Grass carp

The grass carp (Ctenopharyngodon idella) is a species of large herbivorous freshwater fish in the family Cyprinidae, native to the Pacific Far East, with a native range stretching from northern Vietnam to the Amur River on the Sino-Russian border. This Asian carp is the only species of the genus Ctenopharyngodon.

Grass carp are resident fish of large turbid rivers and associated floodplain lakes/wetlands with a wide range of temperature tolerance, and spawn at temperatures of 20 to 30 °C (68 to 86 °F). It has been cultivated as a food fish in China for centuries, being known as one of the "Four Great Domestic Fish" (Chinese: 四大家鱼), but was later introduced to Europe and the United States for aquatic weed control, becoming the fish species with the largest reported farmed production globally, over five million tonnes per year.

The grass carp is the only extant member of the genus Ctenopharyngodon, but two other extinct species in the genus are known from Early Miocene-aged fossil teeth from China: †Ctenopharyngodon orientalis Su, Chang & Chen, 2021 (Xiacaowan Formation of Hebei) and †Ctenopharyngodon xiejiaensis Su, Chang & Chen, 2021 (Xiejia Formation of Qinghai). The earliest fossil teeth of the modern grass carp (C. idella) appear in the Early Pliocene-aged Gaozhuang Formation of Shanxi. Two other extinct genera that appear to be related to grass carp, †Eoctenopharyngodon and †Dezaoia, are known from the Oligocene of China.

Grass carp have elongated, chubby, torpedo-shaped body forms. 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 eight to 10 soft rays, and the anal fin is set closer to the tail than most cyprinids. The body color is dark olive, shading to brownish-yellow on the sides, with a white belly and large, slightly outlined scales.

Grass carp grow very rapidly. Young fish stocked in the spring at 20 cm (7.9 in) will reach over 45 cm (18 in) by fall. The typical length is about 60–100 cm (23.5–39.5 in). The maximum length is 2.0 m (6.6 ft) and they grow to 45 kg (99 lb).

Grass carp inhabit lakes, ponds, pools and backwaters of large rivers, preferring large, slow-flowing or standing water bodies with abundant 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. Grass carp require long rivers for the survival of the eggs and very young fish, and the eggs are thought to die if they sink to the bottom.

Adult grass carps feed primarily on aquatic plants, both higher aquatic plants and submerged terrestrial vegetation, but may also eat detritus, insects and other invertebrates. They eat up to three times their own body weight daily, and thrive in small lakes and backwaters that provide an abundant supply of vegetation.^{[citation needed]}

According to one study, grass carp live 5–9 years, with the oldest surviving 11 years. In Silver Lake, Washington, a thriving population of grass carp is passing the 15-year mark.