MSU scientists at the Thad Cochran Warm-water Aquaculture Center have developed a vaccine to protect catfish from commonly occurring bacteria that can cause death. During their first growing season, every catfish fingerling raised in the Mississippi Delta will be exposed to Edwardsiella ictaluri, the bacteria that cause enteric septicemia, or ESC.

In 2013, catfish farms covered 48,600 surface acres of ponds across Mississippi. The production across 125 operations totaled $178 million. ESC is estimated to reduce production by 25-30 percent, costing the industry $30-40 million annually.

“This vaccine has the potential to fundamentally improve the economic viability of the catfish industry because of its positive effects on survival, growth and feed conversion,” said Wes Burger, associate director of the Mississippi Agricultural and Forestry Experiment Station. “Scientists in the Experiment Station are focused on developing a commercialization strategy that will enable catfish producers to operate more efficiently with increased profitability.”

ESC outbreaks typically occur in late summer or early fall as water temperatures cool. Some ESC cases are mild while others cause death. The chronic infection occurs in, and subsequently kills, five to 20 percent of the surviving population that goes through an outbreak.

In 2008, David Wise, MAFES aquaculture scientist developed a live-attenuated vaccine and method of delivering the vaccine orally with commercially available feed. Over the next few years, the vaccine was shown safe and effective in laboratory tests, small pond trials and commercial-scale field trials.

Protocols for vaccine production and processing were developed and validated in field trials. By 2012, the team was using a catfish vaccine delivery system developed by MAFES agricultural and biological engineers in field trials. A utility patent on the vaccine and delivery method is currently pending.

The only time researchers can manipulate the catfish is when they leave the hatchery as fry or leave the nursery pond as adult catfish.

Previously, fry had been vaccinated through immersion baths at seven to 10 days old. The fry were too young with underdeveloped immune systems so the vaccine was only partially effective. The immersion baths as the fish left the hatchery weren’t effective, and fish coming out of the nursery ponds were already exposed to the bacteria.

The new vaccine and method allowed researchers to vaccinate a fully developed fish in the nursery pond.

The team started off mixing the vaccine and feed in a little bucket. They ran a study and it worked.

“A lot of things you do in disease research don’t work,” Wise said. “I haven’t seen anything like this.”

The team proved the concept in five-gallon buckets, but needed a better delivery system.

“You can’t vaccinate a 10-acre pond with a five-gallon bucket,” Wise said. “We had to come up with a method of mixing and administering the vaccine in 500, 800 or 1,000 pounds of feed at a time.”

The challenge lay in the vaccine itself. It has to be live to work. Once the vaccine is absorbed into the feed, it has 20 minutes before it starts losing viability.

The team used a modified seed coater on 1-acre ponds. They were able to mix up 150 pounds of feed but needed something on a commercial scale.
Wise reached out to MSU’s agricultural and biological engineering department, which finished the prototype for the first delivery system in six months, just in time to start vaccinating the fish.

The first delivery system holds up to 1,000 pounds of feed and can administer feed to two 8-acre ponds before reloading. The team recently finished work on a larger delivery system that holds 2,000 pounds of feed and can feed up to four 8-acre ponds before reloading.
Survival and size of the catfish both increased as a result of the vaccine.

“In an aquaculture study, if you have a treatment effect that really improves survival, typically your fish get smaller. Economic returns are based on a balance between size and density,” Wise said. “You could have 100 percent survival in smaller catfish and actually make less money because there is a sliding scale on how catfish are priced. A small catfish is worth less than a larger catfish. In this study, which is very unusual, we had twice as many catfish and they were 20 percent larger.”

The feed conversion ratio was also reduced from approximately 2.5 to 1.5, meaning that it takes a full pound less feed to produce a pound of fish. The team has seen similar results in repeated pond trials that have resulted in two-to-three fold increases in projected gross sales.

Collaborators include USDA’s National Biological Control Laboratory, the MSU Agricultural and Biological Engineering Department in conjunction with the USDA ARS Poultry Research Unit, MSU College of Veterinary Medicine, Thad Cochran Warm-water Aquaculture Center, and the Mississippi Agricultural and Forestry Experiment Station.

Data required to support a USDA licensing application that would make the vaccine commercially available is currently being collected in field trials.

To learn more about MSU's catfish vaccine check out page 18 in the new magazine MAFES DISCOVERS, click here.

By Vanessa Beeson