Officials Say Still Many Unknowns About Crawfish White Spot Disease

Charles Lutz, Shirley, Mark G., Schultz, Bruce  |  5/31/2007 6:08:58 PM

News Release Distributed 05/25/07

KAPLAN – Crawfish producers learned at a meeting on May 23 that investigators have few answers to questions about how the White Spot Syndrome Virus infected four crawfish ponds in South Louisiana.

Officials from several agencies said they have yet to come up with a key factor.

“We haven’t found a common thread yet,” said Scott DeJean, a veterinarian from the U.S. Department of Agriculture. He spoke at a meeting called by the LSU AgCenter to respond to producer questions about the virus.

Two ponds are in Vermilion Parish, and St. Martin and St. Landry parishes each have one affected pond. All have been quarantined. Nine other ponds have suspicious signs but the virus has not been confirmed in those, DeJean said. Testing on crawfish samples from those ponds should be completed soon.

Dr. Greg Lutz, LSU AgCenter aquaculture specialist, said shrimp farms in Texas and overseas have been dealing with the virus for years, starting in 1992-93 in Asia, but it was only recently detected in Louisiana crawfish.

It is found in Gulf of Mexico shrimp and crabs, he said. “A good portion of the imported shrimp we eat in this country carries this virus.”

But, he said, this is the first time the virus has been known to affect pond crawfish in Louisiana.

“This is all new to us,” Lutz said. “We haven’t ever seen anything like this in crawfish.”

The virus survives freezing temperatures. A virus, unlike bacteria, cannot be treated with a chemical, he said.

Experts have agreed that humans are not affected by the virus, but it could have a serious impact on the Louisiana crawfish industry.

Symptoms of the disease include crawfish that are lethargic and weak and often they cannot walk. Dead crawfish are often found in traps and on the edges of ponds. Crawfish do not develop the conspicuous white spots found in affected shrimp.

The LSU AgCenter is recommending producers avoid unnecessary restocking of permanent ponds. Researchers say supplemental stocking of new crawfish is often unnecessary.

The AgCenter also recommends using only a single source of healthy crawfish for the time being instead of using several suppliers, which would normally be recommended.

To prevent possibly transferring the disease to other ponds, the AgCenter is recommending producers not move traps, boats or other equipment from farm to farm. And if a problem is suspected, researchers have recommended keeping equipment confined to one pond. Before moving boats or traps to another pond, they are recommending washing to remove mud and debris, then spraying with a 5 percent bleach solution.

Dr. Henry Moreau, state veterinarian for the Louisiana Department of Agriculture and Forestry, said ponds in a 1-mile radius around affected ponds will also be tested.

“We’re trying to do the things to keep you in business and possibly control this virus,” Moreau said.

Mark Shirley, LSU AgCenter fisheries agent based in Vermilion Parish, told producers keeping good records of their work might help researchers pin down how the disease spreads. He said crawfish in ponds adjacent to affected ponds, even those linked by canals or pipes, don’t show any symptoms.

Shirley urged producers to continuously monitor the oxygen levels of their ponds to make sure low oxygen is not causing crawfish mortality.

For more extensive information on the disease, go to this LSU AgCenter Web site and click on “Crawfish White Spot FAQ.”

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Contact: Dr. Greg Lutz at (225) 765-2848, or Glutz@agcenter.lsu.edu

Mark Shirley at (337) 898-4335 or MShirley@agcenter.lsu.edu

Writer: Bruce Schultz at (337) 788-8821 or BSchultz@agcenter.lsu.edu

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