Invasive Species Notes:
Triploid Grass Carp/White Amur
(Ctenopharyngodon idella Val.)
Mandy Tu
©The Nature Conservancy’s Wildland Invasive Species Team
March 21, 2003
Summary:
Grass carp, also called white amur, are native to eastern Asia (Russia and China) and have been introduced into
more than 50 countries for aquatic weed control and aquaculture. In the U.S., grass carp were first introduced into
Alabama and Arkansas aquaculture facilities in 1963, and escaped shortly afterwards (in 1966) from the Fish
Farming Experimental Station in Stuttgart, Arkansas. By the early 1970s, there were several reports of grass carp
captured from the Missouri and Mississippi rivers (Nico & Fuller 2001). Currently, grass carp populations are
present in 45 U.S. states, with known reproductive populations in the Mississippi River, the Illinois River, the
Missouri River, and in the Ohio River (Nico & Fuller 2001; Poss 2000).
Uses:
In the U.S., grass carp were (and are still) often introduced to control submersed aquatic weeds such as Hydrilla
verticillata and Egeria densa. Grass carp can be used as part of an integrated management program to control
aquatic vegetation, and they are a long-term control method that is relatively inexpensive and provides highly
effective control for certain species. Depending on the stocking rate, macrophyte abundance (availability of food),
and community structure of the ecosystem, however, grass carp can have harmful effects such as consuming all the
vegetation, including desirable species.
Potential Negative Impacts:
Grass carp may consume all aquatic vegetation and overhanging terrestrial vegetation, thereby reducing food
available to native invertebrates and other fishes. This may result in additional significant changes in the
composition of macrophyte, phytoplankton and invertebrate communities, altering food webs and the trophic
structure of these aquatic systems. Further, grass carp often increase phytoplankton populations by enriching the
system with their undigested and expelled plant material, promoting algal blooms that reduce water clarity and
decrease oxygen levels (Bain 1993; Rose 1972). Grass carp may also carry several parasites and diseases known to
be transmissible or potentially transmissible to native fishes. It is believed that grass carp from China are the
primary source and vector for Asian tapeworms - Bothriocephalus opsarichthydis (Hoffman & Schubert 1984).
Reproductive Rates
Grass carp have tremendous reproductive capacities. In its native range in the Amur Basin, reproductively mature (7
to 15+ yr old) female grass carp produce an average of 820,000 eggs (Gorbach 1972). Fecundity is lowest in first
time spawners and highest in large females that have spawned repeatedly. In European latitudes, average fecundity
ranged between 500,000 to 700,000 eggs per fish that weighed 6 to 8 kg, respectively (Vovk 1968, in: Poss 2000).
Sterile Triploids
Grass carp are naturally diploid (2N=48), but because of the above-mentioned negative impacts of unwanted
population expansions, sterile triploids (3N= 72) were developed to create non-reproductive fish. Hydrostatic
pressure is the most consistent method for widespread commercial production of triploid grass carp, but this type of
treatment seldom results in 100% triploidy (Rottmann et al. 1991). Hence, many states require that each individual
fish must be verified to be triploid before it can be stocked in waters. Although putatively non-reproductive, these
triploids retain their voracious, herbivorous diet. So even though sterile triploids will not reproduce, they may still
consume all available vegetation.
There is no published information on the viability of eggs from triploid females, but milt from triploid males has
been found to successfully fertilize normal diploid eggs (Howells 1992). The proportion of viable male gametes is
extremely low, so triploid carp are often referred to as being functionally sterile, with only 0.00000012 of the
gametes fertile (i.e. about 1 out of 8 million gametes are fertile) (Poss 2000).
To Prevent Escape
Screens or gates at all inflows and outflows must be installed to prevent the escape of grass carp. Once established,
grass carp are extremely difficult to remove. Grass carp can easily move beyond the areas where it was introduced
and are known to migrate up to 1,700 km within a single season (Guilory & Gasaway 1978).
Naturalized populations of grass carp in the U.S. (Image by Liz McKercher,
USGS Nonindigenous Aquatic Species Program, Gainesville, FL.).
References
Bain, M.B. 1993. Assessing impacts of introduced aquatic species: Grass carp in large systems. Environmental
Management 17(2): 211-224.
Gorbach, E.I. 1972. Fecundity of the grass carp [Ctenopharyngodon idella (Val.)] in the Amur Basin. Journal of
Ichthyology 12(4): 616-625.
Howells, R.G. 1992. Guide to identification of harmful and potentially harmful fishes, shellfishes and aquatic
plants prohibited in Texas. Texas Parks and Wildlife Department Special Publication, Austin, TX. 182 pp.
Hoffman, G.L. and G. Schubert. 1984. Some parasites of exotic fishes. Pages 233-261 in W. R. Courtenay, Jr., and
J. R. Stauffer, Jr., editors. Distribution, biology, and management of exotic fishes. The Johns Hopkins
University Press, Baltimore, MD.
Nico, L. and P. Fuller. 2001. Nonindigenous Aquatic Species: Ctenopharyngodon idella. USGS Center for
Aquatic Resource Studies. Available at http://nas.er.usgs.gov/fishes/accounts/cyprinid/ct_idell.html. Accessed
March 10, 2003.
Poss, S.G. 2000. Species summary for Ctenopharyngodon idella. Gulf States Marine Fisheries Commission
(GSMFC). Available at http://gsmfc.org/nis/nis/Ctenopharyngodon_idella.html.
Rose, S. 1972. What about the white amur? A superfish or a supercurse? Florida Naturalist 1972:156-157.
Rottmann, R.W., Shireman, J.V. and F.A. Chapman. 1991. Induction and verification of triploidy in fish. Southern
Regional Aquaculture Center, Publication No. 427.
Sutton, D.L. and V.V. Vandiver, Jr. 2000. Grass carp: A fish for biological management of Hydrilla and other
aquatic weeds in Florida. University of Florida Cooperative Extension Service, Bulletin #867. Available at
http://edis.ifas.ufl.edu/BODY/FA043. Accessed March 10, 2003.