British Wildlife Wiki

The Grass Carp (Ctenopharyngodon idella) is a herbivorous, freshwater fish species that belongs to the Carp Family. 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), but have been shown to sometimes spawn at temperatures as low as 15 °C (59 °F).

Grass carp


Grass carp

were introduced to the UK in the 1960s by a River Board (as it was then) hoping the fish would solve the problems with weed choking the waterways

Appearance and anatomy[]

Grass Carp have an elongate, chubby body form that is torpedo shaped. The terminal mouth is slightly oblique with non-fleshy, firm lips, and no Barbels. 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 5-9 years with the oldest gaining 11 years. They eat up to 3 times their own body weight daily. They thrive in small lakes and backwaters that provide an abundant supply of fresh water vegetation.


This species occurs in lakes, ponds, pools and backwaters of large rivers, preferring large, slow-flowing or standing water bodies with vegetation. 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.

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.

Relationship with humans[]

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, 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, but they have become very abundant in the large rivers of the central United States. Grass carp effects on their invaded environments are quite variable, with both desirable and undesirable effects.

The species was introduced in the Netherlands in 1973 for aquatic weed control against overabundant weed growth. The release of grass carp into national waters is controlled and regulated by the Dutch Ministry of Agriculture, Nature and Foodquality. 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 the fish were introduced in. Where grass carp populations are maintained through stocking as a biocontrol for noxious weeds, they should be returned into 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 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. Bait often consists of vegetables or fruits that are native to the area.

These fish are also a food fish, and may be steamed, pan fried, broiled, or baked.

Fishing for grass carp[]

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. Chumming with corn adds to success. Canned corn, cherry tomatoes, and, despite their primarily vegetarian habits, worms can sometimes be successful baits. However, by far the best method to catch them is to loosefeed (chum) with bread on the surface. This will attract both carp (if present) and grass carp. The grass carp, located by sight, can then be individually targetted by casting bread flake on a hook in front of them.