MSU Researchers Identify Biological Method to Control Devastating Catfish Disease

STONEVILLE, Mississippi – A native fish species of the Mississippi River and Gulf slop drainages from Alabama to Texas may have a role to play in stemming the spread of a debilitating catfish disease.

David Wise, a research professor in aquatic animal health at the Mississippi State University Delta Research and Extension Center, has received a Southern Sustainable Agriculture Research and Education (SARE) On-Farm Research Grant to study how well the smallmouth buffalo can control proliferative gill disease.

“Proliferative gill disease, also known as Hamburger Disease, is a significant problem in the catfish industry. It’s the third most commonly diagnosed disease in the Delta,” said Wise.  The disease can cause 100 percent mortality in pond-raised catfish and can threaten the economic viability of small operations.  There is currently no effective way to control it, but we can prevent losses in situations where ponds need to be restocked.”

Proliferative gill disease, which produces swelling of the gills and cuts off proper exchange of oxygen and carbon dioxide, is caused by a protozoan parasite found in a small aquatic worm (dero worm) that lives in the pond sediment. The dero worm releases the free-floating parasitic spore, which infects the gills of catfish. The result is a tremendous inflammatory response whose severity depends on the level of spores in the water and size of the fish.  The life cycle repeats when terminal spores, which develop in the gills, rupture and are released in the water. Those spores infect more dero worms.   As the life cycle continues parasite levels are amplified in a closed system such as a pond. 

“Older catfish tend to be more tolerant of proliferative gill disease. It’s the younger fish that are introduced to the pond during stocking that are highly susceptible to it.  However, high mortality rates can be observed in older food-sized fish when spore levels reach a critical level.  It is this situation where the disease can kill 100 percent of the fish in the pond.” said Wise.  “Because of the cyclical nature of the disease, there are always certain levels of spore counts in the pond, and because the ponds are never drained, catfish are constantly being exposed to the disease.”

One objective of the Southern SARE project is to break the disease cycle by trying to eliminate one of the hosts the parasite depends on for survival.

“Since we can’t get rid of the catfish, then the obvious choice is to get rid of the dero worm,” said Wise.

Nearly a decade of research at Mississippi State University has found that the smallmouth buffalo, a sediment feeder, is an ideal biological control for managing the dero worm. Wise and his colleagues are in their second year of trials at the Delta Research and Extension Center, introducing the smallmouth buffalo to catfish ponds and evaluating their effectiveness in reducing populations of the dero worm.

Matt Griffin, a co-investigator on the project, has developed a molecular test for measuring the number of parasitic spores in pond water. 

“The test provides us with an accurate method of evaluating pond environments to assess the risk of losing fish to proliferative gill disease and evaluating potential disease treatments,” said Griffin. 

“We will use this test to measure the number of spores in the water between ponds stocked with smallmouth buffalo and those with no smallmouth buffalo,” said Wise. “So far we’ve found a statistical reduction in the number of spores in ponds stocked with smallmouth buffalo compared to those without the fish species present. That’s telling us that the smallmouth buffalo is feeding on the dero worm.”

This year, Wise and his colleagues are applying their pond trials to commercial catfish ponds. With the results, along with the spore-count thresholds that have been developed, researchers are hoping to educate fish farmers on the best times to restock their ponds that would result in fewer disease outbreaks, in addition to smallmouth buffalo management strategies.

“We are shooting for a 100-150-acre smallmouth buffalo stocking goal to produce the best disease-management results,” said Wise.

Since blue catfish are highly resistant to proliferative gill disease, another objective of the grant project is to evaluate the effectiveness of hybrid catfish production (a cross between channel and blue catfish) in breaking the lifecycle of the parasite.  While hybrid catfish are susceptible to the disease, preliminary research indicates that parasite does not effectively develop in hybrid catfish. 

“So we are approaching this problem from two sides: lowering parasite loads in the pond by reducing the oligochaete host, and using the hybrid catfish as a culture species to hinder life cycle development in the fish,” said Wise. “We are hopeful that we can have a positive impact on the industry and create an effective strategy to manage the disease. When you lose $10,000 worth of fish, restock it, and then lose another $10,000, it’s not a very sustainable business.”

Commercial catfish production is an important agricultural commodity in the United States. In 2011, catfish growers had sales of $423 million, according to the U.S. Department of Agriculture. The top four catfish-producing states (Mississippi, Alabama, Arkansas, and Texas) accounted for 95 percent of the total sales.

The Southern SARE project, “Biological Control of Proliferative Gill Disease in Farm-Raised Catfish (OS12-068),” is supported by a two-year $14,997 grant.

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Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America's Southern region.