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Research Project: Development of Management Strategies to Mitigate Pre-harvest Microbial-derived Off-flavors in Fish Grown in Aquaculture

Location: Natural Products Utilization Research

Title: Effects of relevant ammonium chloride concentrations on biomass and off-flavor compound production by Streptomyces luridiscabiei originating from a recirculating aquaculture system

Author
item Schrader, Kevin

Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Common preharvest off-flavors such as "earthy" and "musty" in fish raised in recirculating aquaculture systems (RAS) are produced by certain bacteria that grow in the RAS. Higher concentrations of ammonia, a waste product from the fish, were found to promote production of the common off-flavor compounds. Maintaining lower ammonia concentrations in the RAS may help reduce concentrations of the common off-flavor compounds and subsequently the severity of the off-flavors.

Technical Abstract: The preharvest off-flavors “earthy” and “musty” can occur in fish raised in recirculating aquaculture systems (RAS) rendering them unpalatable and unmarketable. These off-flavors are due to the accumulation of geosmin and 2-methyisoborneol (MIB) in the fish flesh. Certain bacteria are attributed to be the main producers of geosmin and MIB in RAS, and Streptomyces luridiscabiei was previously isolated from a RAS and determined to produce both off-flavor compounds. Nutritional factors (e.g., ammonia) can impact production of these off-flavor compounds by Streptomyces spp. In this study, we evaluated various concentrations of ammonium chloride to determine the effects on biomass, geosmin, and MIB production by S. luridiscabiei. Cultures of S. luridiscabiei were incubated under different ammonium chloride concentrations for 28 days and evaluated for biomass, geosmin, and MIB production. Similar biomass production by S. luridiscabiei occurred at the different ammonium chloride concentrations throughout most of the study period. Conversely, significantly higher (P < 0.05) concentrations of geosmin and MIB were produced by S. lurisdiscabiei at the highest ammonium chloride concentration (7.5 mg/L) at 28 days. These preliminary results indicate that maintenance of total ammonia nitrogen concentrations below 1 mg/L may help reduce concentrations of geosmin and MIB in the water of RAS.