Adopt-A-Carp :: Lake Norman Hydrilla Control Project

Commonly known as the white amur, amur, or sogyo (in Japan), the asian grass carp isn't actually a "carp" but is actually a large member of the minnow family (Ctenopharyngodon idella) and an aquaculture species of worldwide importance.

Introduced in the 1960s in the United States, the grass carp is used as weed control because of its aggressive and herbivorous feeding habits on aquatic plants and grasses.

The grass carp stocked in Lake Norman are sterile carp, known as "triploids." Should you accidentally catch a grass carp, you should immediately release the fish back into the water. The Lake Norman Marine Commission passed an ordinance in September 2004 making possession of the Sterile Asian Grass Carp illegal. This ordinance is enforceable by all state, county and city authorities that patrol Lake Norman. The ordinance was passed because each Sterile Grass Carp costs between $ 5.00 to $ 12.00 each. For each fish caught is another fish that we must replace.

Triploid Grass Carp are unable to reproduce. This makes the population manageable.
(Photo courtesy of the Marine Commission.)

In 1981, researchers developed a technique that consists of exposing fertilized eggs to heat shock which produce sterile grass carp. This method creates non-reproducing fish of both genders called triploid grass carp because they have three sets of chromosomes, instead of the usual two sets, which are called diploid. They are as hardy as the ordinary variety of grass carp, but they have the benefit of not being able to overpopulate their habitats. They flourish in warm water, and may reach weights of 25 pounds or more. Triploid grass carp are useful in controlling unwanted aquatic plants, as their numbers are easily managed with careful monitoring.

Primarily vegetarians, grass carp have earned their name by eating aquatic plants and submerged grasses, with the addition of an occasional insect or invertebrate. With the help of teeth on the pharynx, they tear off vegetation with jerking motions of their bodies. Unlike common carp, grass carp do not muddy the water with their browsing.

Should you catch a grass carp, it should be released immediately.
(Photo courtesy of the Marine Commission.)

The grass carp has an elongated and compressed body, a blunt wide head, a very short snout without the barbels found on common carp, a short dorsal fin, and a moderately forked tail. The terminal and non-protractile mouth has thin lips and sharp pharyngeal (throat) teeth especially suited to eating vegetation. The grass carp is covered with large scales; the ones on the upper sides of the body have a dark border and a black spot at the base, and give the fish a cross-hatched appearance. It is colored gray or green on the back, shading to white or yellow on the belly with clear to dark fins.

The grass carp grows quickly and to large sizes, some reported at 100 pounds in native waters. It can add 3 to 5 pounds a year to its weight under favorable conditions. The triploid grass carp in Lake Norman shouldn't reach more than 25 or 30 pounds.

Found originally in China and eastern Siberia, specifically in the Amur River basin from which it gets its name, the grass carp has been widely introduced to over twenty countries. Only those in certain areas have been able or allowed to reproduce naturally; these places include the Danube River in Central Europe, the Mississippi River in North America, and Russia and southern Africa. In the United States, it was first stocked in Arkansas waters in 1963 and intentionally released in thirty-five states, though it has subsequently spread to other bodies of water where it was unwanted. In fact, many states have made it illegal to stock grass carp within their borders, unless a permit issued by the appropriate fisheries management agency has been obtained.

Occurring in freshwater, grass carp inhabit lakes, ponds, pools, and backwaters of large rivers, with a preference for slow-flowing or standing bodies of water with vegetation. They are able to withstand temperature variation, extreme salinities, and low oxygen concentrations.