White Amur for Aquatic Weed Control

Grass carp (Ctenopharyngodon idella), or white Amur, is a member of the minnow family native to the Amur River region in Asia. They feed almost exclusively on aquatic plants. Their short digestive tract requires grass carp to feed almost continuously when water temperatures are above 68ºF, which means they can eat two to three times their body weight each day. This makes them an excellent biological control of certain nuisance aquatic plants.

Grass carp are capable of fast growth and may gain 5 to 10 lb/year, reaching their final size of 20 to 30 lb within a few years, and can live for 10 to 15 years. Unfortunately, when they reach maturity, their rate of weed consumption declines, and restocking of additional fish is required every 5 to 6 years. Grass carp have definite preferences on the type of vegetation they consume. They prefer tender, succulent vegetation that is under water. This makes them best suited for submerged vegetation, and they will not generally control tough, fibrous plants that grow up out of the water. The extent that they are able to control a particular weed depends upon many factors, including their feeding preferences, the aquatic plant density, water temperature and the number and size of grass carp stocked. As more preferred vegetation becomes scarce, grass carp will eat less preferred types of vegetation.

Even the water chemistry can affect weed palatability. If you feed your fish floating fish food, grass carp will consume it as well as aquatic plants. Grass carp are readily available in Ohio. Ohio permits the stocking of triploid (sterile) grass carp in ponds and lakes. If largemouth bass are present, the grass carp stocked should be 8 to 10 inches in length. The stocking rates can vary depending on the amount of weeds. A standard recommendation is 10 to 20 per acre, but if the pond has plant coverage of greater than 50%, a stocking rate of 20 or more per acre may be required. As a biological control agent, they may not provide immediate results. Often it will take a year before a plant problem is brought under control, assuming the offending plant is one that grass carp will readily consume.

If the pond/lake owner wants quicker results, applying an aquatic herbicide followed by stocking grass carp may be the best solution. Stocking should take place after much of the dead plant material has had a chance to decompose (2 to 3 weeks). Grass carp are natural inhabitants of rivers and readily escape ponds that overflow. Barriers on spillways are a good idea to prevent fish losses. After the grass carp reach maturity, the pond/lake owner may want to remove them. These large fish can be removed by snagging, bow fishing, spearing or angling. Their habit of hanging near the surface can make bow fishing especially simple. Because of their jumping ability, seining is often not effective. Their flesh is white, firm and not oily, but the muscle mass contains “Y” bones that can make cleaning more difficult. Their flesh is considered a delicacy by many seafood enthusiasts