural waters, calling to attention a new, critical need to sample waters in an extremely strategic manner

  • The Sorensen Lab has identified a number of bacteria specific to silver, bighead, and common carps that have potential to be developed into testable bacterial source-tracking markers that could be used to determine the presence of these fishes

  • The Sorensen Lab has conclusively demonstrated that juvenile silver and bighead carps shoal (aggregate) in the laboratory, meaning that the Judas fish concept has potential to be used to locate and control these species

  • Masculinization of carps using steroid implants has been characterized by the Sorensen Lab and appears to be a viable technology for use with Judas fish

  • The Sorensen Lab has shown that olfaction drives feeding responses in bighead and silver carps and that the epibranchial organ functions as a pharyngeal taste organ

  • Laboratory experiments by the Sorensen Lab have shown that food attractants have the potential to be used for control of bighead and silver carps; experiments using juvenile bighead and silver carp have demonstrated that ingestion behavior (buccal pumping) in both species is largely mediated by food-related chemicals and can be stimulated with highly filtered food extracts

  • The Sorensen Lab has been able to demonstrate that silver and bighead carps are strongly repelled by sound in a highly directional manner that is associated with local acoustic particle motion

  • The Sorensen Lab has shown that the simple and inexpensive technology of an enhanced bubble curtain can, on its own, deflect nearly 90% of both bighead and silver carps from entering experimental channels in the laboratory

  • The Phelps Lab has identified two novel viruses from common carp and grass carp mortality events: novel picornavirus and novel paramyxovirus

  • The Phelps Lab identified the first report of Grass Carp Reovirus (GCRV) associated with fish mortality in the United States.

  • The Andow Lab has completed the first step in a risk assessment, which identified a list of potential adverse effects that could result from the establishment of Asian carp in Minnesota

  • Through interviews and focus groups with a diverse set of agency officials and stakeholders, the Andow Lab identified the primary tensions and conflicts in Asian carp management in Minnesota  

Current projects

Completed projects

Related news