Location: Natural Products Utilization Research
2018 Annual Report
Objectives
1. Develop management strategies to mitigate pre-harvest microbial-derived off-flavors in fish cultured in recirculating aquaculture systems (RAS) to reduce off-flavor delayed harvest.
2. Discover and develop management strategies to mitigate pre-harvest microbial-derived off-flavors in fish cultured in outdoor earthen ponds to reduce off-flavor delayed harvest.
2.A. Evaluate and identify the impact of split-pond production practices in reducing or enhancing the incidences and intensities of common pre-harvest off-flavors in channel catfish.
2.B. Further evaluation of biofloc technology (BFT) production systems for the benefits in managing common pre-harvest off-flavors in cultured finfish.
2.C. Evaluation of a biocontrol approach in reducing the abundance of common off-flavor producing cyanobacteria in catfish production ponds.
Approach
Develop management strategies to mitigate pre-harvest microbial-derived off-flavors in fish cultured in recirculating aquaculture systems (RAS) to reduce off-flavor delayed harvest. Discover and develop management strategies to mitigate pre-harvest microbial-derived off-flavors in fish cultured in outdoor earthen ponds to reduce off-flavor delayed harvest. Evaluate and identify the impact of split-pond production practices in reducing or enhancing the incidences and intensities of common pre-harvest off-flavors in channel catfish. Further evaluation of biofloc technology (BFT) production systems for the benefits in managing common pre-harvest off-flavors in cultured finfish. Evaluation of a biocontrol approach in reducing the abundance of common off-flavor producing cyanobacteria in catfish production ponds.
Progress Report
Preharvest off-flavors such as “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 certain off-flavor compounds in the fish flesh, and certain bacteria are attributed as the main producers of these off-flavor compounds in RAS. Various concentrations of ammonium chloride were evaluated to determine effects on biomass and off-flavor compound production by one type of bacteria which produces the earthy and musty off-flavor compounds. Similar biomass production occurred at the different ammonium chloride concentrations throughout most of the study period. Conversely, significantly higher concentrations of earthy and musty off-flavor compounds were produced at the highest ammonium chloride test concentration. These preliminary results indicate that maintenance of total ammonia nitrogen concentrations below 1 mg/L may reduce concentrations of earthy and musty off-flavor compounds in the water of RAS and subsequently reduce the intensities of these types of off-flavor episodes.
Accomplishments
1. Management practices for pre-harvest off-flavors of catfish raised in split-ponds. The interest and use of variations of partitioned aquaculture systems (PAS) by the southeastern U.S. catfish farming industry continues to grow, and split-pond systems, one type of PAS, are designed to improve management of dissolved oxygen levels and fish waste products (e.g., ammonia) compared to conventional earthen ponds that have been used for many decades. While many have assumed that fish off-flavor incidence will be reduced in split-ponds because previous research showed that off-flavors were rare in fish grown in PAS, there has not been any assessment of the occurrences and intensities of common “off-flavor” episodes in split-pond systems. During a multi-year study, ARS researchers at Oxford, Mississippi, and Stoneville, Mississippi, evaluated water and catfish fillet samples collected from commercial and research split-ponds located in west Mississippi and west Alabama for intensities of earthy and musty off-flavor compounds while phytoplankton ecology of the split-ponds was also determined. Concentrations of earthy and musty compounds in fillets and the description and intensities determined via sensory analysis were similar to those reported previously for off-flavor catfish from conventional ponds. In addition, the types of phytoplankton and community structures observed in the split-ponds were not different from those commonly observed in conventional catfish ponds. These results demonstrate that farmers using split-ponds will use the same management approaches and preharvest sampling of catfish to monitor for the presence of off-flavors as those used for dealing with earthy and musty off-flavor problems in catfish raised in conventional ponds (e.g., applications of algicides). These determinations are of critical importance to commercial culturists who are considering the benefits and constraints of adopting split-pond technology.
