Depuration system flushing rate affects geosmin removal from market-size Atlantic salmon Salmo salar

Authors: DAVIDSON, JOHN - Freshwater Institute; GRIMM, CASEY - US Department Of Agriculture (USDA); SUMMERFELT, STEVEN - Superior Fresh; FISCHER, GREGORY - University Of Wisconsin; GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2020
Publication Date: 7/7/2020
Citation: Davidson, J., Grimm, C., Summerfelt, S., Fischer, G., Good, C. 2020. Depuration system flushing rate affects geosmin removal from market-size Atlantic salmon Salmo salar. Aquacultural Engineering. 90. Article 102104. https://doi.org/10.1016/j.aquaeng.2020.102104.
DOI: https://doi.org/10.1016/j.aquaeng.2020.102104

Interpretive Summary: Common off-flavor compounds bioaccumulate in fish cultured in recirculation aquaculture systems (RAS) resulting in earthy tastes that are objectionable to consumers. In response, most salmon RAS facilities relocate fish from production tanks to separate depuration or "purge" systems as a method to remediate off-flavor. However, optimal water flushing rates had not been previously characterized for these systems. As such, a study was carried out to evaluate the effectiveness of three water flushing rates for removing off-flavor from market-size Atlantic salmon previously cultured in RAS. Lowest off-flavor levels were achieved in purge systems that utilized rapid water flushing with complete system water exchange taking place in 2.4-4.6 hours. Overall, this research will help the growing land-based RAS sector develop effective standard operating procedures that ensure that market-ready fillets are free of earthy/musty off-flavors, enabling positive consumer perception of these products. Water use and energy savings associated with optimized water pumping could also be achieved by salmon producers based on this research.

Technical Abstract: Common off-flavor compounds including geosmin (GSM) bioaccumulate in fish cultured in recirculation aquaculture systems (RAS) resulting in unpalatable fillets that are objectional to consumers. Most RAS facilities relocate fish from grow-out tanks to separate depuration systems with increased water flushing to remediate pre-harvest off-flavors, but certain aspects of this procedure have not been optimized including characterization of water exchange rates that effectively diminish off-flavor. To this end, a study was carried out to evaluate the effects of water flushing rate and associated depuration system hydraulic retention time (HRT) on the kinetics of GSM removal from Atlantic salmon Salmo salar originally produced in a semi-commercial scale freshwater RAS. Twenty-six fish (5-7 kg each) were stocked into twelve replicate depuration systems operated with system HRTs of 2.4, 4.6, and 11.3-h, respectively (N=4). Geosmin was assessed at intervals in system water and fish flesh over a 10-day feed withholding period. Waterborne GSM concentration was affected by flushing rate and associated system HRT (P< 0.05). Depuration systems operated with an 11.3-h HRT had greater waterborne GSM levels at 3, 6, and 10 days post-stocking compared to 2.4 and 4.6-h HRT. A similar trend was generally reflected in salmon flesh. Residual GSM levels were successively higher in fillets from depuration systems with increasingly longer HRT at Day 6. Geosmin was greatest in salmon flesh from the 11.3-h HRT treatment on Day 10, but there was no difference in fillet GSM between the 2.4 and 4.6-h HRT at the end of the trial. This research indicates that lowest residual GSM is achieved in depuration systems with increased water flushing and shorter HRT, i.e., 2.4 to 4.6-h under conditions of this study. Selection of optimal flushing rate to remediate off-flavor from RAS-produced Atlantic salmon may also be dictated by water and energy use metrics and site-specific water availability among other factors.