Location: Natural Products Utilization Research2012 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 collaboration with The Conservation Fund Freshwater Institute, Shepherdstown, West Virginia, the effects of high and low levels of nitrate-nitrogen in the water of recirculating aquaculture systems (RAS) were determined to not adversely impact the concentrations of an earthy off-flavor compound in the flesh of rainbow trout raised in the RAS. In another study, rainbow trout possessing earthy off-flavor were held in a flow-through purging system for 7 days that resulted in a significant reduction of concentrations of the earthy off-flavor compound in the fish flesh to provide an acceptable and marketable product. A patented natural-based algicidal compound was incorporated into a slow-release-based coating which then underwent efficacy testing to determine the inhibition of algal and biofilm formation on polyvinyl chloride (PVC), a common material used in certain components of RAS. The high concentration of algicidal test compound demonstrated adequate inhibition of algal growth which can contribute to biofilm on components of RAS; biofilm can contain significant concentrations of common off-flavor compounds as well as harbor fish pathogenic microorganisms in RAS. Biofloc technology systems (BFT) that were used to culture channel catfish were determined to reduce the intensity of earthy and musty off-flavor problems. These BFT were found to be unfavorable for the growth of the common types of blue-green algae responsible for producing earthy and musty compounds that can occur in catfish production ponds. In addition, higher feed applications rates to the BFT were found to correlate with a greater potential for musty off-flavor problems. A novel natural compound from a plant was discovered to possess antibacterial activity against one type of bacteria responsible for causing a common disease in pond-raised channel catfish.
1. Biofloc technology systems reduce the intensity of common off-flavors in channel catfish. Preharvest off-flavors described as “earthy-musty” in catfish produced in earthen ponds continue to hamper the growth of this industry. An ARS researcher at University, Mississippi, in collaboration with an ARS researcher at Stuttgart, Arkansas, and a scientist at University of Arkansas-Pine Bluff, Arkansas, found that the intensity of earthy-musty off-flavor problems were reduced in catfish grown in outdoor biofloc technology systems. These biofloc technology systems inhibited the growth of the common types of blue-green algae responsible for producing earthy and musty compounds that can occur in catfish production ponds. The discovery of this benefit of the biofloc technology systems provides producers with an alternative to using earthen ponds to grow catfish in order to reduce off-flavor delayed harvests and provide a good-tasting, high-quality product to consumers. A decrease in off-flavor delayed harvests directly benefits producers by reducing economic losses associated with additional feeding costs and loss of fish to disease and water quality problems incurred during delayed harvests.
Nanayakkara, N., Schrader, K. 2011. Evaluation of free radical-generating compounds for toxicity towards the cyanobacterium Planktothrix perornata which causes musty off-flavor in pond-raised channel catfish (Ictalurus punctatus). Aquaculture Research. 42:1895-1898.