Using Grass Carp to Control Weeds in Alabama Ponds 3 Populations

ALABAMA A&M AND AUBURN UNIVERSITIES Using Grass Carp to Control Weeds ANR-452 in Alabama Ponds

Controlling Figure 1. Grass carp or white amur vegetation in ponds (Ctenopharyngodon idella) is critical to good management. Too much vegetation amur (Ctenopharyngodon idella) plants with small leaves are rou- interferes with fishing, swim- is one of the best and most com- tinely eaten by grass carp. When ming, and boating. Nutrients monly used biological control stocked at high densities, grass that could be stimulating algae, agents used in ponds (Figure 1). carp will sometimes control less which effectively support fish This large minnow is native to preferred vegetation as they production, are used by weedy large rivers in Russia and China. eliminate other more attractive plants. Thick beds of weeds can It was imported into the United types. cause oxygen depletion, leading States in 1963 for aquatic weed Grass carp are native to to fish kills. Weeds also interfere control and as a food prod- large rivers in Asia and require with feeding by largemouth bass, uct. Unlike the common carp flowing water to reproduce. reducing their growth rate. In (Cyprinus carpio), which is also It is unlikely that they would large reservoirs, about 20 per- native to Asia, grass carp do even release eggs in the stand- cent weed coverage has a posi- not muddy the water of ponds ing water of a pond, but, if they tive effect on fish reproduction by feeding in the sediment. As did, the eggs would sink to the and growth. Because ponds are their name implies, grass carp bottom and suffocate. While the shallow, the presence of a few eat vegetation. They can eat two many dams on Alabama’s major weeds can quickly turn into an to three times their own weight overgrowth of plants. in aquatic plants each day, and Table 1. Weed management involves they can gain 5 to 10 pounds several techniques. It is often in a single year. When prop- Tips for Preventing tempting to seek a quick fix erly stocked in ponds, the grass Weed Infestation to any weed problem. While carp can control many problem herbicides may seem to be the weeds, but they cannot control • Build ponds with edges that drop high tech answer, they should all weeds. The grass carp’s soft, quickly to 3 feet in depth. be the last choice if less expen- fleshy lips and no teeth prevent sive, more long-lasting methods it from biting off chunks of veg- • Practice good fertilization techniques. fail. First work to prevent weed etation the way a horse would infestations (Table 1) and, if nec- crop off grass (Figure 2). Instead, • Be careful not to introduce weeds to essary, use biological methods grass carp must suck weeds the pond (boat trailers, aquariums, to provide long-lasting, environ- into their throats where they aquatic gardens, etc.). mentally friendly control. grind the material with tough, The grass carp or white bony plates. Only soft-stemmed www.aces.edu rivers may have resulted in the decline of some of our native fishes, these same dams may also have prevented grass carp from reproducing in the wild. The still waters of reservoirs may have killed the eggs of the grass carp. In the upper Mississippi River and the Missouri River, grass carp have established reproducing populations in the wild. These fish have destroyed many native plant beds in these rivers. Voracious grass carp are capable of doing great damage to wetlands. It is this concern that has led most states to pass laws dictating strict control of Figure 2. The mouth of a grass carp. Notice the lack of teeth. the stocking of grass carp. These states require a permit for the by constructing a barrier or fish It is better to lose grass carp out possession of grass carp and fence across the spillway. This the spillway than to risk having certification that all grass carp barrier should be constructed water go over the crest of the stocked be sterile triploids. with approximately 1-inch spaces dam causing the structure to fail. between horizontal bars (Figure When stocked at recom- Control Methods 3). Construction of this type will mended rates, grass carp do not reduce the amount of debris that Because the grass carp is interfere with other fishes nor do collects on the barrier although a fish native to large rivers, it they interfere with angling. Grass sticks, leaves, and other material is attracted to flowing water. carp themselves are one of the can still cause clogging. When During periods of high flow, top four most cultured fish spe- clogged, water will back up and grass carp will leave a pond cies in the world. They can be flow over the top of the barrier. through the emergency spillway. caught with some difficulty on For this reason, never build the This problem can be reduced a hook and line using worms, barrier to the height of the dam. grass, catfish pellets, or small

Table 2. Pond Plants and Potential Control With Grass Carp Species of Plant Stocking Recommendation

Easily controlled hydrilla, elodea, najias, bladderwort, egeria, Stock at standard rate. Control is usually within one season potomogeton except with severe problems.

Controlled with watermilfoil (parrot feather, eurasian, watermilfoil, etc.), slender spikerush, duckweed, red Stock at 1 to 2 times standard rate. Control may take more difficulty ludwigia than one season.

Controlled with filamentous algae (lyngbya, Pitophora, Stock at 25 to 50 per acre. extreme stocking rates etc.)

Not usually controlled cattails, alligator weed, watermeal, water- Use other control measures and stock grass carp at standard shield, American lotus, waterlillies, willow, rates. Grass carp will help prevent other weeds from replacing with grass carp water primrose, water lettuce, water hyacinth these, plus they will sometimes suppress growth of even these resistant forms by eating the young shoots.

2 Alabama Cooperative Extension System 4 - inch creosoted year. For a list of producers in post ¾ inch your area, contact your county 48 round inches 1 inch Alabama Cooperative Extension bar between bars System agent. Grass carp are sold by com- mercial fish dealers across Alabama. It is a federal offense to violate state laws that prohibit

20 feet the possession, transportation, or ¾ inch ¼ x 2 x 4 inch sale of grass carp. Many states round bar flat bar require special permits to pos- Figure 3. The spillway barrier should be firmly anchored using steel or creosoted wood sess or transport this fish. Most posts in concrete. states, including Florida, Georgia, and Tennessee, require that grass dough balls as bait. Grass carp when cutting through the meat, carp be certified sterile triploids. have small bones in their flesh angle away from the bone to Fertile grass carp are not illegal that can be removed by proper avoid cutting it. After cooking, in Alabama and can, therefore, dressing. Their firm and flaky the steaks or fillets can be bro- be used freely. Before trans- flesh has a good flavor. Grass ken to expose any bones. Grass porting grass carp across state carp can be prepared as either carp is suitable for any recipe lines, check with the natural fillets or steaks. When prepared calling for firm, white, flaky fish. resource agencies in all the as steaks, the bones are left in This includes grilling, frying like states you will be crossing the meat while cooking (Figure catfish, or more exotic approach- to determine the legality of 4). When filleted, y-shaped es such as gumbos, court bouil- transporting the fish through bones extend along the length lon, or Asian curry. Grass carp their state. of the fish into the meat. Don’t are especially good smoked. chop grass carp the way you Sizes and Numbers would a boneless fillet because Sources of Grass Carp to Stock this would break the bones into Adult grass carp spawn Table 3 provides recom- many difficult to remove pieces. in late spring when the water mended grass carp stocking sizes Use a sharp knife to carefully is warming. Hormone injec- and rates for use in ponds. Stock cut the flesh into portion-sized tions force spawning. All sizes larger grass carp (8 to 10 inches) pieces. When you feel resistance are available at any time of the in ponds with established bass

Grass Carp Marinade for smoked and grilled steaks and filets

1 quart water Salt (¼ cup for smoked carp; 3 tablespoons for grilling carp) 2 tablespoons soy sauce ½ teaspoon lemon or lime juice Your favorite spices (onion, garlic, pepper, etc.) to taste

For grilled grass carp: Cover fillets or steaks with mixture for 8 to 12 hours in refrigerator. Grill at high heat until flaky.

For smoked grass carp: Smoke fillets or steaks using indirect heat (180 degrees F) for at least 4 hours until flaky.

The cooked fish can be eaten immediately or used cold in salads and even paté.

Figure 4. Grass carp steaks are suitable for grilling.

Using Grass Carp to Control Weeds in Alabama Ponds 3 populations. Stock smaller fin- Table 3. gerlings (2 to 6 inches) only Recommended Stocking Rates Per Acre for Grass Carp where no predators exist or in newly stocked ponds where the Degree of Weed Infestation predators are about the same Bass situation Slight Moderate Heavy size as the grass carp. Smaller Ponds with bass: stock large carp, 8 5/A 10 to 15/A 15 to 50/A fingerlings can also be stocked to 12 inches in catfish ponds. Grass carp are readily eaten by bass and other Ponds without bass: stock small 6 to 8/A 12 to 18/A 18 to 50/A predatory fishes. carp, 2 to 6 inches

Expected Weed not have enough food. The fish Large grass carp will injure Control Results can be selectively harvested by fingerling catfish by thrashing It takes time for grass carp angling, by using a large mesh and jumping in the harvesting to bring a weed problem under gill net, by applying 0.10 part seines. Workers who harvest control. Weeds may or may per million 5 percent rotenone, catfish in ponds stocked with not be controlled by the end or by shooting them with a bow grass carp can also be injured of the first growing season. If and arrow. While grass carp are from jumping grass carp. Make weeds continue to flourish dur- excellent table fare, it is gener- workers aware of this potential ing the second year, then stock ally not advisable to eat fish danger. more grass carp. You may need killed with rotenone. to restock with enough fish to The material in this publication is bring the total number in the Stocking Grass Carp partially adapted from the following: pond up to the maximum nor- in Catfish Production Brunson, M. 2002. Aquatic Weed mal recommended rate of 20 fish Ponds Control: Using Grass Carp. Information per acre. For control of difficult Grass carp can also be used Sheet 1556. Extension Service of Mississippi State University. weeds, you may need to use for weed control in catfish pro- herbicides to reduce the prob- duction ponds. They will eat Sutton, D. L. and V. V. Vandiver Jr., lem. Then rely on grass carp to some of the catfish feed, but, 1986. Grass carp, a fish for biologi- maintain control. when stocked at recommended cal management of hydrilla and other aquatic weeds in Florida. Bulletin If the weed you want to rates, they will not reduce catfish control is not a favorite of the 867, University of Florida, Agricultural production. Experiment Station. grass carp, you may need to Grass carp are in the catfish try other control methods. For ponds only a short time before Jensen, J. J. Spillway barriers for more information, see Extension the catfish are harvested so more farm ponds. Publication ANR-326, publication ANR-48, "Weed Alabama Cooperative Extension grass carp may be needed to System, Alabama A&M and Auburn Management in Lakes and control weeds in the ponds. If Universities, Alabama. Ponds." the catfish ponds are harvested After the weeds are gone annually, stock 40 to 50 8-inch Jensen, J. J. Using grass carp for controlling weeds in Alabama in ponds that are stocked at the fish per acre. Weed control in maximum rate, about half of the ponds. Publication ANR-452. catfish fingerling ponds may Alabama Cooperative Extension grass carp can be removed. If require stocking 50 to 100 8-inch System. Alabama A&M and Auburn the grass carp are left in these grass carp per acre. Universities, Alabama. ponds, the remaining fish will

Russell A. Wright, Extension Specialist, Associate Professor, Fisheries and Allied Aquacultures, Auburn University, and Claude Reeves, Extension Aquaculturist, Wiregrass Regional Research and Extension Center For more information, call your county Extension office. Look in your telephone directory under your county’s name to find the number. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.