Triploid Grass Carp Information

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Will Triploid Grass Carp Work for You?

Before deciding to stock grass carp, it's important to identify the vegetation you want to control. Grass carp have definite food preferences. Bushy pondweed, American pondweed, and hydrilla are preferred foods. Grass carp are not effective for control of bulrush, filamentous algae (pond scum or moss), water primrose, coontail, Eurasian milfoil, or cattails. If you're not sure what's growing in your pond, try the Pond Manager Diagnostics Tool provided by the Texas Cooperative Extension Service.

Triploid grass carp are inexpensive compared to most other aquatic vegetation control methods. Keep in mind, however, that the types of plants these fish prefer may also be important for sportfish habitat and waterfowl food. Aquatic vegetation can be important in maintaining good fish communities and providing food for other wildlife species. Stocking grass carp may also result in alga blooms and reduced water clarity.

Triploid grass carp:

• are sterile and will not reproduce.
• are only distantly related to the undesirable European carp, and share few of its habits.
• feed only on plants, not on fish eggs or young fishes.
• feed from the top of the plant downward; however, where all submersed vegetation has been eliminated, the water can become turbid as hungry fish eat the organic material out of the sediments.
• go dormant during the winter and resume intensive feeding when water temperatures reach 68°F.
• live for at least 10 years and probably longer in Texas waters.
• grow rapidly and may exceed 60 pounds.
• are difficult to catch with conventional fishing methods.

Stocking Guidelines

• The recommended stocking rate for triploid grass carp is five per acre if the water body has 50% or less plant coverage, and 10 per acre if plant coverage is greater than 50%. If warranted, the stocking rate can be increased with consent of your local TPWD fisheries management biologist.
• Triploid grass carp should be 10-12 inches long when stocked. Smaller carp are likely to be eaten by other fish.
• Early spring is a good time to stock. To enhance effectiveness of triploid grass carp, overabundant vegetation should first be reduced by winter die-off, herbicide treatment, or water-level drawdown to promote grazing on re-growth.
• If the water body is overstocked, all submersed aquatic plants may be eliminated. Removing excess fish can be difficult.
• If insufficient numbers of triploid grass carp are stocked, less-favored plants may become overabundant.
• Depending on plant types, plant density, and stocking rate, it may take several years to achieve control using triploid grass carp. Restocking, generally every 5 to 7 years, is needed for maximum effectiveness.

Obtaining a Permit

Before stocking, water body owners, their agents, or controlling authorities must obtain a Triploid Grass Carp Permit from the Inland Fisheries Division of the Texas Parks and Wildlife Department. To apply for a permit:

• Download the application form (PDF 116 KB) and instruction packet (PDF 305.6 KB)
• Or, call (512) 389-4444 or 1(800) 792-1112 to request an application packet by mail. The 800 number will get you to the main TPWD switchboard. When you hear the recording, select 4, then 4 on the next set of options.

Once the application has been received, it will be reviewed by a District Fisheries Management Biologist. In some cases, a TPWD staff member will contact you or make an on-site visit to ensure the fish will not escape into public waters. Allow 4 to 5 weeks for the entire permit process. Acceptance of your application is not guaranteed. Stocking of triploid grass carp is not allowed in some environmentally sensitive areas where threatened, endangered, or unique species occur.

After you receive an approved permit, triploid grass carp must be purchased from a commercial fish farmer who holds an Exotic Species Permit authorizing possession of triploid grass carp. A list of permitted fish farmers will be provided with your approved permit.

If you need additional fish, it will be necessary to apply for a new permit.

Preventing Escape

Triploid grass carp readily seek flowing water and often escape before controlling nuisance aquatic plants. Escapement of the stocked fish can reduce or eliminate their potential for plant control within targeted areas, and can threaten beneficial plants outside of targeted areas. Therefore, emigration barriers are required for many, and recommended for most, water bodies being stocked with triploid grass carp. Ensuring that triploid grass carp remain where they are stocked makes economic sense for the water body owner and helps protect beneficial aquatic vegetation in our public waters. In cases where emigration cannot be prevented, chemical or mechanical control of aquatic plants is recommended.

With few exceptions, the best screening device for nearly all outlet types is the horizontal parallel steel-bar design. The orientation of the bars allows unrestricted passage of small debris, thereby minimizing maintenance, clogging, and flooding concerns. Bar thickness of ¼- to ½- inch is preferred. Round bar stock will facilitate debris passage. For a spillway barrier (Figure 1), the horizontal bars are attached to vertical support posts (minimum ¾-inch diameter) spaced 4 feet apart. Horizontal bars should be spaced 2 inches apart. The barrier should span the entire spillway. Since triploid grass carp are excellent jumpers, barrier height should extend 2 feet above the normal high water level. For capping a drainage pipe (Figure 2), a similar bar design should be used. Extending the bars 4-5 feet above the overflow pipe allows water to rise over debris and begin flowing again should the screen become clogged.

Welded wire and chicken wire are not effective as barrier materials. These types of materials readily clog with debris and the force of even a small amount of water can destroy the barrier. Clogged barriers may threaten the integrity of dams.

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