Florida’s biological crapshoot with carp : State introduces fish to control canal weeds. But past use of exotics shows such a cure can be worse than the disease.

MIAMI — Soon after the Overturfs pulled the truck alongside the canal to end their 24-hour drive from Arkansas, the fish were flying. Beverly hooked an 8-inch hose up to a tank, Chuck hoisted the hose onto his shoulder like a bazooka, told Beverly “go” and suddenly it was raining carp.

This wasn’t shooting fish in a barrel; it was more like fish barreling through a chute. The silver-sided 10-inchers splattered into the warm waters of the C-100 canal, righted themselves, formed schools, then swam off to explore their new home--a vast system of waterways that provide flood control and make dry-land living possible in South Florida.

“They probably won’t start eating right away,” says biologist Gordon Baker, overseeing the operation for the South Florida Water Management District. “But they will.”

They’d better. The 5,000 grass carp on the Overturfs’ truck were the first of 21,000 dumped into the canals here last month in an effort to eradicate exotic weeds. Grass carp are known as voracious consumers of aquatic vegetation, especially hydrilla and other unwanted species that are impeding the flow of water and fouling floodgates.

The idea of spending about $80,000 to introduce yet another exotic animal into the fertile South Florida ecosystem--already alive with a Noah’s Ark of foreign critters, most of them unwelcome--may seem imprudent. After all, accidental introductions have resulted in thriving populations of pests, such as the African giant snail, the cane toad, monk parakeet, various lizards and the fire ant, among many others.

At least 19 nonnative fresh-water fish already swim in Florida’s canals, rivers and lakes, according to the federal Office of Technology Assessment.

Indeed, the fish branded Florida’s most troublesome, the blue tilapia, was introduced by the state’s Game and Fresh Water Fish Commission as a sport fish and weed-eater. But it proved to be unpopular with anglers, to have an anemic appetite and has multiplied so mightily that it now competes with native species.

“It is ironic to chase one exotic with another, but that’s what we’re faced with,” says Don C. Schmitz, a biologist with Florida’s Department of Environmental Protection. “We want to make sure we don’t unleash a new ecological disaster, but if we can find a good biological control agent, we have to use it.”

Baker says the grass carp is a good agent, in part because the fish are sterile. As raised by J. M. Malone & Son, a Lonoke, Ark., fish farm, these white amur carp, native to the rivers of Russia and China, are genetically engineered to have an extra set of chromosomes through a process in which fertilized eggs are shocked with a jet of water.

These carp are created, says Baker, to eat weeds and die.

Since the hybrid was produced in 1983, the grass carp has been introduced into the water districts in Southern California’s Imperial and Coachella valleys, the Panama Canal and the Nile River in Egypt, said Doretta Malone, the fish farm proprietor. “Ten to 12 fish per acre will clean up and control the worst aquatic vegetation,” Malone says. “And a fish will eat for five to seven years, and grow to 80 pounds or more, before it gets old and lazy.”

If the carp proves successful in South Florida, the Water Management District plans to restock the fish at a rate of about 10% a year, to replace those that become alligator food or die in other ways. Life expectancy is about 10 years.

Dan Thayer, director of vegetation management for the water district, admits the carp come with some risks. Once they eat all the exotic plants, they could begin to dine on eel grass and other natives favored by manatees. And they could get into the Everglades ecosystem and further rock the balance of nature there.

Malone predicts the grass carp will win friends in South Florida. “They are fast swimmers, and they will play and roll over like a porpoise,” she says. “Working with this fish all these years, I can see that they have an intelligence that other species don’t have. I see it in their eyes. They will respond to you. And they are also weather forecasters. They are very active when a front is coming through.”

Baker is more concerned about the carp’s taste for hydrilla and East Indian hygrophila. If the fish does not attack the weeds, Baker says, water managers would have to use herbicides, “and that’s a last resort.”

Another concern is human taste for the carp. Fishing magazines, Baker reports, have written about ways to catch the fish, and recently a Chinese-language newspaper in South Florida printed a recipe for steamed carp in a wine, soy and ginger root sauce.

Baker reminds anglers that taking the carp from the canals is illegal. And besides, “those fish are designed to eat vegetation and keep the water flowing.”

“So people have to decide: They can either eat dinner or have a clean canal. Please, put them back.”