Don't Let ESC Stand in the Way of Higher Profits

Early Detection and Well Timed Treatment Prevent Losses

With more than 60 percent of all catfish operations reporting enteric septicemia (ESC) outbreaks, according to USDA's National Animal Health Monitoring System data, and losses exceeding $13 million, ESC tops the disease list for pond-raised channel catfish.

Since its discovery in 1976, ESC has moved from a virtually unknown disease to a full-blown threat to all levels of catfish production.

"Today ESC accounts for the majority of catfish death due to bacterial disease," confirms Dr. Patricia Gaunt, associate professor, aquatic animal health, Mississippi State University College of Veterinary Medicine.

Understanding ESC

ESC is caused by the gram-negative bacterium, Edwardsiella ictaluri, which attacks catfish when environmental conditions are favorable. Once thought to survive only a short time in water, research has shown it can survive up to 95 days in sterile pond mud at 25°C or 77°F.

According to Gaunt, most catfish farmers view ESC as a seasonal disease most typically striking for a couple of months during spring and fall—but that's changing as well.

"We're seeing more cases of ESC during the summer months outside the temperature window of 20° -28°C (68° -82°F)," stresses Gaunt. "The disease is definitely becoming less seasonal and now has at least a six-month season from May through October."

Another important factor in ESC outbreaks is fish health. "Any stress, whether it's water quality or overstocking makes fish more susceptible to disease," says Dr. Jimmy Avery, Extension aquaculture leader at Mississippi State.

"Higher stocking densities increase the efficiency of disease transmission from fish to fish," he adds.

Throw in ESC's temperature sensitivity, and you have a disease outbreak waiting to happen in many catfish ponds.

Research from the Southern Regional Aquaculture Center shows fish that survive an ESC outbreak can carry the bacterium in their brain, kidney and liver up to 200 days. While these fish develop immunity to ESC, they are also able to spread the disease to naïve fish within the pond perpetuating the disease cycle.

Improving ESC Management

Many catfish farmers treat ESC by withholding feed when an outbreak occurs. This plan shortchanges fish on two levels.

"When you stop feeding fish, you reduce the nutrients needed for the larger fish to gain weight, and you decrease the available energy that sick fish need to fight disease," points out Gaunt.

Early detection of ESC through surveillance and good disease-management plans dramatically improves the chance of effective treatment. Catfish farmers who find fish exhibiting the head-chasing-tail whirling behavior or fish hanging head up/tail down in the water need to contact a veterinarian or diagnostic lab for an immediate diagnosis and treatment plan.

"Fish suffering from ESC lose their appetite, and we need to initiate treatment quickly," says Gaunt. "We really need a good antibiotic that the catfish will eat well so that they can continue to feed and gain weight during the growing season. We're optimistic about some of the new antibiotics that could be coming to the catfish market soon."

Bill Hemstreet, fish health specialist with the Alabama Fish Farm Center, says that for many years intensive management and medicated feeds were not popular with catfish farmers.

"Today, however, we see producers moving away from withholding feed to sick catfish," observes Hemstreet. "Larger catfish operations are more proactive in management and use of new disease-fighting technology."

Avery agrees, "With the return to slightly higher profit margins, producers are considering additional fish health tools including antibiotics and vaccines to help fight this disease while maintaining profitability."

Concerned that existing antibiotics may not be doing the job because they are not used properly or have palatability problems, specialists say new-generation feed antibiotics pending approval from FDA could make a big difference in ESC control and, if used correctly, significantly lower the $13 million in losses seen each year by the catfish industry.

ESC Facts and Figures

As the catfish industry grows, so does the prevalence of ESC. Following is a brief history of ESC and its impact on the catfish industry:

  • First recognized as a new infectious bacterial disease of pond-raised catfish in 1976.
  • Causative gram-negative bacterium, Edwardsiella ictaluri, described as new species in 1979.
  • Today ESC accounts for as many as 45 percent of all disease case submissions in the Southeast US.
  • Estimated losses due to ESC are in excess of $13 million.
  • Generally considered to be a temperature-dependant disease occurring from spring to fall.


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