Where did the grass carp come from?
A native of eastern Asia, the grass carp was introduced in the U.S. in 1963 to control aquatic plants in fish farms. It was stocked in many locations by federal and state agencies as well as private individuals and researchers. Flooding of fish farms allowed some individuals to escape. They are now widely established.
Why is it a problem?
Grass carp eat large amounts of aquatic plants--up to 100% of their body weight per day. Large populations can remove the vegetation other fish need for food, shelter or spawning. Additionally, each fish can digest only about half of what it eats. The remaining material enriches the water and promotes algal blooms, which can reduce oxygen levels and water clarity. Grass carp may also carry parasites and diseases that cause problems for native fish.
What does the grass carp look like?
Large, with mature adults up to 49 inches long and weighing 99 pounds
Silvery dark grey body with a gold sheen on the side
Slightly downturned mouth with no barbels
Pointed dorsal fin with 8-10 soft rays.
Large, "chain-link" scales
What habitat does it prefer?
The grass carp tolerates a wide range of temperatures, from freezing to over 100*F. It also can tolerate low oxygen levels and brackish water. It prefers large standing or slow-flowing water with vegetation.
For more photos and information about the grass carp, see the Wisconsin Fish Identification tool.