sealPurdue News

April 1998

Fish farmers must learn zebra mussel prevention from A to Z

WEST LAFAYETTE, Ind. -- Looking forward to the 10th anniversary of the American debut of the zebra mussel and looking back at the tens of millions of dollars of damage the miniature mollusk has inflicted on industrial and municipal water users, it's no wonder aquaculture managers are wondering when it's their turn.

Illinois-Indiana Sea Grant aquaculture specialist LaDon Swann says "Anytime now."

The fingernail-sized mussel's ability to thrive in U.S. waters, its remarkable proclivity for proliferation, and its gift for hitchhiking in bilge water or on boat bottoms makes fish farm contamination a foregone conclusion, says Swann, who works out of Purdue University's animal sciences department. In response, Sea Grant has published a series of fact sheets to help aquaculturists prevent or control a zebra mussel infestation.

Commercial aquaculture operations, several of which operate in Illinois and Indiana, may be at risk, he says, because of the large amount of water that accompanies wild-caught fish, brood fish or fry stock that may be introduced to the operation. Undetected Zebra mussel larvae could be suspended in the water, Swann says, or the spat could be introduced though surface water supplies.

"Zebra mussels also can enter an operation through equipment such as nets, baskets and boots that have been used in infested areas," Swann says.

The problems start when the juvenile mollusks begin attaching to virtually any hard surface, including aerators, water supply valves and filtration systems. Because zebra mussels are filter feeders, they prefer settling in high-current areas which will bring a lot of food their way -- such as an intake pump.

Swann says the mussels pose two other potential problems: Some of their European ancestors harbor organisms that can cause diseases in fish, and their American offspring may, too. Also, a fish farm contaminated with zebra mussels could conceivably face quarantine measures or restrictions on where live fish could be shipped.

Because chemical controls can be expensive and could hurt other aquatic life forms including the farm fish, Swann recommends creating a prevention plan to head off zebra mussel infestation along with a monitoring program if an operator suspects that a pond may be affected.

"It's called a Zebra Mussel Critical Control Point Program, where operators identify the points of their operation that may be susceptible to zebra mussel introduction and put measures in place to avoid infestation," Swann says. "The fish farmers would also establish a scouting program for the pest and decide in advance what to do if they find any."

For example, operators may decide to thoroughly filter surface water supplies, steam-clean or ban outside nets, traps and other equipment, and insist on fry and fingerlings from zebra-mussel-free suppliers. They may also use a 1 percent salt solution during fish transport, which has been shown to control juvenile zebra mussels.

Zebra mussel control at the farm, though, is more difficult. Disinfectants such as iodine and calcium hypochlorite aren't completely effective, and stronger ones are toxic to fish. Some aquaculture operations may be able to drain entire ponds to kill off zebra mussels, and for them, Sea Grant researchers recommend a two-week drying out period in either very cold or very hot weather.

Many molluscicides haven't been approved for aquaculture use and may require special permission from state environmental agencies, Swann says.

In any case, zebra mussel control for aquaculturists promises to be more difficult and costly than prevention.

A comprehensive guide to zebra mussel monitoring, Biological Notes 138, by Sea Grant researcher J. Ellen Marsden is available for $3 from the Illinois Natural History Survey at (217) 333-6880. The free publication "What Every Fish Farmer Should Know About the Zebra Mussel" is available from Mississippi Sea Grant at (601) 388-4710.

CONTACT: Swann, (765) 494-6264; e-mail,

Purdue News Service: (765) 494-2096; e-mail,

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