MISSISSIPPI STATE -- Catfish that don't taste right when headed for the processing plant won't make it to the dinner table until they do, a setback that costs the industry millions of dollars a year.

Mississippi processed about 315 million pounds of catfish in 1997, making catfish one of the top four agribusinesses in the state. An important reason for the success of the industry is the consistently mild, sweet flavor of the fish grown in ponds.

Substances causing the off-flavors in catfish are not toxic, but make the fish unmarketable. These flavors do go away with time, but increase the cost of production while the fish are being held over.

Dr. Craig Tucker, Mississippi Agricultural and Forestry Experiment Station fisheries biologist, works with catfish pond water quality management. He said off-flavored catfish increase the cost of production 5 to 20 percent and is a major marketing problem.

"A very conservative estimate of the cost of off-flavor for Mississippi farmers is estimated to be $16 million a year," Tucker said.

Off-flavor in catfish is any objectionable flavors in the meat. Consumer satisfaction is jeopardized when off-flavored fish make it to market.

"Producers consider off-flavor their biggest production-related problem, and it's been that way since the industry began," Tucker said. "Holding fish in inventory while waiting for the off-flavor to leave fish increases the length of time needed to raise a crop."

This interruption results in lost income from delayed harvest and from forfeit of income from missed sales because the producer cannot restock fish and grow the new crop.

Tucker is one of just a few scientists studying the problem of off-flavor in hopes of finding a way to ensure good-tasting catfish always arrive on the dinner table. Dr. Chris Dionigi is also working on the problem with the U.S. Department of Agriculture-Agricultural Research Service in New Orleans.

"The goal of this research is to be able to harvest a select pond at a predetermined time and know that it is on-flavor," Dionigi said.

Much of the off-flavor in catfish is due to the growth of algae in the ponds. Dionigi said Oscillatoria chalybea is the main culprit for off-flavor. This algae produces two substances that cause an earthy flavor in the fish when absorbed by the gills and prevent the fish from being harvested on schedule.

Harvesting fish on schedule is very difficult. Catfish ponds are tested for flavor twice before harvest, but many shipments still end up being rejected at the processing plant for off-flavor.

"It's possible for both off- and on-flavor fish to be in the same ponds over brief periods," Dionigi said.

Tucker said the problem of off-flavor is ancient, dating as far back as a published account in 1550 of muddy flavor in certain fish. A method used centuries ago of putting the fish in clean water to remove the off-flavor is still the most dependable method used today.

Researchers at MSU and USDA are studying methods of preventing fish from being off-flavor. Possible solutions to this problem are being studied, such as using herbicides to kill the flavor-causing algae and changing ponds' environment so the algae do not occur.