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Title: Evaluation of off-flavor in pond-raised channel catfish following partial crop harvest

item Schrader, Kevin
item TUCKER, CRAIG - Mississippi State University

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2012
Publication Date: 6/29/2012
Citation: Schrader, K., Tucker, C.S. 2012. Evaluation of off-flavor in pond-raised channel catfish following partial crop harvest. North American Journal of Aquaculture. p. 385-394.

Interpretive Summary: Farmers of pond-raised channel catfish raised in Mississippi have reported that catfish remaining in a pond following partial crop harvest will develop off-flavors, thereby rendering them unpalatable and unmarketable. The study concluded that there were no changes in fish flavor quality after partial harvest of a crop of catfish. In addition, there were not any changes in ecological conditions that caused off-flavors to appear in catfish after partial crop harvest. Inadequate sampling from mixed-flavor populations of catfish prior to harvest are likely the reason for the farmers’ observations.

Technical Abstract: Channel catfish Ictalurus punctatus ponds 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 if fish systematically develop off-flavors after partial fish harvest and, if so, the type and origin of the flavor. Catfish and water samples were obtained from 12 ponds prior to initial harvest and then at intervals for 2 weeks after harvest. Water and catfish fillet samples were analyzed for geosmin and 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. In four ponds, waterborne MIB concentrations increased the day after initial harvest; however, MIB concentrations in two of those ponds eventually decreased or returned to levels that were similar to those prior to harvest. One-way analysis of variance 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 causing an increase in odor-producing cyanobacteria.