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Grass Carp - Ctenopharyngodon idella

Aquatic Invasive Species
Non-native Species
Not Documented

Global Rank: G5
State Rank: SNA
(see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
A conservation status rank is not applicable because this species is not a suitable target for conservation activities as a result of being exotic or introduced.
General Description
Grass Carp is a large member of the minnow family with a body which is moderately compressed laterally. Its mouth is terminally located on a wide head and eyes are small and low on the head. It lacks barbels. It is olive-brown on the dorsal side, with silver sides and a white belly. Scales are large with dark edging. The dorsal fin origin is anterior to the pelvic fin origin and it has a short caudal peduncle. It differs from goldfish (Carassius auratus) and common carp (Cyprinus carpio) in having a terminal mouth, shorter dorsal fin (only 7-8 rays) and from Hypophthalmichthys species (Bighead and Silver carps) in having fewer anal rays (9 or fewer) and fewer but larger lateral scales.

Diagnostic Characteristics
It differs from goldfish (Carassius auratus) and common carp (Cyprinus carpio) in having in having a terminal mouth instead of a sucker-mouth, a shorter dorsal fin (only 7-8 rays) and from Hypophthalmichthys species (Bighead and Silver carps) in having fewer anal rays (9 or fewer) and fewer but larger lateral scales.

Range Comments
Native Range: Eastern Asia from the Amur River of eastern Russia and China south to West River of southern China (Lee et al. 1980 et seq.; Shireman and Smith 1983).

Introduced Range: Grass Carp have been recorded from 45 states; there are no reports of introductions in Alaska, Maine, Montana, Rhode Island, and Vermont. It is known to have established populations in a number of states in the Mississippi River basin. Breeding populations have been recorded for the Mississippi River in Kentucky (Conner et al. 1980; Burr and Warren 1986), the Illinois and upper Mississippi rivers of Illinois and Missouri (Raibley et al. 1995), the lower Missouri River in Missouri (Raibley et al. 1995), the Mississippi River or its tributaries in the states of Arkansas (Conner et al. 1980), Louisiana (Conner et al. 1980; Zimpfer et al. 1987), Tennessee (Etnier and Starnes 1993), and presumably Mississippi (Courtenay et al. 1991). It is also established in the Ohio River in Illinois (Burr, personal communication); it was listed as established in Minnesota (Courtenay et al. 1991, but see Courtenay 1993), and in the Trinity River of Texas (Waldrip 1992; Webb et al. 1994; Elder and Murphy 1997). Courtenay (1993) listed Grass Carp as established in eight states, Arkansas, Kentucky, Illinois, Louisiana, Missouri, Mississippi, Tennessee, and Texas; an additional one, Minnesota, was included in an earlier listing of states with established populations (Courtenay et al. 1991). Stone (1995) listed this species as being established in Wyoming.

None have been detected in Montana. The closest potential invasion location is in the Loch Leven (detected in 2000), in Cypress Hills Provincial Park, Saskatchewan, Canada. This is within the Frenchman River Watershed (10050013) which is a tributary to the Milk River.

For maps and other distributional information on non-native species see:
Nonindigenous Aquatic Species Database from the U.S. Geological Survey
Invasive Species Habitat Tool (INHABIT) from the U.S. Geological Survey
Invasive Species Compendium from the Centre for Agriculture and Bioscience International (CABI)
EDDMapS Species Information EDDMapS Species Information

Grass carp individuals generally do not travel long distances except for the annual spawning migration (Mitzner 1978; Nixon and Miller 1978; Bain et al. 1990). Nevertheless, there are reports of juvenile Grass Carp traveling as far as 1,000 km from their original spawning grounds (Stanley et al. 1978).

Typical habitat includes quiet waters, such as lakes, ponds, pools, and backwaters of large rivers. Shallow water is the generally preferred habitat, although deeper waters are used when temperatures decrease (Nixon and Miller 1978).

Food Habits
Grass carp are herbivorous and focus on eating aquatic plants and the algae associated with them. A single Grass Carp can digest only about half of the approximately 4.5 kg of plant material that it consumes each day. The remaining material is expelled into the water, enriching it and promoting algal blooms (Rose 1972).

In their overview, Chilton and Muoneke (1992) reported that Grass Carp seem to affect other animal species by modifying preferred habitat, an indirect effect. However, they also indicated that grass carp may directly influence other animals through either predation or competition when plant food is scarce. In his review, Bain (1993) stated that Grass Carp have significantly altered the food web and trophic structure of aquatic systems by inducing changes in plant, invertebrate, and fish communities.

Oxygen consumption (per gram of body mass) increases with higher water temperature and decreases with fish age and mass (Chen and Shih 1955; Wozniewski and Opuszynski 1988). The lethal low oxygen level for juveniles was <0.5 mg/L (Negonovskaya and Rudenko 1974). The maximum pH for culture of grass carp was reported as 9.24 (Liang and Wang 1993). Egg hatching was delayed below pH 6.5 and increased mortality and deformation of larvae occurred below pH 6.0 (Li and Zhang 1992). Sensitivity to low pH decreased with age (Li and Zhang 1992). Median lethal concentration of ammonia was determined to be 1.05 mg/L (Gulyas and Fleit 1990).

Reproductive Characteristics
Egg production and fertilization take place when water temperatures are above 12°C in the spring and the release rate is maximized over 17°C ( ).

Probably the single most important management tool to preventing unwanted grass carp introductions in Montana's waterbodies is limiting any unregulated stocking and preventing the transportation of live fish in live wells between waterbodies.

Contact information for Aquatic Invasive Species personnel:
Montana Fish, Wildlife, and Parks Aquatic Invasive Species staff
Montana Department of Natural Resources and Conservation's Aquatic Invasive Species Grant Program
Montana Invasive Species Council (MISC)
Upper Columbia Conservation Commission (UC3)

Threats or Limiting Factors
Grass Carp appears to be tolerant of low levels of salinity, and may occasionally enter brackish-water areas. Fry (32-50 mm TL) survived transfer from freshwater to a salinity of 12 ppt (Chervinski 1977). Adults (2+ years) survived 10.5 ppt salinity for about 24 days and 17.5 ppt for 5 hours (Cross 1970). However, Grass Carp acclimated to 3, 5, and 7 ppt had an upper tolerance of about 14 ppt (Kilambi and Zdinak 1980). Maceina and Shireman (1980) showed that fingerlings reduce feeding at 9 ppt and stop feeding altogether at 12 ppt; thus, they predicted Grass Carp could inhabit brackish water bodies up to 9 ppt. Maceina and Shireman (1979) reported that the species can tolerate 14 ppt for as long as 4 days, but that the upper long-term tolerance of fingerlings to saline waters was lower, about 10-14 ppt. Maceina et al. (1980) noted that oxygen consumption decreased along a salinity gradient of 0-9 ppt.

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Citation for data on this website:
Grass Carp — Ctenopharyngodon idella.  Montana Field Guide.  .  Retrieved on , from