Location: Natural Products Utilization Research2011 Annual Report
1a. Objectives (from AD-416)
1)Discover and develop management strategies for mitigating pre-harvest microbial-derived off-flavors in fish cultured in re-circulating aquaculture systems (RAS) to help reduce off-flavor delayed harvest. 2)Discover and conduct primary development of novel natural and natural-based compounds for controlling disease causing microorganisms in pond-based production systems.
1b. Approach (from AD-416)
Isolate and identify the microorganisms responsible for the most common environmental off-flavors in finfish cultured in recirculating aquaculture systems (RAS). Perform laboratory physiology studies on the off-flavor microorganisms to determine the environmental and nutritional conditions that favor growth and production of the off-flavor compounds. Conduct depuration studies to identify factors such as adipose content of the fish flesh and fish size that may affect depuration rates. Perform efficacy studies to determine if activated carbon filtration can be utilized to reduce levels of the off-flavor compounds in the RAS water and subsequently in fish flesh. Determine the efficacy of antifouling coatings to reduce biofilm formation on RAS culture tank walls and subsequently reduce levels of microbial off-flavor compounds in RAS-cultured fish. Conduct bacterial bioassays to identify natural or natural-product based compounds as potential leads for use in managing diseases in catfish aquaculture. Perform primary development of promising natural compounds identified from bacterial bioassays for use as therapeutic drugs to manage common catfish diseases and improve catfish health.
3. Progress Report
In 2010-2011, several species of odorous bacteria were isolated from organic matter obtained at different locations within a series of recirculating aquaculture systems (RAS) at the research facility located at the National Cold Water Marine Aquaculture Center, Franklin, Maine. These novel isolates of odor-producing bacteria were determined to be contributors to the earthy-musty off-flavor in the RAS-cultured Atlantic salmon. The identification of the microbial sources of earthy-musty taints in RAS-cultured fish is the first step in the development of methods to mitigate the earthy-musty off-flavor problems that may occur in RAS-cultured finfish. Purging studies of off-flavored Atlantic salmon were completed in collaboration with The Conservation Fund Freshwater Institute, Shepherdstown, West Virginia, and with the National Cold Water Marine Aquaculture Center, Franklin, Maine, in order to determine the holding time to adequately reduce levels of an earthy compound in the flesh of Atlantic salmon and subsequently provide “on flavor” and good-tasting product for consumers. Sensory analysis of the Atlantic salmon samples collected during the purging studies confirmed that high-quality, good-tasting Atlantic salmon were obtained after the depuration period. A crude extract obtained from a plant was determined to possess strong antibacterial activity towards a bacterial species that causes a common disease in pond-raised channel catfish. Bioassay-guided fractionation of the crude extract is continuing in order to determine the active compound(s). A plant compound that was previously discovered to possess antibacterial activity towards a disease-causing bacteria species of pond-cultured channel catfish was used as a template to produce analog compounds for structure-activity relationship studies in order to identify another form of the compound with stronger antibacterial activity.
1. Identification of the cause of earthy-musty off-flavors in recirculating aquaculture system (RAS)-cultured fish. Preharvest off-flavors described as “earthy-musty” in fish produced in recirculating aquaculture systems hamper the growth of this industry. An ARS researcher at University, Mississippi, determined the compounds and microorganisms responsible for earthy-musty off-flavors in fish including arctic charr, barramundi, rainbow trout, and Atlantic salmon cultured in recirculating aquaculture systems. The discovery of the responsible compounds and determining their concentrations in fish flesh have allowed the development of purging management practices that will reduce the levels of the off-flavor compounds in the fish flesh in order to provide a good-tasting, high-quality product to consumers. These management practices have reduced off-flavor delayed harvests and subsequently reduced the economic losses of producers that occur during delayed harvest such as additional feeding costs and losses of fish to disease and water quality problems.
Schrader, K., Andolfi, A., Cantrell, C.L., Cimmino, A., Duke, S.O., Osbrink, W.L., Wedge, D.E., Evidente, A. 2010. A survey of phytotoxic microbial and plant metabolites as potential natural products for pest management. Chemistry and Biodiversity. 7:2261-2280.