Aquatic Weed Control: Using Grass Carp

Carp, or white amur, have been used for aquatic vegetation control in Mississippi for the past two decades. These fish, used as a "biological control" for aquatic vegetation, can be effective and cost efficient when stocked at appropriate rates and when the problem-weed species is a plant preferred by carp. Although these fish are voracious herbivores, they exhibit preferences for the softer, low-fiber, high-moisture plants when given a choice. Even when there is no alternative, grass carp will not always provide adequate control of certain plants that they do not prefer to eat.

It is important to identify the problem plant(s) properly and to choose to stock grass carp only when the problem plants are those that grass carp are proven to control. A number of studies have determined grass carp preferences of the various common aquatic plants, and results from some of that work are summarized in this publication. In some cases, although grass carp are listed in the scientific literature as preferring a certain weed, field experience in Mississippi shows them to be ineffective on a consistent basis. Those plants that grass carp do not consistently control are rated as "low" in effectiveness (Table 1).