Submitted to: Proceedings of the International Conference on Recirculating Aquaculture
Publication Type: Proceedings
Publication Acceptance Date: 4/10/2012
Publication Date: 8/24/2012
Citation: Schrader, K. 2012. Preliminary studies on the depuration of common off-flavors from fish raised in recirculating aquaculture systems. In: Proceedings of the 9th International Conference on Recirculating Aquaculture. p. 20-21.
Technical Abstract: “Off-flavor” problems can adversely impact the growth of the aquaculture industry. Fish raised in recirculating systems have the potential to develop the common off-flavors “earthy” and “musty” due to accumulation of the microbial metabolites geosmin and 2-methylisoborneol (MIB) in the fish flesh. These compounds can be rapidly taken up by fish from the water by passive diffusion across the gills and by absorption across the epithelial lining of the gastrointestinal tract from water swallowed concurrently while feeding. While uptake and bioaccumulation of geosmin and MIB in fish flesh can occur within minutes, the elimination of these lipophilic compounds can take days or weeks and may depend on several factors including the intensity of the bioaccumulated compounds in the flesh, water temperature, and adipose content of the fish flesh. One common management approach used by aquaculturists in mitigating geosmin and MIB-related off-flavors is depuration of the preharvest off-flavors. Currently, the best management approach available to commercial aquaculturists utilizing recirculating aquaculture systems (RAS) is purging earthy and musty off-flavors by moving the aquatic animals to an aquatic system that is free of the odorous compounds. However, little or no studies have been conducted on certain freshwater fish species raised in RAS to determine the length of time required to purge geosmin and MIB to obtain “on-flavor” fish. In this presentation, the results of several recent purging studies on Atlantic salmon (Salmo salar), coho salmon (Oncorhynchus kisutch), and rainbow trout (Oncorhynchus mykiss) produced in RAS will be discussed. These studies were performed using fish samples obtained from several different locations including research and commercial facilities. Fish were sampled from purging systems over a period of days, and fillet samples were analyzed for concentrations of geosmin and MIB using microwave distillation and solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). In addition, sensory analysis was performed on fillets to determine flavor quality and acceptability of fish at the end of the purging period. Concentrations of geosmin and MIB in the water used to purge the fish were determined by SPME-GC-MS in order to verify suitability of the purging water. Overall, results revealed that reduction of geosmin and MIB in the fish flesh to minimum concentrations could be achieved in 10 days or less, thereby providing an acceptable tasting and marketable product.