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Algicide Offers New Way to Fight Off-Flavor in Catfish

Catfish farmers made sad and blue by blue-green algae that cause off-flavors in their fish may soon get some relief. Agricultural Research Service scientists have discovered a natural-based algicide that not only kills the algae in fish ponds, but is notably safer for other pond life when compared to current treatments.

The algicide, which is the subject of a patent application, uses a product derived from a compound found in ryegrass. It was discovered by researchers led by microbiologist Kevin Schrader at ARS' Natural Products Utilization Research Unit in Oxford, Miss. The work was done in collaboration with biochemist Dhammika Nanayakkara at the University of Mississippi's National Center for Natural Products Research, also in Oxford.

The research targets a species of blue-green algae prevalent in Mississippi, home to half of the nation's catfish farms. This algal species produces a musty compound that can be absorbed by the catfish, giving them a "muddy" type of off-flavor.

Currently, catfish farmers choose between two chemical treatments for the $50-million-per-year problem: copper sulfate, the only U.S. Environmental Protection Agency-approved algicide for such use on a permanent basis; and diuron, a chlorine-based herbicide that can be used only with government permission on an annual basis. Both of these treatments can be toxic to most phytoplankton, including green algae that do not cause off-flavor.

In laboratory tests, the algicide was 40 times less lethal to green algae than diuron. It also rapidly dissipated from pond water within hours, whereas diuron can be detected for weeks after application.

After showing great potential in the laboratory and in fiberglass enclosures placed in ponds, the algicide will now be tested in catfish-filled ponds. If approved as a biopesticide, the new algicide may be available in two to three years. ARS is seeking a commercial partner to fully develop and commercialize the algicide.

More information can be found in the April 2003 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.