Carrollwood Village enlists weed-eating fish to unclog retention ponds
They are genetically-altered vegetarians that can't reproduce and for years have kept invasive aquatic plants in check in Florida's inland waters.
Triploid Grass Carp were imported to the state decades ago to munch on troublesome vegetation that has clogged retention ponds and kept them from draining properly.
In this northwestern Hillsborough County enclave, community leaders recently restocked a vast system of manmade ponds with more than 1,000 of the aquatic lawn mowers.
"So far, they're doing a hell of a job," says Dan Ruskiewicz, property manager for several Carrollwood Village Homeowners' Associations. "We only put them in a couple months ago."
Ruskiewicz said the Carrollwood Village's board of directors decided last year to restock the ponds to begin controlling weeds that virtually have taken over some of the ponds.
He said the boards didn't want to use pesticides to remove the pesky aquatic plants.
"What we're trying to get away from is the use of chemicals," he said.
The ponds were stocked with grass carp years ago, Ruskiewicz said, but the population dwindled as the fish reached the end of their typical 10- to 15-year life cycle.
He said a decision by the board a couple of years ago to remove wire-mesh screening that kept the fish from migrating into other ponds also likely played a role in the depleted stocks.
The community's boards decided to remove the mesh screening because it had become clogged and was causing flooding problems in the neighborhood, Ruskiewicz said.
"There's some left, but many others probably got away into Brushy Creek," he said.
Poaching also has contributed to the decline, though to a lesser degree.
While Carrollwood Village residents are allowed to catch the fish in the ponds using a rod and reel, Ruskiewicz said, poachers have been caught using throw nets to get bait fish.
"Most of our residents just catch them and throw them back in," Ruskiewicz said.
The state has been working with grass carp for more than two decades, and since the 1980s has deployed millions in private and public lakes to keep down vegetation.
Michael Sowinski, a biologist with the Florida Fish and Wildlife Conservation Commission, said the grass carp prefers 10 plant species, but especially is fond of hydrilla, an exotic underwater plant common in Florida and widespread in the Carrollwood Village ponds.
He said grass carp also will eat duckweed and certain kinds of seasonal freshwater algae, which has been a major problem in the Carrollwood ponds in the past year.
"Algae is not their favorite food, but they'll eat it," he said.
Sterile fish, called triploids because they have an extra chromosome, are created when fertilized fish eggs are subjected to a temperature or pressure shock, Sowinski said.
By altering the species so that it cannot reproduce, he said, ponds, lakes and other bodies of water do not get so overpopulated that the grass carp starve to death.
To restock the ponds, a permit is required and the fish must be purchased and released by a company licensed by the state. State officials monitor the release of the grass carp.
To prevent stocked grass carp from migrating out of the ponds and into creeks, streams and rivers, all inlets and outlets to the ponds or lakes must be screened, Sowinski said.
"If you're paying $10 to $15 a fish, you don't want them going to work in someone else's pond or lake," he said.
Once grass carp are stocked, it might take years for them to control nuisance plants. Survival rates of the fish vary depending on factors such as presence of otters, birds of prey, or fish disease. A pond probably will need restocking about every 10 years.
Ruskiewicz said the carp already are making a difference in Carrollwood's ponds.
"They're doing a really good job," he said. "I can notice a change already."
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