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Title:   Author  item
                                            Schrader, Kevinitem
                                            DAVIDSON, JOHN - Freshwater Instituteitem
                                            SUMMERFELT, STEVEN - Freshwater Institute
  Submitted to: Aquacultural Engineering
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 9/23/2013
                                    Publication  Date: 12/1/2013
                                    Citation: Schrader, K., Davidson, J.W., Summerfelt, S.T. 2013. Evaluation of the impact of nitrate-nitrogen levels in recirculating aquaculture systems on concentrations of the off-flavor compounds geosmin and 2-methylisoborneol in water and rainbow trout (Oncorhynchus mykiss). Aquacultural Engineering. 57:126-130.Interpretive Summary: The most common types of preharvest off-flavor problems in fish raised in recirculating aquaculture systems are caused by the accumulation of microbial-produced “earthy” and “musty” compounds.  The effects of low and high nitrate levels in recirculating aquaculture systems on concentrations of the earthy and musty off-flavor compounds in the water and rainbow trout were monitored.  The different concentrations of nitrate that can occur in recirculating aquaculture systems did not promote or inhibit the concentrations of the earthy compound in the water or trout.
                                Technical Abstract: Aquatic animals raised in recirculating aquaculture systems (RAS) can develop preharvest “off-flavors” such as “earthy” or “musty” which are caused by the bioaccumulation of the odorous compounds geosmin or 2-methylisoborneol (MIB), respectively, in their flesh.  Tainted aquatic products cause large economic losses to producers due to the inability to market them.  Certain species of actinomycetes, a group of filamentous bacteria, have been attributed as the main sources of geosmin and MIB in RAS.  Previous studies have demonstrated that certain nutritional factors can stimulate or inhibit bacterial biomass and geosmin production by certain actinomycetes.  In the current study, the effects of two nitrate-nitrogen (NO3--N) levels (20-40 mg/L and 80-100 mg/L) on geosmin and MIB levels in culture water and the flesh of rainbow trout (Oncorhynchus mykiss) raised in RAS were monitored.  Water and fish tissue samples were collected over an approximately nine-week period from six RAS, three replicates each of low and high NO3--N, and analyzed for geosmin concentrations using solid phase microextraction-gas chromatography-mass spectrometry.  Results indicated no significant difference in geosmin concentrations in water or fish flesh between the low and high NO3--N RAS.  Therefore, higher NO3--N levels that may occur in RAS will not adversely or beneficially impact geosmin-related off-flavor problems.


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