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TacklingTaint Could Boost Market Postion

MISSISSIPPI - The US Catfish market is static and flavour problems are hampering progress in what is becoming an increasingly competitive international market, says advisers at Mississippi's State University.

US producers are battling to consistently deliver delicious fillets to consumers, they are losing out to imports and valuable market potential.

Farmers need to focus on delivering a high-quality product that is reared as efficiently as possible, saidTerry Hanson, an agricultural economist with the Mississippi State University Extension Service. Poor flavour is a very serious problem for the farmed catfish industry and producers must adopt control strategies to minimise the chances of producing tainted meat.

“Survey information indicates that every pond in the Mississippi catfish industry averaged seven 'off-flavour' occurrences a year. The off-flavour prevents ponds from being harvested an average of 59 days per pond each year,” he explained.

Studies by the Mississippi Agricultural and Forestry Experiment Station, show that these flavour-related harvest delays cost Mississippi's industry an average of $23 million a year between 1997 to 1999. The situation has improved since then, but the flavour issue remains a key problem in developing the market and improving returns.

Flavour problems are reducing market potential for US Catfish.

Taint is often caused by odorous compounds in the water or feed of catfish. These are absorbed across the gills or the gastrointestinal tracts of catfish and deposited in fatty tissues. The compounds are eventually are metabolized or excreted, but the meat will be 'off-flavour' if the fish are harvested while the compounds remain in their bodies. .

Scavenge effects

Craig Tucker, a MAFES researcher at the Thad Cochran National Warmwater Aquaculture Center in Stoneville, described the off-flavours include 'fishy,' 'rotten fish' or 'decay/vegetal'. These can be caused when fish scavenge for foods other than the manufactured diets provided by the farmer. With good feed management, these off-flavours are not very prevalent, but it can take months for fish to purge these from their systems.

Other common water-borne off-flavors are described as 'musty' or 'earthy', are mostly found in the summer and are algae-related. But this can be treated effectively.

“Musty off-flavour is the most common natural phenomenon. It’s very difficult to change what nature wants. Nature wants blue-green algae in ponds, and it’s very hard to manage them out,” said Mr Tucker Jim Steeby, aquaculture specialist with the Mississippi State University Extension Service, said off-flavour most commonly occurs in the warm-weather months and so treatment regimes should be strategically targeted to counteract potential problems.

“Our treatment season starts in mid-April to May until water temperatures drop below 70 degrees, usually in late October,” Steeby said. He is encouraging growers to work on their off-flavour problems going into the fall because once the water temperatures get below 70 degrees, off-flavour compounds tend to subside, although they can still remain in catfish tissues due to the fish's lower metabolic rate.

Off-flavour problems caused by algae can be corrected quickly during the summer months, when water temperatures are warm, but they can take months to remedy in colder climates.

“If you have fish that are off-flavour, there is no instant way to fix it,” You must solve the algae problem and allow the fish to purge,” advised Mr Tucker.

Algal problem

Two types of blue-green algae are responsible for the problem and both are easy to identify:

  • MIB, produced by Oscillatoria perornata,
  • Geosmin, produced by a species of Anabaena
“If the fish have an earthy, musty flavour, the water should be checked under a microscope for odorous algae. If you have it, you can treat it. If they’re not there, you have to just wait," Tucker said And it is vital to ensure the presence of the algae before treating the pond because pools can be clear of algae faster than the catfish can purge the compounds from their systems.

“The off-flavour in the fish may be from algae present a few weeks before you checked the pond. If odour-producing algae are not present, using herbicides will not help,” he added.

Alternatives

Copper sulphate is the most common treatment for blue-green algae, but this chemical can be difficult to dissolve and often sinks to the bottom of the pond.
Using Diuron will become and option this year. The chemical is about to receive full registration for use in catfish ponds after 10 years evaluation through the licensing process.

“Diuron takes a long time to work, but is much less expensive than the alternatives,” said Tucker.

Ellen Hardy

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