| Grass carp | |
|---|---|
| Juvenile Grass Carp | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Cypriniformes |
| Family: | Cyprinidae |
| Subfamily: | Squaliobarbinae |
| Genus: | Ctenopharyngodon Steindachner, 1866 |
| Species: | C. idella |
| Binomial name | |
| Ctenopharyngodon idella (Valenciennes in Cuvier & Valenciennes, 1844) |
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The grass carp (Ctenopharyngodon idella) is a herbivorous, freshwater fish species of family Cyprinidae, and the only species of the genus Ctenopharyngodon. It is cultivated in China for food, but was introduced in Europe and the United States for aquatic weed control (see, e.g., Ponchatoula Creek). It is a large cyprind native to eastern Asia, with a native range from northern Vietnam to the Amur River on the Siberia-China border.[1] It is a fish of large, turbid rivers and associated floodplain lakes, with a wide degree of temperature tolerance. Grass carp are usually thought to enter reproductive condition and spawn at temperatures of 20 to 30 °C (68 to 86 °F),[2] but have been shown to sometimes spawn at temperatures as low as 15 °C (59 °F).[3]
In the United States, the fish is also known as white amur, a name developed to avoid use of the name "carp", which has derogatory connotations in North America. The name derives from the Amur River, where the species is probably native, but has never been abundant.[4] This is not to be confused with the white amur bream (Parabramis pekinensis), which is not a particularly close relative as Cyprinidae.
For eating, the fish may be steamed, pan-fried, broiled, or baked.[5]
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Grass carp have elongate, chubby, torpedo-shaped body forms. The terminal mouth is slightly oblique with non-fleshy, firm lips, and no barbels.[6] The complete lateral line contains 40 to 42 scales. Broad, ridged, pharyngeal teeth are arranged in a 2, 4-4, 2 formula. The dorsal fin has 8 to 10 soft rays, and the anal fin is set closer to the tail than most cyprinids. Body color is dark olive, shading to brownish-yellow on the sides, with a white belly and large, slightly outlined scales.
The grass carp grows very rapidly, and young fish stocked in the spring at 20 centimetres (7.9 in) will reach over 45 centimetres (18 in) by fall, and adults often attain nearly 1.2 metres (3.9 ft) in length and over 18 kilograms (40 lb) in weight. According to one study, they live an average of five to 9 years, with the oldest gaining 11 years. [7] They eat up to three times their own body weight daily. They thrive in small lakes and backwaters that provide an abundant supply of freshwater vegetation.
This species occurs in lakes, ponds, pools and backwaters of large rivers, preferring large, slow-flowing or standing water bodies with vegetation.[8] In the wild, grass carp spawn in fast-moving rivers, and their eggs, which are slightly heavier than water, develop while drifting downstream, kept in suspension by turbulence. The eggs are thought to die if they sink to the bottom.[9]
Adults of the species feed primarily on aquatic plants. They feed on higher aquatic plants and submerged terrestrial vegetation, but may also take detritus, insects, and other invertebrates.[10][5]
The species was deliberately introduced into the United States in 1963 for aquatic weed control. It was introduced into New Zealand along with stocks of goldfish, but the distribution is carefully controlled to prevent it from becoming a more widespread pest.
The grass carp is considered an invasive species in the United States;[11] however, it is still stocked in many states as an effective biocontrol for undesirable aquatic vegetation, many species of which are themselves invasive. Grass carp require long rivers for the survival of the eggs and very young fish.
The species was introduced in the Netherlands in 1973 for overabundant aquatic weed control. The release into national waters is controlled and regulated by the Dutch Ministry of Agriculture, Nature and Food Quality. Because grass carp mainly reproduce in water of 25 °C (77 °F), which is much higher than the water temperature reaches during the mating season in the Netherlands, it is necessary to maintain grass carp populations by artificial means, which is done by the person responsible for the water body in which the fish were introduced. Where grass carp populations are maintained through stocking as a biocontrol for noxious weeds, they should be returned to the water alive and unharmed.
When used for weed control, often the fish introduced to the pond or stream are sterile, triploid fish. The process for producing triploid fish involves shocking eggs with a rapid change in temperature or pressure. This process is not usually 100% effective, therefore, in the United States, the young are usually tested for triploidy before being sold.[12] Bait often consists of vegetables or fruits that are native to the area.[13]
Grass carp grow large and are strong fighters on a rod and reel, but because of their vegetarian habits and their wariness, they can be difficult to catch.[14] Chumming with corn adds to success. Canned corn, cherry tomatoes, and, despite their primarily vegetarian habits, grass carp sometimes eat other vegetarians. Chumming with white bread, and a piece of bread pinched on a hook and floated on the surface works well, especially for pond grass carp. The fish are popular but wary quarry for bowfishers where bowfishing for grass carp is legal.
When searching for grass carp to fish, one may often spot fish cruising near the surface or very close to the shoreline. Often, an angler will spot a telltale swirl in the water near the shore without even glimpsing the fish. Grass carp often feed or rest near the shoreline, and are very wary in such places. They usually will dart away at the first sight of a person walking nearby. Stalking the fish to place a piece of bait nearby is sometimes successful. Casting bait on top of the fish usually results in spooking the fish.
Grass carp caught in ponds and lakes where they were stocked for weed control should be handled with care and released without harm.
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