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Abstract
Ponds used to raise channel catfish Ictalurus punctatus in the southeastern United States often contain more food-sized catfish than processors can accept at one time. Fish remaining after initial harvest are returned to the pond and harvested again as soon as possible based upon processor demands. Some catfish farmers report that catfish crops initially declared “on-flavor” appear to develop off-flavors soon after the first harvest, which postpones harvest of the remaining population and delays subsequent production. We conducted a 9-month study on a commercial catfish farm in northwest Mississippi to determine whether fish systematically develop off-flavors after partial fish harvest and, if so, the type and origin of the flavor. Channel catfish and water samples were obtained from 12 ponds before initial harvest and then at intervals for 2 weeks after harvest. Water and catfish fillet samples were analyzed for geosmin and 2-methylisoborneol (MIB). Phytoplankton were identified and counted microscopically. Catfish fillets were also used in sensory analysis to determine quality and intensity of off-flavor. In most ponds, MIB levels decreased or remained unchanged in pond water after the first seining while geosmin levels remained very low (<10 ng/L) in all ponds. Analysis indicated that mean MIB concentrations in catfish fillets either decreased or were unchanged after the initial harvest. Similar results were found for geosmin concentrations in catfish fillets. There was also no systematic change in fillet flavor quality as determined by sensory analysis. The MIB-producing cyanobacterium Planktothrix perornata was found in only three ponds, and the abundance of P. perornata decreased in two ponds after initial harvest and transiently increased in the third pond. Overall, we found no systematic changes in fish flavor quality after partial fish harvest and no indication that harvest activities changed ecological conditions that would cause an increase in odor-producing cyanobacteria.
Received November 10, 2011; accepted February 14, 2012
ACKNOWLEDGMENTS
The technical assistance of Margaret Dennis, Dewayne Harries, Sue Kingsbury, and Phaedra Page is greatly appreciated.