Grass Carp

Characteristics

Elongate, chubby body that is torpedo-shaped. The body is dark olive, shading to brownish-yellow on the sides with a white belly and large, slightly outlined scales. The terminal mouth is slightly oblique with non-fleshy, firm lips, and no barbels. The complete lateral line has 40 to 42 scales. The dorsal fin has 8 to 10 soft rays, and the anal fin is set closer to the tail than most cyprinids. Broad, ridged pharyngeal teeth are arranged in a 2, 4-4, 2 formula.

Distribution

Widely distributed throughout Iowa in ponds and man-made lakes, but it is not abundant in any location. Commercial fishermen report rare catches of Grass Carp from the Mississippi and Missouri Rivers. Primarily a big river fish, it has been found in the Mississippi and Missouri Rivers. It often escapes from ponds and impoundments where it is stocked and has also occasionally been found in Iowa’s interior rivers and streams, including streams in the Skunk, lower Iowa, Maquoketa and Winnebago River watersheds.

Foods

Aquatic macrophytes, and since they are voracious feeders, they are used to control aquatic invasive plants in small lakes and pond. They are not effective in controlling filamentous algae (moss) or duckweed problems in ponds.

State Record

85 lbs 8 oz, 48 in.- Greenfield Lake, Adair County, May 1, 2007 - Jesse Lane, Greenfield, IA

Expert Tip

None

Details

Grass Carp is an exotic minnow that was imported into the United States from eastern Asia in 1963 to control aquatic invasive plants. They were first brought to Iowa in 1973 by the Iowa Conservation Commission. Research conducted in Iowa has shown that Grass Carp have harmful effects on water quality and fish habitat; the Iowa DNR no longer stocks Grass Carp in public water bodies.

The Grass Carp is most often found in large rivers, but is stocked in impoundments, ponds and lakes. It prefers swift, warm waters with slack current and aquatic plants. In its native habitat, Grass Carp prefer turbulent reaches of large rivers. Some investigators are concerned because the Grass Carp’s big appetite for aquatic plants may lead to the destruction of suitable habitat for many native fish and waterfowl. 

Grass Carp have specialized and restrictive river spawning needs, but young fish have been sampled in Iowa rivers. Natural spawning is impossible in standing water. Growth of Grass Carp is nearly unbelievable, young fish stocked in the spring at 8-inches will reach over 18-inches by fall, and adults often reach nearly 4-feet long and over 40-pounds. 

Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.

Sources:

Harlan, J.R., E.B. Speaker, and J. Mayhew. 1987. Iowa fish and fishing. Iowa Conservation Commission, Des Moines, Iowa. 323pp.

Loan-Wilsey, A. K., C. L. Pierce, K. L. Kane, P. D. Brown and R. L. McNeely. 2005. The Iowa Aquatic Gap Analysis Project Final Report. Iowa Cooperative Fish and Wildlife Research Unit, Iowa State University, Ames.

Photo Credit: photo courtesy of Noel M. Burkhead, copyright Noel M. Burkhead, USGS, Nonindigenous Aquatic Species.