Colorado Fish Species: Grass Carp

The Grass Carp are also called White Amur, belongs to the minnow family. A name developed and used to avoid the negative connotations of “carp.” This large import from China is primarily a freshwater herbivore introduced for aquatic weed control.  In many parts of the country it is considered an invasive species and stocking/transporting it is illegal.  However, it is still stocked for to control weeds, typically as sterile, triploid fish. The process to create sterility is not usually 100% effective, so the young are usually tested for triploidy before being sold.  
 
Amur have a torpedo shaped body with moderately large scales.  The head is scaleless. Coloring ranges from silver to olive in color on the back, shading to white on the belly. Its mouth is terminal, no barbells, with non-fleshy, firm lips. The dorsal fin has 8 to 10 soft rays. Anal fins are closer to the tail than most other minnows.
 
In its native habitat, Grass Carp are fish of large, turbid rivers and associated floodplains.  They have a wide degree of temperature tolerance. Spawn at occurs at temperatures 68 to 86 degrees Fahrenheit.  As these minnows spawn in flowing water and do not reproduce well in lakes and ponds. Reproductive success requires an adequate flow of oxygen rich water. Wild populations do exist in many waters of the United States.
 
 Juvenile grass carp rely primarily on phytoplankton for food, but have been reported to eat small invertebrates and crustaceans. Adults feed primarily on aquatic vegetation, consuming up to three times their weight in food each day. Grass carp are rapid growers, with fish stocked at eight inches in the spring reaching 18 inches by fall. Adults can obtain sizes in excess of four feet and fifty pounds. They are known to exceed one hundred pounds in China.