Triploid Grass Carp: The Living Lawn Mower

By Bob Wattendorf and Dave Eggeman

florida fishing
Grass carp were brought into the US in 1963 as a possible bio-control for aquatic plants but controversy over how they would impact native plant and wildlife communities ensued.

?Grass carp wars? that's what it was called in the 1970's when the controversial proposal of importing fertile grass carp from Asia to control non-native aquatic plants came to Florida. Maybe calling it war was overkill, but the two sides certainly were polarized. The thing was--both sides had good intents and cause for concern. So why the controversy, and 40 years later, what is the outcome?

Florida's temperate to subtropical climate makes it ripe for introductions of plants and wildlife from similar climates. Non-native species often do exceptionally well when placed in a new environment, with few predators, parasites or diseases that have adapted to control them.

Water lettuce from South America was introduced to Florida in the 1500?s. The even more problematic water hyacinth gained a foothold in the 1880s. A variety of chemicals including railroad cars full of sulfuric or hydrochloric acid were experimented with as possible controls in the early 1900s. When dumped in rivers, the acid flowed along the bottom killing the plants, but you can imagine the collateral damage done to fragile ecosystems. Such efforts were shortlived, as researchers sought better solutions. By the mid-1900s new herbicides were being discovered. Early experimental chemicals often had undesirable effects on animals and frequently killed desirable plants, making them controversial. By the late 1900s things were changing. The DDT crises exposed by Rachel Carson in ?Silent Spring? lead to more thorough and cautious review, labelling and application of herbicides and pesticides.

florida fishing
Hydrilla and other non-native plants can take up virtually the entire water column causing navigation and other problems.

About that time, Florida was experiencing problems with maintaining healthy native aquatic plant populations. Stabilizing water levels to ensure adequate potable and irrigation supplies and prevent flooding vastly altered the aquatic landscape. Into this altered environment came hydrilla, an exotic plant from India. Although it provides good habitat for fish and waterfowl, it also can block water flow causing flooding, preventing navigation for boaters and detracting from other important uses of rivers and lakes.

Lack of aquatic plants can be a major environmental problem. Florida's outstanding freshwater fisheries and many wildlife populations are heavily dependent on natural aquatic vegetation. Rooted aquatic plants provide benefits such as: stabilizing shorelines, preventing erosion, reducing turbidity (muddy water), providing cover for fish to hide from predators, serving as food for insects that in turn are consumed by fish, using nutrients that reduce algae blooms, protecting fish eggs from currents, providing shade and cover for fish, and serving as a visible feature to help anglers locate sportfish.

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Cookie cutters and other mechanical equipment to remove plants are costly and can injure fish and wildlife.

So when proposals to stock open water bodies with fertile grass carp (white amur; Ctenopharygodon idella) that spawn in similar habitats to striped bass were proposed, fisheries biologists were concerned these Asian carps would get out of control and wreak havoc on native plant and fish communities. Apprehensions that such spawning could occur have been borne out in the Mississippi and Missouri rivers where Asian carp reproduction is having significant effects. Thus far, in Florida, thanks in part to the diligence of management agencies, there are no documented cases of grass carp spawning in the wild. However, recently FWC biologists determined that a few diploid escapees from flooding in bordering states made it to the Suwannee River causing concern that only triploid grass carp should be used.

Florida helped lead the way with research on grass carp food habits and with creating triploid (functionally sterile) grass carp. Florida biologists also created the certification program using a Coulter Counter to check the nuclear volume of grass carp red blood cells rapidly and efficiently that the U.S. Fish and Wildlife Service and state agencies still use to ensure only triploid grass carp are stocked. However, even with sterile fish, if too many grass carp are stocked and plants are eliminated, the problem may last as long as the fish are alive or longer--and that can be over 15 years.

Consequently, legitimate concerns existed back in the 1970s and ?80 and a full gamut of options for aquatic plant management were considered. About that time, the Game and Fresh Water Fish Commission (now Florida Fish and Wildlife Conservation Commission (FWC)), which had operated their own spray crews to control invasive aquatic plants, relinguished the program to the Department of Natural Resources (now Department of Environmental Protection). In 2008, the FWC participated in ?A Risk Analysis Pertaining to Use of Triploid Grass Carp for Biological Control of Aquatic Plants? ( The review concluded that in public waters agencies should develop management plans for each stocking. The safest approach includes initial herbicide treatment followed by a low level stocking of grass carp.

In 2008, the legislature moved the Invasive Plant Management Section back to the FWC. The Section subsequently initiated a public review process to create a new ?Agency Position on Hydrilla Management? (Go to for more details). The position recognizes that native aquatic plant communities provide ecological functions to support diverse fish and wildlife populations. Hydrilla is an invasive, non-native plant that requires management. However, in water bodies where hydrilla is established, FWC will manage it in ways commensurate with the primary use of the waterbody. Plans will incorporate public input, be adaptive and reflect local conditions.

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Therefore, 40 years later the grass carp wars have come to a truce. In the interim, scientifists conducted a vast array of experiments in laboratories and controlled pond settings, and evaluated practical management programs in large lakes across the southeastern United States. That knowledge lead to a meaningful risk assessment for triploid grass carp and new position on how to manage hydrilla.

There are still multiple ways of addressing aquatic plant concerns and each has a role, as well as pros and cons. Chemical control is expensive (up to $750 per acre per year). Mechanical control is even more so--about twice as costly as chemical control and can disrupt fisheries and spread plants. Biological controls using insects or diseases have not proven suitable for manageing hydrilla, leaving triploid grass carp as the most effective biocontrol.

These fish can control certain aquatic plants in moderate-sized lakes at a cost of $20 to $250 per acre. In private ponds, golf course ponds, irrigation ditches and similar locations, where sport fishing is not the primary activity, they provide an environmentally sound, cost-effective way of controlling aquatic plants. Such stockings require a permit from the FWC. The Invasive Plant Management Section issues nearly 1,500 such permits annually saving users money and reducing herbicide use (click here for more details).

Section personnel also plan and monitor stocking triploids in public waters (ca. 100 at the current time). In situations where sport fisheries are important, the fish is not a panacea. If triploid grass carp eat too many plants, important habitat is destroyed, and sport fish can be adversely affected. Since triploids school together, they often impact plants in areas not heavily utilized by people and avoid congested areas where plant control is most important to boaters.

florida fishing
Triploid grass carp live as long as 15 years and frequently exceed 30 pounds.

In conclusion, FWC uses a permit program to allow citizens to purchase and stock triploid grass carp as a cost-effective means of controlling plants in private waters. The FWC also saves the state money by using the fish prudently in public water bodies to reduce the need for expensive chemicals, but draws the line at stocking triploid grass carp in large open systems where the fish are unpredictable and could negatively impact the state's immensely valuable sport fisheries and the delicate balance of our natural ecosystems.

Instant licenses are available at or by calling 1-888-FISH-FLORIDA (347-4356). Report violators by calling *FWC or #FWC on your cell, or 1888-404-3922. Visit for more Fish Busters' columns.

For more environmentally-related news, click here.

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