“Pond-raised catfish should have a very mild flavor,” said Craig Tucker, director of the Thad Cochran National Warmwater Aquaculture Center in Stoneville. “Off-flavored catfish creates a severe economic hardship for catfish farmers because the fish are not marketable. Off-flavor prevents the timely harvest of fish, raises production costs, interrupts cash flow and disrupts the transfer of fish to processors.”
(Photo by MSU Delta Research and Extension Center/Rebekah Ray)
MSU researchers have developed a chart describing the many individual flavors detected in pond-raised catfish. Acceptable or positive flavors include chickeny, buttery, nutty and sweet corn. Negative flavors include fishy, stale, metallic, woody, earthy, musty and moldy.
In checking for flavor, researchers collect catfish from a pond and immediately fillet them. In the lab, the samples are washed in clean water, and the unseasoned fillets are briefly microwaved. Trained taste-testers then assess the aroma and flavor of the unseasoned samples, which are then ranked on a numerical scale.
“If the sample is off-flavor, harvesting in that pond is delayed until the problem can be corrected and the flavor improved,” Tucker said.
For the past 18 years, research associate Margaret Dennis has helped set up taste tests at the aquaculture center. She said becoming a taste-tester requires time and training.
“When I began, I could not tell much difference in the subtle flavors of catfish, but after going through the training process, I learned how to do it,” Dennis said.
Off-flavor problems can originate from several sources, including diet, pollution and the environment. While catfish off-flavors from diet are possible, it is rare in pond-raised fish, which are usually fed high-protein commercial feed of soybeans, corn, wheat, vitamins and minerals. During the winter months, however, farmers may not routinely feed their fish, and fish forage on natural foods and develop undesirable flavors.
“Sometimes even in the controlled environment of catfish ponds, we find off-flavors that result from fish eating foods such as detritus and other organic materials located on the bottom of ponds,” Tucker said.
Most flavor problems are caused by odorous compounds produced by microorganisms naturally occurring in the water. Algae or bacteria are released into water and absorbed through fish gills or skin, or into the intestinal tract. The compounds are deposited in fatty tissues and produce undesirable off-flavors. Although these compounds are harmless, they have an intense odor.
“The most common off-flavors have been described as earthy, muddy, moldy or musty, and these result from blue-green algae. The only way to know what algae are present in a pond is to examine the pond water under a microscope,” Tucker said.
Musty or muddy off-flavors develop rapidly and disappear more slowly. Once the flavor develops, the key is to eliminate the algae causing the problem and let the fish naturally purge the chemical.
“After treating the pond with an algaecide, fish should be sampled daily for flavor quality because the musty or muddy off-flavors usually disappear from fish within a few days in warm water,” Tucker said.
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