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United States Department of Agriculture

Agricultural Research Service

Healthy Animals 42

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Issue 43, October 2010
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ARS Scientists Find Solutions to Help Keep Catfish Healthy

A healthy pig rests its snout on the back of another pig.

Research Briefs

First domesticated turkey genome map. ARS scientists are studying how oxytetracycline, an antibiotic that is administered to animals, breaks down in cattle manure.

Three scientists named to ARS Science Hall of Fame. Three outstanding ARS scientists have been named to the ARS Science Hall of Fame for their research on livestock genetics, parasitic diseases of animals, and milk fever disease in dairy cows.

Blocking E. coli bacteria. ARS scientists have discovered key gene and chemical interactions that allow Escherichia coli (E. coli) O157:H7 bacteria to colonize the gut of cattle.

Innovation is the key for Agricultural Research Service (ARS) scientists looking for ways to keep farm-raised catfish and other aquatic animals healthy and productive. Their research accomplishments, which include superior vaccines to fight pathogens and the fine-tuning of oxygen management systems for ponds, help protect and sustain America's aquaculture industry.

There's More than One Way to Hatch an Egg

For example, an ARS scientist in the Mississippi Delta is on a mission to help commercial growers improve farm-raised catfish production.

Fish biologist Les Torrans is constructing an innovative egg incubator he calls the "see-saw" to provide a better mix of dissolved oxygen for vulnerable catfish eggs. Torrans works in the ARS Catfish Genetics Research Unit of the Thad Cochran National Warmwater Aquaculture Center located at the Mississippi State University (MSU) Delta Experiment Station in Stoneville, Miss.

Torrans devised the "see-saw" after learning about how oxygen levels in fish ponds affect feeding and production, information which led to new oxygen-management recommendations for the ponds. Additional research conducted by Torrans and James Steeby, MSU associate professor emeritus, resulted in specific dissolved-oxygen recommendations for catfish hatcheries.

The two researchers collected data on catfish egg and fry metabolism, which showed that most hatch variations were caused by insufficient dissolved oxygen in the water. The problem was compounded by poor water circulation around and through egg masses, according to Steeby and Torrans.

With the see-saw, egg masses are dipped in water and then lifted out before being dipped again. Egg masses remain wet, enabling them to exchange gas across the egg membrane. Because oxygen in air is more plentiful, the see-saw device takes advantage of the water dipping to maintain the developing eggs' moisture while using the air for oxygen delivery.

The see-saw potentially can speed up catfish production. "More than twice as many eggs are hatched in the same space, and half the amount of water is used with this device," Torrans says.

Torrans' goal is to help revive shrinking catfish hatcheries and boost production for states in the Mid-South, where more than 90 percent of the nation's catfish are grown. One solution is getting more dissolved oxygen to fish, he says. When fish get more oxygen, they eat more and grow to market size faster.

Vaccines Help Prevent Disease in Fish

Vaccines developed by ARS scientists are being used to give the farm-raised catfish industry "a shot in the arm" against disease-causing pathogens that threaten fish.

University of Nebraska-Lincoln engineer David Jones and ARS agricultural engineer Tami Brown-Brandl study a heat stress model.
Catfish farmer Bobby Jones (left) and his father Robert A. "Shorty" Jones, of Needmore Fisheries LLC, observe the "see-saw" egg incubator with co-developer fish biologist Les Torrans (center). The two farmers plan to replace their traditional paddle-type incubators (seen on the right, behind Jones) with the new see-saw device before the next spawning season.

Microbiologist Phillip H. Klesius, research leader at the ARS Aquatic Animal Health Research Unit in Auburn, Alabama, is working with colleagues Craig Shoemaker and Julia Pridgeon in Auburn and Joyce J. Evans, who is based at the unit's worksite laboratory in Chestertown, Md. The group is developing vaccines to safeguard farm-raised catfish and other aquatic animal species against such pathogens as Streptococcus iniae and S. agalactiae.

Researchers modify the genetic makeup of pathogens to make them non-virulent, and then develop vaccines that expose fish to low doses of the modified pathogens. "A live, modified vaccine that has similarities to the pathogen is used to create a lifelong immunity in fish," Klesius says.

S. iniae also can occur in wild fish and in food fish. A modified live S. iniae vaccine developed by Pridgeon and Klesius appears to be superior to inactivated or killed vaccines.

To vaccinate a large number of fish, researchers rely on a method that requires immersing fish in water containing the modified pathogen. However, new techniques that allow vaccine delivery through feeding are being developed.

The catfish industry has already taken advantage of the team's successful vaccine against the pathogen Edwardsiella ictaluri that causes enteric septicemia, one of the most significant economic diseases in catfish.

"In the past 10 years, we've been able to produce several vaccines using modified live bacteria that are no longer viable pathogens," Klesius says. "We patented them and then licensed them to private firms."

David Wise, MSU research professor, and retired scientist Kurt Schuster tested the vaccine for enteric septicemia in 1996. They discovered that the survival rate of fish in 10 ponds jumped by more than 12 percent. In addition, they found that producers who used the vaccine could expect an increase—$1,800 per acre—in returns.

This research supports the USDA priorities of ensuring food safety and promoting international food security.

For more information about this aquaculture research, contact Jeff Silverstein, leader of ARS National Program #106, Aquaculture.

About This Newsletter

ARS Animal Health Research Laboratories

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Last Modified: 2/17/2011
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