Photographer: Akos Harka Source: commons.wikimedia.org Copyright: (CC BY 3.0)
The Grass carp, Ctenopharyngodon idella, one of the 4 Asian Carp species present in the US, is one of the largest members of the minnow family. The body is oblong with moderately large scales, while the head has no scales. There are three simple and seven branched rays on the dorsal fin. Grass carp are silvery to olive in color, lacking the golden hue of common carp, and they have no barbels. This species typically reaches sizes of 65 to 80 pounds in its native habitat, but a few larger individuals have been caught.
Grass carp pose a substantial risk to non-native habitats. This is because Grass carp are explosive breeders and prodigious feeders (capable of consuming 40% to 300% of their body weight per day in plant material). Thus, Grass carp may out-compete indigenous species and take over novel habitats.
In addition, Grass carp may have potential to disrupt ecosystems in that they only digest about half of the 45kg of plant material that it consumes each day. The rest is expelled into the water as waste which can lead to an increase in nutrients with subsequent algal blooms. Algal blooms lower the water clarity and dissolved oxygen content.
Finally, Grass carp also harbor parasites that local species may not have a resistance to, which may lead to local extinction events and lasting changes in ecosystem dynamics.
Grass carp, like the other Asian carp species, are capable of invading new habitats due to their ability to produce numerous eggs and rapid growth. Unlike other carps, Grass carps prefer to spawn in large rivers instead of lakes or slower-moving water (however, Grass carp has the potential to breed in slower-moving water if need be). This is potentially dangerous as larger rivers flow through many states, which furthers the invasion.
Grass carp was first imported to the United States in 1963 to control macrophytes in aquaculture facilities in Alabama and Arkansas and, soon after, escaped into the open waters of Arkansas. By the early 1970s, there were many reports of grass carp captured in the Missouri and Mississippi. Since then, grass carp have spread rapidly as a result of widely scattered research projects, stockings by government agencies, unauthorized releases, interstate transport, escapes from farm ponds and aquaculture facilities and natural dispersal from introduction sites and the widespread stocking of grass carp as a biological control against nuisance aquatic plants in ponds and lakes.
Grass carp is a sub-tropical to temperate species, native to large rivers and lakes in eastern Asia. Its native range extends from southern Russia southward to northern Vietnam and from coastal waters inland.
U.S. Present: Grass carp have been recorded from 45 states; there are no reports of introductions in Alaska, Maine, Montana, Rhode Island, and Vermont. Breeding populations have been reported along major rivers including the Mississippi, Illinois, and the Trinity River in Texas.
U.S. Habitat: Grass carp are freshwater fish that prefer to spawn in large rivers with relatively turbid waters. Generally, the fish do not migrate great distances and prefer to congregate in specific areas, but migrants have been known to travel great distances in desperation. Due to their physiological plasticity, Grass carp can invade many different types of water habitats, and can consume various food sources. Usually, the Grass carp feed on plant material, which was the reason for their initial introduction.
Texas: Breeding populations have been established by escapees from legal experiments in Lake Conroe and illegal stocking. These fish are known to reproduce in the Trinity River-Galveston Bay area.
Resembles many of the carp species in the United States. Including its Asian cousins:
the Black carp (Mylopharyngodon piceus)
Silver carp (Hypophthalmichthys molitrix)
Largescale Silver carp (Hypophthalmichthys harmandi)
Bighead carp (Hypophthalmichthys nobilis)
Common Goldfish (Carassius auratus)
Crucian carp (Carassius carassius)
Mud carp (Cirrhinus molitorella)
Also resembles the Common carp (Cyprinus carpio)
Grass carp are potentially harmful to native resources. Currently, only triploid (sterile) Grass carp are legal for use in Texas, and a permit is required to obtain them. Since Grass carp is a potentially invasive species, an angler who catches one must immediately remove the intestines, except in waters where a valid Triploid Grass Carp Permit is in effect. In those waters, any Grass carp caught must be immediately returned to the water unharmed.
While triploid Grass carp are still used in macrophyte maintenance, they pose no threat of reproduction. However, diploid, viable Grass carp are still rampant throughout the United States and culling their numbers may prove a difficult task.
Allen Jr, S. K., & Wattendorf, R. J. (1987). Triploid grass carp: status and management implications. Fisheries, 12(4), 20-24
Hickling, C. F. "On the feeding process in the White Amur, Ctenopharyngodon idella." Journal of Zoology. 148.4 (1966): 408-419.
Beck, M. L., and C. J. Biggers. "Erythrocyte measurements of diploid and triploid Ctenopharyngodon idella×Hypophthalmichthys nobilis hybrids." Journal of Fish Biology. 22.4 (1983): 497-502.