Description
Most fish stocked in the United States now are sterile triploids, produced by subjecting eggs to a temperature shock after fertilization, resulting from retention of the second polar body and an extra set set of chromosomes. This results in increased cell size; red blood cells are used for testing. Electronic particle sizers are used to verify triploidy and for inspection of eggs by the United States Fish and Wildlife Service, which certifies fish as triploid (Allen and Wattendorf 1987; Griffin 1991).
Taxonomy
| Kingdom | Phylum | Class | Order | Family | Genus |
|---|---|---|---|---|---|
| Animalia | Chordata | Osteichthyes | Cypriniformes | Cyprinidae | Ctenopharyngodon |
Synonyms
Invasion History
Chesapeake Bay Status
| First Record | Population | Range | Introduction | Residency | Source Region | Native Region | Vectors |
|---|---|---|---|---|---|---|---|
| 1989 | Unknown | Expanding | Introduced | Regular Resident | East Asia | East Asia | Biocontrol(Biocontrol) |
History of Spread
Ctenopharyngodon idella (Grass Carp) is native to lowland rivers of China and the Amur basin of the former USSR. This fish has been introduced worldwide for aquaculture and aquatic weed control and is now established in the wild in Africa, Russia, Japan, Mexico, and possibly in the Phllippines and Yugoslavia (Shireman and Smith 1983; Lever 1996). In North America, it was first imported from Malaysia to the United States Fish and Wildlife Service Fish Farming Experimental station in 1963. When this species was first imported, it was believed that this fish's reproductive requirement for large swift-flowing rivers would prevent its establishment in North America (Courtenay 1993). It escaped in the vicinity of the station, and was deliberately released later, for weed control (Lake Brimley AR; 1968) , and became established in the lower Mississippi drainage (Robison and Buchanan 1988). By 1978 C. idella had spread or been introduced to 35 states, although reproduction had not then been confirmed (Guillory and Gasaway 1978). They have now been found in 45 states (Florida Caribbean Science Center 2001). Larvae and juveniles were found in the Mississippi by 1980, and C. idella were apparently reproducing extensively in IL and upper Mississippi River by the 1990s (Raibley et al. 1995).
While C. idella are regarded as a threat to native submerged vegetation, they have also proved useful for controlling aquatic weeds (mostly exotics) in reservoirs and waterways, as an alternative to draining, mechanical cutting, or herbicides (Bain 1993). This dilemma led to efforts to develop nonreproductive fish for weed control. Early attempts through hybridization with other Asian carps were unsuccessful, but eventually techniques were developed to produce sterile triploids induced through cold shock or pressure. The U.S. Fish and Wildlife Service developed a certification program to test for triploidy in batches of fish to be stocked (Allen and Wattendorf 1987). State policies vary greatly with regard to this species. Ctenopharyngodon idella is now banned altogether in 18 states; stocking of triploids is permitted by United States Fish and Wildlife Service and by 14 states; 4 states allow importation of triploids only for closely regulated experimental use (Allen and Wattendorf 1987). Private, illegal stockings of sterile and fertile fish have occcurred in many states (Bain 1993; Jenkins and Burkhead 1993).
In the Chesapeake Bay watershed, diploid C. idella were stocked by private individuals in Potomac tributaries in the 1970s (Guillory and Gasaway 1978). A diploid population near Charlottesville VA was eradicated by the Virginia Department of Game and Inland Fisheries (Jenkins and Burkhead 1993). In the 1980s, triploid (sterile) fishes have been released in several VA (e.g. Lake Burke, Fairfax County) and DE reservoirs and ponds for vegetation control in 1983-1987 (Raasch and Altemus 1991; Jenkins and Burkhead 1993). At present, diploid, fertile C. idella are banned throughout the Chesapeake watershed. Stocking of certified triploid fish, with permits, is legal in VA, WV, PA and NY; only certified triploids can be imported. All C. idella are illegal in MD, DE and PA (Christmas et al. 2001).
Scattered introductions of C. idella have occurred through the watershed since the 1970s, but reproduction has not been documented (Jenkins and Burkhead 1993). The first record which we have documented from tidal waters was a fish collected by Maryland Department of Natural Resources in 1989, in the Potomac River, in Geogetown DC (Kazyak 1995). The fertility of the fish is not known.
A proposed stocking of 6300 certified triploid C. idella, to control submerged vegetation in powerplant cooling lagoons adjacent to Lake Anna VA (York River drainage) aroused concerns over the threat to submerged aquatic vegetation (SAV) in Chesapeake Bay from possible establishment of this fish (Terlizzi 1996). Modelling studies suggested that intensive stocking of C. idella in the Chesapeake watershed, would result in some inadvertent release of diploid fish (Jacobson and Kartalia 1994). In a compromise addressing these concerns, the Chesapeake Bay Commission required a more intense inspection (of each individual fish, rather than sampling) for this stocking (Terlizzi 1996). Schultz et al. (2001) examined the ploidy and fertility of 11 C. idella captured in the Chesapeake Bay watershed. Two of these fish, both female, from the Mattaponi (York) River VA and the Patuxent River MD, were diploid, indicating that illegal releases of potentially fertile C. idella are occurring in the watershed. Gonadal development was also seen in 4 triploid individuals, but these triploid fish are very unlikely to produce viable offspring (Schultz et al. 2001).
History References - Allen and Wattendorf 1987; Bain 1993; Courtenay et al. 1984; Florida Caribbean Science Center 2001; Guillory and Gasaway 1978; Jacobson and Kartalia 1996; Jenkins and Burkhead 1993; Kazyak 1995; Lever 1996; Raasch and Altemus 1991; Raibley et al. 1995; Robison and Buchanan 1988; Schultz et al. 2001; Shireman and Smith 1983; Terlizzi 1996
Invasion Comments
Population Status - Given the putative sterility of populations in the Chesapeake drainage, this species could be treated as a either failed invader, or a potential one. Accidents or cheating are possible in the process of commercially producing 'certified' triploid fishes for distribution, although the inspection and certification process greatly reduces this risk (Allen and Wattendorf 1987). Illegal introductions of diploid fishes or dispersal from reproducing populations elsewhere are also possible.
Ecology
Environmental Tolerances
| For Survival | For Reproduction | |||
|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | |
| Temperature (ºC) | 0.1 | 40.0 | 19.0 | 31.0 |
| Salinity (‰) | 0.0 | 11.0 | 0.0 | 0.2 |
| Oxygen | hypoxic | |||
| pH | 5.0000000000 | 9.0000000000 | ||
| Salinity Range | fresh-oligo |
Age and Growth
| Male | Female | |
|---|---|---|
| Minimum Adult Size (mm) | 510.0 | 580.0 |
| Typical Adult Size (mm) | 900.0 | 900.0 |
| Maximum Adult Size (mm) | 1100.0 | 1100.0 |
| Maximum Longevity (yrs) | 21.0 | 21.0 |
| Typical Longevity (yrs | 8.0 | 8.0 |
Reproduction
| Start | Peak | End | |
|---|---|---|---|
| Reproductive Season | |||
| Typical Number of Young Per Reproductive Event |
|||
| Sexuality Mode(s) | |||
| Mode(s) of Asexual Reproduction |
|||
| Fertilization Type(s) | |||
| More than One Reproduction Event per Year |
|||
| Reproductive Startegy | |||
| Egg/Seed Form |
Impacts
Economic Impacts in Chesapeake Bay
Ctenopharyngodon idella (Grass Carp) does not have any known reproductive populations in the Chesapeake Bay watershed. Except for stray, probably sterile, individuals, C. idella are absent from Chesapeake Bay tidal waters at present. However, reproduction of stocked triploid populations in the watershed is a serious concern because of the threat to native submerged aquatic vegetation in the Bay (Jacobson and Kartalia 1994). Impacts observed in other systems include:
Aesthetic - C. idella provide a substantial benefit in reservoirs due to reduction of rafted weeds on shorelines, improved quality for swimming, etc. Their use avoids rapid die-off and decay of vegetation which results from herbicide use (Bain 1993).
Fisheries - In lakes and reservoirs, use of sterile C. idella avoids the incidental mortality that occurs with mechanical harvesting or herbicides (Bain 1993), and at much lower costs. (Allen and Wattendorf 1987). There could be possible benefits due to reduction in Hydrilla verticillata in some areas (upper Potomac), but adverse fisheries effects of H. verticllata and other submerged aquatic vegetation (SAV) in the Chesapeake are already limited by winter dieback, turbidity, etc. (See the species account for Hydrilla verticllata. Submerged aquatic vegetation is regarded as essential to recruitment of commercial and sport fishes in Chesapeake Bay, so introduction of fertile or large quantities of sterile C. idella would have largely adverse effects. C. idella rarely take a hook (Robison and Buchanan 1988) so they are unimportant as a sport fish. They are fished commercially in AR (68 tons caught annually in 1984; Robison and Buchanan 1988), and are claimed to have a high market value (Pierce 1983), but 'We have found the quality of its flesh for eating to be highly variable. Sometimes it is tainted with a strong algal flavor' (Robison and Buchanan 1988).
Results of C. idella introductions for fisheries improvement appear to be variable, and appear to be highly dependent on stocking density (Taylor et al. 1984). In open river systems, and in particular, with fertile fish, controlled introductions are impossible.
Boating - In the early stages of H. verticllata's invasion in the Potomac, C. idella were considered for H. verticillata control for navigation in Potomac estuary, but rejected due to impossiblity of control in an open system (Anonymous 1994).
Health - C. idella provide possible benefits in water supply reservoirs by removing excess vegetation, and also by reduction of mosquito larval habitats (Pierce 1983).
Habitat Change - See Fisheries, Ecological impacts, above.
References - Allen and Wattendorf 1987; Anonymous 1994; Bain 1993; Pierce 1983; Robison and Buchanan 1988; Taylor et al. 1984
Economic Impacts Outside of Chesapeake Bay
Introduction of fertile Ctenopharyngodon idella (Grass Carp) into many parts of North America is frequently seen as a serious error. Large populations can rapidly eliminate aquatic vegetation, and breeding greatly complicates population control (Allen and Wattendorf 1987). This fish is extremely mobile, and can be expected to colonize most or all of a river drainage to which it is introduced (Courtenay et al. 1984; Raibley et al. 1995). State regulations on C. idella introductions vary greatly, even within river basins. Coordination of state policies within watersheds, or federal policies are desirable, given this species' ability to cross state lines (Allen and Wattendorf 1987).
In lakes and reservoirs the environmental risks of sterile C. idella introduction for weed control are widely regarded as small compared to those of herbicides, mechanical harvesting, etc (Allen and Wattendorf 1987; Bain 1993). Bain (1993) provides a good example of a qualitative cost-benefit study of sterile C. idella introductions as a means of vegetation control in a reservoir. Induction of triploidy combined with automated methods of verification greatly decrease the risk of fertile fish being inadvertantly introduced (Allen and Wattendorf 1987). However, error and cheating are hard to exclude or calculate. On a watershed-wide basis, the risks are multiplied by the numbers of reservoirs treated.
References - Allen and Wattendorf 1987; Bain 1993; Courtenay et al. 1984; Raibley et al. 1995
Ecological Impacts on Chesapeake Native Species
Ctenopharyngodon idella (Grass Carp) does not have any known reproductive populations in the Chesapeake Bay watershed. Except for stray, probably sterile, individuals, C. idella are absent from Chesapeake Bay tidal waters at present. However, the establishment of reproducing populations is considered a danger to native submerged aquatic vegetation (SAV) in the Bay. Potentially reproductive populations in MD and VA ponds have been eradicated (Lee et al. 1981; Jenkins and Burkhead 1993). All C. idella are illegal in MD, while only certified triploid fish are legal in VA, DE, PA, and WV (Christmas et al. 2001). A modelling study suggests that intensive stocking of certified triploid fish poses a substantial risk of inadvertent introduction of reproductive individuals (Jacobson and Kartalia 1994). Consequently, the Chesapeake Bay Commission has required more intense inspection for C. idella released in an expanded stocking program (Terlizzi 1996).
Herbivory- C idella are widely introduced for control of aquatic weeds (usually exotic). However, if the stocking density is too high, and/or the 'target plant' is one not preferred by C. idella, C. idella can elimiante naitve vegetation whiich may be valuable for wildlife (Pierce 1983; Taylor et al. 1984). Among the native species, adversely affected by C. idella, in experimental enclosures in an AL reservoir, were the submersed plants Potamogeton sp. (Pondweed), Najas guadalupensis (Water-Nymph), Ceratophyllum demersum (Coontail), the alga Chara sp., and the emergent sedge Eleocharis acicularis (McKnight and Hepp 1995).
Competition - Ctenopharyngodon idella is a potential competitor with ducks, coots, and muskrats (suggested by Bain 1993; Raibley et al. 1995; Shireman and Smith 1983). McKnight and Hepp (1995) showed, using exclosures, that grazing by C. idella in an AL reservoir increased the proportion of biomass of Eurasian milfoil (Myriophyllum spicatum) in mixed stands of vegetation, by selectively removing native plants preferred by waterfowl.
Habitat Change - C. idella has potentially wide-ranging effects due to vegetation removal, but also due to the recycling of previously uneaten vegetation, alteration of foodwebs, etc. Ideally, controlled stocking could benefit native fish communities, by removing excessive plant biomass, decreasing organic matter loads, increased dissolved oxygen, increasing space for mobile predatory fishes, etc. (Pierce 1983; Taylor et al. 1984). Effects of C. idella stocking programs on sportfish production in ponds and lakes vary, including increase, reductions, and no detectable change (Taylor et al. 1984). Pierce (1983) emphasizes the positive effects, but at high densities in eutrophic systems, elimination of macrophytes can result in blooms of planktonic algae. In riverine systems, vegetation reduces sediment resuspension, turbidity, etc., as well as providing habitat for invertebrates and juvenile fishes, etc. (Raibley et al. 1995).
Food/Prey - Juvenile C. idella may be especially vulnerable to predators [especially Micropterus salmoides (Largemouth Bass)]; possibly in part accounting for the scarcity of young, even in rivers with established populations, and for the difficulty of verification of natural reproduction (Raibley et al. 1995). In order to reduce predation losses, stocked fish over 450 mm are recommended for weed control (Taylor et al. 1984).
References - Bain 1993; Jacobson and Kartalia 1994; Jenkins and Burkhead 1993; Lee et al. 1981; McKnight and Hepp 1995; Pierce 1983; Raibley et al. 1995; Shireman and Smith 1983; Taylor et al. 1984; Terlizzi 1996
Ecological Impacts on Other Chesapeake Non-Native Species
Ctenopharyngodon idella (Grass Carp) does not have any known reproductive populations in the Chesapeake Bay watershed. Except for stray, probably sterile, individuals, C. idella are absent from Chesapeake Bay tidal waters at present. However, they are used for biocontrol of exotic aquatic weeds in VA and DE reservoirs.
Herbivory - C. idella are widely introduced for control of aquatic weeds, especially Hydrilla verticillata (Hydrilla), Egeria densa (Brazilian Waterweed) and Eichornia crassipes (Water Hyacinth). Najas minor (Eurasian water-Nymph) was also among species eaten (Shireman and Smith 1983). Introductions around the Washington D.C. area have been primarily for Hydrilla control (Jenkins and Burkhead 1993). Myriophyllum spicatum (Eurasian Watermilfoil) is less preferred, ('typically the last species grass carp consume' (Bain 1993), and may even benefit from C. idella introduction (McKnight and Hepp 1995; Shireman and Smith 1983).
Habitat Change - C. idella have been frequently introduced to improve habitat for Micropterus salmoides Micropterus salmoides(Largemouth Bass) where these populations have been threatened by excessive weed growth (Bain 1993). However, actual effects on gamefish populations have been mixed (Taylor et al. 1984).
References - Bain 1993; McKnight and Hepp 1995; Shireman and Smith 1983; Taylor et al. 1984
References
Allen, Standish K., Wattendorf, Robert J. (1987) Triploid grass carp: Status and management implications, Fisheries 12: 20-24Anonymous (1994) It's harvest season in the Potomac, Water Environment - Technology 6: 24-25
Bain, Mark B. (1993) Assessing impacts of introduced aquatic species: grass carp in large systems, Environmental Management 17: 211-224
Courtenay, Walter R., Jr.; Hensley, Dannie A.; Taylor, Jeffrey; McCann, James A. (1984) Distribution of exotic fishes in the continental United States., In: Courtenay, Walter R., and Stauffer, Jay R.(Eds.) Distribution, Biology, and Management of Exotic Fishes. , Baltimore, MD. Pp.
1996 Nonindigenous Aquatic Species Database. http://nas.er.usgs.gov/
Fuller, Pam. L.; Nico, Leo; Williams, J. D. (1999) Nonindigenous fishes introduced into inland waters of the United States, , Bethesda MD. Pp.
Griffin, B. R. (1991) The U. S. Fish and Wildlife Service's triploid grass carp inspection program, Aquaculture Magazine 17: 69-72
Guillory, Vincent; Gasaway, Robert D. (1978) Zoogeography of the grass carp in the United States, Transactions of the American Fisheries Society 107: 105-112
Jacobson, Paul T.; Kartalia, Stephen D. (1994) Ecological risk assessment of the effects of grass carp on submerged aquatic vegetation in Chesapeake Bay., In: Hill, Paula; Nelson, Steven(Eds.) Toward a Sustainable Coastal Watershed: The Chesapeake Experiment. Proceedings of a Conference. , Baltimore, MD. Pp. 378-383
Jenkins, Robert E.; Burkhead, Noel M. (1993) Freshwater fishes of Virginia., , Bethesda, MD. Pp.
1995 Telephone conservation- Nonindigenous fishes in the Chesapeake Bay watershed.
Lee, David S.; Gilbert, Carter R.; Hocutt, Charles H.; Jenkins, Robert E.; McAllister, Don E.; Stauffer, Jay R. (1980) Atlas of North American Freshwater Fishes, , Raleigh. Pp.
Lever, Christopher (1996) Naturalized fishes of the world., , London, England. Pp.
Maceina, M. J.; Nordlie, F. G.; Shireman, J. V. (1980) The influence of salinity on oxygen consumption and plasma electrolytes in grass carp, Ctenopharyngodon idella Val., Journal of Fish Biology 16: 613-619
McKnight, S. Keith; Hepp, Gary R. (1995) Potential effect of grass carp herbivory on waterfowl foods, journal of Wildlife Management 59: 720-727
Page, Lawrence M.; Burr, Brooks M. (1991) Freshwater Fishes., , Boston. Pp.
Pierce, Barry A. (1983) Grass carp status in the United States: a review, Environmental Management 7: 151-160
Raasch, Maynard S.; Altemus, Vaughn L., Sr. (1991) Delaware's freshwater and brackish water fishes: a popular account, , Wilmingotn, Delaware. Pp.
Raibley, Paul T.; Blodgett, Douglas; Sparks, R. E. (1995) Evidence of grass carp (Ctenopharyngodon idella) reproduction in the Illinois and upper Missisippi River, Journal of Freshwater Ecology 10: 65-74
Robison, Henry W.; Buchanan, Thomas M. (1988) Fishes of Arkansas, , Fayetteville, AR. Pp.
Schultz, Summer L.; Steinkoenig, Ed. L.; Brown, Bonnie L. (2001) Ploidy of feral grass carp in the Chesapeake Bay watershed, North American Journal of Fisheries Management 21: 96-101
Shireman, Jerome V.; Smith, Charles R. (1983) Synopsis of biological data on the grass carp Ctenopharynogodon idella (Cuvier and Valenciennes, 1844), , Rome. Pp.
Taylor, Jeffrey; Courtenay, Walter R.; McCann, James A. (1984) Known impacts of exotic fishes in the continental United States., , Baltimore, MD. Pp. 323-373
Terlizzi, Daniel E. (1996) Toward regional management of aquatic nuisance species in the Chesapeake Bay basin, Aquatic Nuisance Species Digest 1: 38, 46-47