New Algicide To Help
Fingerling catfish, about 1 year old.
Blue-green algae give catfish farmers the blues.
Certain types of blue-green algae, or cyanobacteria, produce
off-flavor compounds that can give catfish a muddy or earthy taste,
which keeps them from being marketable. Affected fish are held in ponds
for costly weeks until the compounds leave their bodies.
Currently, catfish farmers choose between two chemical
solutions for fighting the algal menace. Copper sulfate is the only
algicide approved by the U.S. Environmental Protection Agency for such
use on a permanent basis. Diuron, an herbicide containing chlorine,
is used with government permission that must be renewed yearly.
These chemicals control the cyanobacteria, but can be toxic to most phytoplankton, including green algae. Green algae do not cause off-flavors, and they play a significant role as a base for aquatic food chains and as oxygenators for pond water.
Microbiologist Kevin Schrader
examines a culture of green
algae (Selenastrum capricornutum)
used in a rapid bioassay to
screen natural compounds for
selective algicidal activity.
Better help may be on the horizon for many catfish farmers
in the form of a natural-based algicide that kills blue-green algae
but is much safer for other pond life.
The new algicide, the subject of a patent application,
uses a product derivative based on the natural compound anthraquinone,
found in ryegrass (Lolium perenne). It was discovered by scientists
at ARS' Natural Products Utilization
Research Unit in Oxford, Mississippi, in collaboration with biochemist
Dhammika Nanayakkara at the University of Mississippi's National Center
for Natural Products Research.
According to ARS microbiologist Kevin Schrader, the project's
lead scientist, the algicide is ready for additional testing in catfish-filled
ponds. It has shown great potential against its target in laboratory
tests using microplates and in large fiberglass enclosures known as
limnocorrals placed in catfish ponds. Also, catfish exposed to it in
aquarium tests stayed healthy, Schrader says.
ARS is seeking a commercial partner to fully develop and
commercialize the technology.
The algicide targets Oscillatoria perornata, a
species of cyanobacteria prevalent in Mississippi. (That state is home
to half of the nation's catfish farms.) O. perornata produces
the musty compound 2-methylisoborneol, which in turn gives catfish the
muddy type of off-flavor.
Pond testing against O. perornata will continue
to take place in four quarter-acre ponds in Stoneville, Mississippi,
at the Thad Cochran National Warmwater Aquaculture Center, in collaboration
with fisheries biologist Craig Tucker of Mississippi State University's
Delta Research and Extension Center.
In laboratory tests, the algicide, which if approved may
be available in 2 to 3 years, was 40 times less lethal to green algae
than diuron. Also, it rapidly dissipated from the pond water after application,
whereas diuron can be detected for days or weeks after application.
Off-flavor problems cause the $2-billion-a-year catfish
farming industry as much as $50 million in losses annually. See the
March 2003 issue of Agricultural Research magazine for studies
on another approach to controlling off-flavors.By Luis
Pons, Agricultural Research Service Information Staff.
This research is part of Aquaculture, an ARS National
Program (#106) described on the World Wide Web at www.nps.ars.usda.gov.
"New Algicide To Help Keep Catfish Tasting Good" was published in the April 2003 issue of Agricultural Research magazine.