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Work to Rid Catfish of Off-flavors
By Jim Core
March 7, 2003
Catfish producers can minimize the
chance of off-flavors in their fish by raising them in newer ponds with fresher
water that's less likely to contain algae and bacteria that cause the
off-flavors, according to Agricultural
Research Service scientists and cooperators.
Algae and bacteria, which thrive in the nutrient-rich ponds, produce
compounds that cause fish that eat them to taste woody, rotten, like sewage, or
similar to diesel fuel.
Paul Zimba, a microbiologist at ARS'
Genetics Research Unit in Stoneville, Miss., studies the biology of
blue-green algae, called cyanobacteria, and other species that are the sources
of geosmin, 2-MIB, and other off-flavor compounds. The catfish industry's most
common management system may contribute significantly to the growth of
off-flavors, according to Zimba.
In the multiple-batch system, hatched fish eggs, or sac fry, are reared in
nursery ponds. Once they reach the fingerling stage, they're moved up to ponds
where they grow to market size. The restocking process can continue for several
years with several different ages of catfish present at any one time and
without the ponds being drained.
The researchers found that water in older ponds contained higher densities
of off-flavor-causing zooplankton than water in newer ponds. Older ponds may be
best suited for holding sac fry and fingerlings, according to Zimba. The larger
zooplankton in these ponds could serve as fry food, while younger ponds would
be better suited for growing out fish and purging potential off-flavors.
Zimba and Steven J. Thomson, an agricultural engineer in Stoneville, are
also studying a remote sensing technique that may detect unwanted algal species
in production ponds before the problem gets out of hand.
They and their collaborators shot digital video during low-altitude flights
over ponds to obtain unwanted algae's unique color profiles. They're working to
understand the specific relationships in catfish ponds to predict occurrence of
ARS is the U.S. Department of
Agriculture's chief scientific research agency.
Read more on this research in the
March 2003 issue of
Agricultural Research magazine