Triploid Grass carp are legal in Oklahoma and require no permit. The grass carp is a different species from the common carp and can be distinguished by its cylindrical body shape, mouth at the tip of its head, lack of barbells (whiskers), and a lack of saw-toothed spines on its dorsal and anal fins. These fish are voracious plant eaters, consuming up to three times their weight a day in plants. The state record grass carp is almost 69 pounds. However, in most ponds grass carp probably won’t exceed 20 to 30 pounds.
Grass carp also are sold in hybrid and triploid forms. The hybrid has proven ineffective for controlling vegetation. The triploid is functionally sterile and is the only grass carp permitted in many states. This is why it is only legal to stock the Triploid Grass carp in Oklahoma, by using triploid grass carp, the pond owner is ensuring that the escape of fish into receiving streams will not result in reproduction in the wild.
Screens and other barriers are required to prevent the escape of grass carp; even a trickle of water is enough to allow escape. The cost of a screen is minimal when considering the cost of continually restocking to replace escaped fish (see Pond Construction, page 5, and Additional Information, page 42, for barrier construction information).
Grass carp will control most common pond weeds, although their feeding preferences change as they grow. Because larger grass carp do not eat filamentous algae, to control this plant small grass carp must be stocked.
In waters without predators (bass), stock grass carp no smaller than four inches. In waters with bass 10 to 12 inches long, small grass carp are a preferred forage. Reportedly they don’t avoid predation by bass and are easily eliminated. Grass carp larger than eight inches are worth the added expense in such situations.
Stock grass carp in lightly infested ponds at a rate of five to 15 per acre. In ponds larger than three acres, stock at 10 to 15 per acre. In heavily weeded ponds, stock 15 to 30 per acre. To control filamentous algae, stock 30 to 60 per acre using smaller grass carp. To eradicate vegetation in aquaculture ponds, stock as many as 40 to 80 per acre.
In most cases, control with grass carp occurs in the second year after stocking when the fish reach three to five pounds. An increased stocking rate will provide quicker results. Stocking grass carp after using an aquatic herbicide also should be effective. Restock grass carp as vegetation reappears in five to seven years or earlier.
Once the desired control is achieved, some grass carp may need to be removed. They can be caught on hook-and-line using dough balls or catfish chow; they also can be shot with a bow and arrow. Grass carp make fish table fare with their firm, white flesh and excellent flavor. However, proper preparation includes removing or otherwise handling small bones in the flesh.
Overstocking grass carp may lead to complete eradication of vegetation. This usually increases pond turbidity and lowers fishing quality. Be patient after stocking grass carp as it often takes one to two years before major vegetation reduction is noticed. For a list of grass carp suppliers, please visit the Oklahoma Department of Agriculture, Food & Forestry's aquaculture page at: https://ag.ok.gov/