Leuciscus molitrix Valenciennes, 1844  

Silver carp are unlikely to be confused with native cyprinids due to size and unusual position of the eye. They are most similar to bighead carp (H. nobilis) but have a smaller head, and upturned mouth without teeth, a keel that extends forward past pelvic fin base, lack the dark blotches characteristic of bighead carp and have highly branched gill rakers.

Juvenile fish lack spines in fins.  Metalarvae and early juvenile are similar to bighead carp (Hypophthalmichthys nobilis) but pectoral fin extends only to base of pelvic fin (as opposed to beyond in the pelvic fin in bighead)

The species is known for leaping out of the water when startled (e.g., by noises such as a boat motor).

Distinguishing characteristics were given in Berg (1949). Keys that include this species and photographs or illustrations are provided in several of the more recently published state and regional fish books (e.g., Robison and Buchanan 1988; Etnier and Starnes 1993; Pflieger 1997).

In their native range, silver carp reach maturity at between 4 and 8 years old but are noted in North America to mature as early as just 2 years old.  They can live to 20 years.  Spawning occurs at temperatures greater than 18oC.  A mature female can lay up to 5 million eggs per year.  Eggs require current to stay suspended, with a minimum length of spawning river estimated at 100km and a current speed of 70cm/s.

Hypophthalmichthys molitrix has a moderate probability of introduction to the Great Lakes (Confidence level: High).

Potential pathway(s) of introduction: Dispersal, unauthorized release, escape from commercial culture
Currently, large populations of this species are already established in nearby waters connected to the Great Lakes basin including the Illinois river and the Chicago Area Waterway System (Baerwaldt et al. 2013). On June 22nd, 2017 a 4 year old male silver carp was found nine miles from Lake Michigan in the Little Calumet River of the Chicago Area Waterway System (CAWS). This was the first silver carp collected above the electrical barriers in the CAWS. The autopsy revealed that this fish originated in the Illinois/Middle Mississippi watershed and spent a quarter of its life in the Des Plaines River watershed before being caught and removed from the Little Calumet River. Though it remains unknown how the fish arrived above the electric barriers, the autopsy revealed that the fish spent anywhere from a few weeks to a few months in the stretch of river where it was collected (Asian Carp Regional Coordinating Committee 2017). Prior to this record, the closest location to Lake Michigan at which a silver carp has been collected was in the Des Plaines River (river mile 290.2) at the confluence with the CSSC, north of Joliet, IL and downstream of the electric barriers (USGS 2013).

Live silver carp are sometimes available in live food fish markets in several major U.S. and Canadian cities, including Toronto (Kolar et al. 2005).

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

The silver carp has unique, sponge-like and porous gill rakers capable of straining phytoplankton down to 4 microns in diameter (Robison and Buchanan 1988). They can feed in temperatures as low as 2.5°C (36.5°F) and can withstand low levels of oxygen (Pennsylvania Sea Grant 2013). It would be highly likely for the silver carp to find an appropriate food source but the amount they eat might not be sufficiently found in the Great Lakes. Recent bioenergetics modeling efforts suggest that plankton concentrations could support silver carp growth in productive nearshore areas and embayments (e.g. Green Bay and the Western Basin of Lake Erie), but the fish would likely be food-limited in the oligotrophic offshore regions (Cooke and Hill 2010; Anderson et al. 2015; Anderson et al. 2017).

Kolar et al. (2007) stated that the limiting factor for invasive carp establishment in most regions of the United States would be access to a river in which invasive carp could successfully spawn. Several studies have found that there are several Great Lakes tributaries that have the necessary hydrologic characteristics and temperature regimes to support successful spawning (Kocovosky et al. 2012; Murphy and Jackson 2013; Chapman et al. 2013). Additionally, Cuddington et al. (2014) suggests 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 silver carp would have an increased chance of finding a mate due to the fish aggregating 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

Silver carp are carriers of disease-causing agents, posing health risks to humans, particularly in different parts of Iran. These pathogens include Listeria monocytogenes (found in market and fish farm samples), Clostridium botulinum (present in 1.1% of fresh and smoked samples from the Mazandaran Province), and toxigenic fungi such as Aspergillus flavus, Alternaria, Penicillium, and Fusarium (detected in silver carp and the pond water where they were raised). Additionally, silver carp may serve as a potential carrier of Salmonella (S. typhimumium) (USFWS, 2006).

These fish compete with native species that are important as sport and food species and whose decline could result in a negative economic impact on recreational angling and other industries that benefit from sport fishing, such as tourism (Kolar et al. 2005).

Hypophthalmichthys molitrix has a high potential environmental impact in the Great Lakes.
The silver carp is a filter-feeder capable of consuming large amounts of phytoplankton, zooplankton, bacteria, and detritus (Leventer 1987). Silver carp, as efficient filter feeders, engage in interspecific competition with various fish species during their early life stages, potentially leading to declines in the physical condition and long-term sustainability of native fish when plankton resources are limited (Chick and Pegg, 2001; Irons et al., 2007). Studies indicate that their superior filter efficiency and large size can disproportionately deplete plankton, alter zooplankton communities, and modify food web structure (Domaizon and Devaux, 1999; Spataru and Gophen, 1985; Starling, 1993; Irons et al., 2007; Pongruktham et al., 2010). Furthermore, Silver carp can impact water quality by excreting substantial amounts of nutrients, leading to increases in inorganic nitrogen and phosphorus levels, changes in zooplankton populations, and subsequent increases in chlorophyll a and turbidity (Herodek et al., Starling, 1993; Lieberman, 1996).

Another concern is the presence of the Asian tapeworm, which has been found in silver carp populations and poses a risk of transmission to other fish species, causing severe intestinal damage (Kolar et al., 2007; Conover et al., 2007). This parasite has also been detected in several native North American fish species, including endangered species (Kolar et al., 2005).

Hypophthalmichthys molitrix has the potential for high beneficial effects if introduced to the Great Lakes.
Silver carp holds significant commercial value worldwide, with China being a particularly important producer. In the US, commercial harvest of silver carp is increasing in certain regions of the Mississippi River Basin, and there is ongoing investigation into developing a consumer market for invasive carp species, along with the emergence of fishing tournaments targeting silver carp (Kolar, 2005; Conover et al., 2007). These fish are often studied for biomanipulation purposes in wastewater treatment and eutrophic lakes, but conflicting results have been observed regarding their effectiveness in controlling plankton blooms and improving water quality (Domaizon and Devaux, 1999b; Henderson, 1978; Spataru and Gophen, 1985; Starling, 1993). Similarly, debates persist about the ability of silver carp to control cyanobacteria blooms, with some studies suggesting their consumption of blue-green algae while others indicate potential increases in blue-green algae and overall phytoplankton populations (Xie et al., 2004; Kolar et al., 2005).

The report in Fuller et al. (1999) from Bay County, Florida was actually a bighead carp (UF 98162).

Voucher specimens: Illinois (SIUC 17716, 23043, 23046, 24415; INHS 88425); Louisiana (NLU 65811, 66858, 66859).