By Rebekah Ray
Delta Research and Extension Center

STONEVILLE – A serious disease is threatening some species of freshwater fish, and although it has not been found in Mississippi, it is a concern for catfish producers when they want to move live catfish across state lines.

Viral hemorrhagic septicemia affects freshwater and marine species including food fish like trout, flounder, herring, salmon, halibut, sea bass, cod, perch and shad. The highly contagious disease occurs primarily in bodies of water with temperatures ranging between 48 degrees and 64 degrees. Recent Mississippi catfish pond temperature averages ranged between 50 degrees and 88 degrees.

Symptoms of viral hemorrhagic septicemia, or VHS, include bloated abdomens, internal and external hemorrhaging, erratic swimming, bulging eyes and rapid die-offs. Not all fish infected with VHS die or exhibit symptoms; many can become carriers. Transmission occurs through urine and reproductive fluids, wounds, gills or predation on infected fish. Fish-eating birds also can carry the disease. The virus does not affect humans, even if they eat infected fish.

“Channel catfish are on the U.S. Department of Agriculture’s list of VHS-susceptible fish species. However, this is mainly a cold-water viral disease that has not been identified in our area,” said Lester Khoo, director of the Aquatic Diagnostic Laboratory at the Thad Cochran National Warmwater Aquaculture Center in Stoneville. “Most warm-water fish have been resistant to VHS.”

Researchers at the aquaculture center have been collecting data on farmed fish to help establish a certification program that will enable Mississippi farmers to ship live, pond-raised catfish to states that have VHS testing requirements, Khoo said.

“The likelihood of finding the virus in Mississippi is very small. Freshwater cases have been mainly in the Great Lakes region,” Khoo said.

VHS is a reportable disease, meaning that it must be reported to both the state veterinarian and the USDA area veterinarian-in-charge.

“The disease is diagnosed using virus isolation techniques of cell cultures. Those cultures that test positive are sent to USDA’s National Veterinary Service Laboratories in Iowa for confirmation,” Khoo said.

The USDA laboratory then relays confirmed positive reports to the state and federal veterinarians.

Mississippi produces more than 60 percent of the nation’s farm-raised catfish. In 2008, the value of the state’s catfish industry totaled $258 million.

“Even though VHS does not occur in Mississippi, the disease reporting requirements have impacted the catfish industry by preventing shipment across state lines,” said Dr. Jim Watson, Mississippi’s state veterinarian and head of the Mississippi Board of Animal Health. “Some states require VHS testing before allowing fish to be brought into that state.”

If the disease is found in a river’s watershed that includes Mississippi, the state’s catfish industry would be negatively affected by losing the ability to move live fish across state lines. A VHS certification program could help alleviate some of those concerns, Watson said.

The certification program is voluntary and is a joint effort between catfish farmers, MSU, the Mississippi Board of Animal Health and USDA. Currently, testing is free to the farmer. Participating in the program allows farmers with negative tests to move live fish across state lines. It also develops surveillance data to establish the disease-free status of the state’s catfish industry.

To participate in the testing program, contact Khoo at (662) 686-3305 or khoo@cvm.msstate.edu.