Catfish Disease Report Shows Heavy Losses


Specialists Urge Farmers to be More Proactive with Diagnostics

Catfish farmers should strive to be more proactive managing disease, not just to stop death losses, but to optimize fish performance and profitability.

The most recent data from the USDA's National Animal Health Monitoring System (NAHMS)—which makes periodic surveys and assessments of animal health management practices on commercial livestock farms across the United States—shows dramatic differences in the number of pond fish harvested compared with the number of pond fish stocked.

In fact, mortality rates can be as high as 60 percent in pond fish and more than 30 percent from fry to fingerlings. Specialists say that such a huge mortality rate is unnecessary and totally unacceptable. More than 50 percent of these losses are from enteric septicemia of catfish (ESC) associated with Edwardsiella ictaluri and columnaris associated with Flavobacterium columnare.

More bad news: While these numbers are shocking, Dr. Patricia Gaunt, Associate Professor, Aquatic Animal Health, Mississippi State University College of Veterinary Medicine, estimates that death losses may be underreported due to the voluntary nature of the NAHMS surveys. In other words, the situation could be much worse than what NAHMS reported.

Gaunt says good disease control is profitable in any market, but it's especially important now with prices up 8.5 percent over last year.

Why so high?

Part of the problem is the way catfish are produced. "Catfish farmers often don't know the inventory of the pond because they're periodically stocking and harvesting fish," she points out.

The best way to get more catfish out of the pond is to keep them healthy and growing. Constant surveillance of catfish ponds is one way to catch problems earlier and provide more management opportunities.

Being more proactive with diagnostics—that is, working closely with a veterinarian or diagnostic lab to anticipate and stay ahead of common problems like ESC—can also lead to better disease control, lower mortality and improved performance. Early diagnostics will also allow farmers to make better use of new-generation antibiotics, the first of which is expected to be approved later this year.

"Catching a disease flare-up early allows us to start treatment while the fish are still eating, which is critical," says Gaunt. "This helps ensure they receive a therapeutic dose before they lose their appetite."

The majority of catfish farmers today practice "understocking," where they continuously add small fish to the pond as the largest fish are harvested. This practice sets up a continuous disease cycle in the pond.

"Understocking creates an 'accident-waiting-to-happen' scenario," stresses Gaunt. "You're exposing small fish to every disease in the pond all at once."

Jimmy Avery, Extension Aquaculture leader at Mississippi State University , agrees.

"Newly stocked fish often become infected and need to be targeted for treatment, but larger, resident fish eat the medicated feed targeted for the smaller ones who need it," he points out. Larger pond fish have often experienced repeated disease exposure and have developed a level of immunity to ESC.

All-in/all-out

A growing number of catfish farmers are moving to all-in/all-out management of fish ponds. A similar system has been used for many years in the pork industry and has many advantages when compared to a multi-batch system. The prime advantage to this system is the potential to create a healthier pond environment. Disease transmission from older, carrier fish is minimized because a single size-class of fish is stocked. Also, treatment regimes are simplified since only one size-class of fish would need to be targeted.

While it is estimated that less than 15 percent of the catfish industry has adopted this management plan, it is gaining converts, Avery says.

"All-in/all-out gets catfish to market faster because there's less competition between size groups in the pond," he explains. "Fish are no different than other livestock. Managing the stressors that can trigger disease is an important management tool."

Another way to help catfish survive and thrive is through acclimatization.

Bill Hemstreet, fish health specialist with the Alabama Fish Farm Center, explains that raceway systems improve fish health and nutrition.

"Farmers slowly add pond water to the raceways, gradually exposing the fry to diseases found in the pond," says Hemstreet. "This makes it easy to detect and treat disease before mortality reaches the 30-40 percent level found in pond-raised fry."

The raceway system protects the fry by keeping them in troughs where they can be closely monitored and fed intensively for 2-4 weeks. "Everyone is much more sensitive about mortality with increased prices," says Hemstreet, "and farmers are more likely to treat fish with antibiotics because it's in their interest to keep them alive."

Follow the rules

It's important to follow the recommendations on the antibiotic's label, however. Gaunt says taking shortcuts - not using the full dose of antibiotic or not feeding it for the prescribed treatment period - will reduce their effectiveness and make it easier for resistance strains to develop.

Triggered by today's higher prices for food fish and the increased value of fingerlings, farmers are looking for ways to improve fish weight and production.

According to Hemstreet, another consequence of recent high feed costs is that small fingerlings that can't be harvested by the end of the year. "The bottom line is they just didn't feed the fingerlings like they should have and now there's a real short market for good-sized fingerlings," he adds.

Many farmers also stop feeding catfish during cold weather, believing that pond plankton will fulfill their nutrient requirements. Not so, argues Gaunt.

"Farmers should decrease feeding levels but stopping feed shorts fingerlings on energy needed to fight disease pathogens and maintain growth," she explains.

"When you stop feeding fish for any reason—weather, disease, cost containment—you stop supplying nutrients and energy," stresses Gaunt "and without nutrients and energy, they can't grow. And if they can't grow, they can't reach market weight and size. It's that simple."

Rethink your approach

While these fish experts agree that there is no definitive model for making treatment decisions, ignoring the disease threat won't make it go away.

According to Gaunt, improved profit levels are helping catfish farmers rethink their approaches to disease management and increase their interest in taking management programs to a new level. However, current production systems complicate treatment options.

Closely monitoring the pond environment and fish health gives farmers a head start on treatment options, whether it's improving aeration or feeding an antibiotic.

"Survival rates improve dramatically when treatment is initiated quickly," stresses Gaunt.

"We need to use every tool we can get, whether it's medicated feed, vaccine, environmental controls or management systems," acknowledges Hemstreet, "because there is not a lot in the toolbox right now."

Adds Gaunt, "New-generation antibiotics will also require good management, otherwise the producers won't realize the full benefit of these products."

The Cost of Disease

According to NAHMS data, ESC ( E. ictaluri) and columnaris
( Flavobacterium columnare) top the list of infectious catfish diseases. Records from the Mississippi State University Fish Diagnostic Laboratory in Stoneville show that columnaris accounted for 40.9 percent and ESC 30.7 percent of total disease cases reported in 2004.

The cost of individual diseases is often difficult to put a dollar figure on because they're based on farmer estimates reported to NAHMS.

"We suspect that these loss figures are underreported," says Dr. Patricia Gaunt, associate professor, aquatic animal health, Mississippi State University College of Veterinary Medicine.

For fry and fingerling, mortality levels range from 30 to 50 percent or more. According to Gaunt, this translates into losses of more than 20 million fingerlings in Mississippi alone. Tally it up and fingerling losses top $1.25 million per year.

Estimates of catfish industry dollar loss

ESC
28 percent
$13.5 million
Columnaris
23 percent
$10.8 million
Winter kill
10.1 percent
$ 4.8 million
Visceral toxicosis
3.8 percent
$1.8 million
Proliferative gill disease
2.7 percent
$1.3 million
Anemia
2.2 percent
$1.0 million

 [ Mississippi State University ]

 


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