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Controlling Pond Vegetation with Fish

There are no fish native to the United States that take care of aquatic weed problems in our ponds. If there were, we’d all have pristine ponds. Since that isn’t the case, you may to add non-native fish to do the job.

Todd Sink is an aquaculture and fisheries specialist with Texas Agrilife Extension. He says tilapia and grass carp are often used for weed control.

"If it’s a submerged vegetation, grass carp are the way to go," says Sink. "But if it’s floating vegetation such as duckweed or watermeal, grass carp will eat some of it, but tilapia can be more effective than grass carp at doing that."

Because they’re non-native species, you will need a permit to stock triploid grass carp or tilapia depending on the state you live in. Did you know there are 300 species of tilapia? Some states only allow the use of a few of those species, and others ban all tilapia in farm ponds to prevent them from becoming invasive in U.S. waters.

Sink says you can’t expect a fish to be the sole savior of a weed-infested pond. It’s just one of the tools in an integrated pest management plan.

"First you would go in with an appropriate FDA-approved aquatic herbicide and knock the population of that plant back really well, and you stock your grass carp or tilapia afterwards," he says. "And what they do is they clean up anything that you miss, or any regrowth or regeneration, and that actually gives you a much, much better management plan and control strategy for that vegetation."

It may take grass carp 2-3 years of munching before you see good results. Tilapia can get their work done in one season if they’re stocked early. But if not, you’ll have to restock them again the next spring because they die off when water temperatures dip below 50-degrees.

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