|DAVIDSON, JOHN - Freshwater Institute|
|SWIFT, BRUCE - Tri-Gen Fish Improvement Ltd|
|RUAN, ERIC - Lacombe Research Centre|
|AALHUS, JENNIFER - Lacombe Research Centre|
|JUAREZ, MANUAL - Lacombe Research Centre|
|GOOD, CHRIS - Freshwater Institute|
|SUMMERFELT, STEVEN - Freshwater Institute|
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/18/2013
Publication Date: 2/11/2014
Citation: Davidson, J., Schrader, K., Swift, B., Ruan, E., Aalhus, J., Juarez, M., Good, C., Wolters, W.R., Burr, G.S., Summerfelt, S. 2014. Evaluation of depuration procedures to mitigate off-flavor from harvest size Atlantic Salmon Salmo Salar cultured in a land-based recirculating aquaculture system. Aquaculture America Conference.
Technical Abstract: Fish cultured within water recirculating aquaculture systems (RAS) can develop “earthy” or “musty” off-flavors in their flesh due to the bioaccumulation of the compounds geosmin and 2-methylisoborenol (MIB), respectively, that are produced by certain bacteria (e.g., actinomycetes). These bacteria and compounds are also present in system biofilms. As a general practice, salmonids cultured in RAS are transferred to separate depuration systems with odor-free water to purge these unpalatable flavors. Technologies and standard operating practices that optimize purging kinetics for Atlantic salmon Salmo salar and other species cultured in RAS are needed to improve the reliability and consistency of depuration. Atlantic salmon cultured within a partial reuse system to 1-2 kg (Study 1) and a semi-commercial scale RAS with a 150 m3 tank to 3-5 kg (Studies 2 and 3) were stocked within 12 identical partial reuse systems (0.5 m3) for three 2 x 2 factorial depuration trials evaluating: 1) hydrogen peroxide (H2O2) disinfection and granular activated carbon (GAC) filtration of the makeup flow; 2) the same treatments as Study 1 but with larger salmon; and 3) H2O2 disinfection of the depuration system and presence/absence of water aeration media. Prior to each study, the depuration systems were used for rainbow trout Oncorhynchus mykiss culture to establish biofilm on system surfaces and a realistic worst-case-scenario for purging. Fish were kept off feed during the depuration period. Six salmon were harvested from the original culture systems on Day 0 and filleted for baseline assessment of off-flavor concentrations. Thereafter, fillet and water samples were taken at daily intervals from the depuration systems up to Day 10 to evaluate off-flavor kinetics. During Study 1, off-flavor concentrations increased for all treatments, emphasizing the need to begin with clean, biofilm-free depuration systems. Study 2 indicated that pre-treatment of systems with H2O2 combined with GAC filtration of the makeup water resulted in the greatest reduction of off-flavor levels in the culture water and salmon fillets. However, H2O2 disinfection alone appeared to be just as effective. Study 3 demonstrated that depuration systems that are disinfected with H2O2 and absent of aeration media were the most effective at purging off-flavor from salmon compared to control systems that were not disinfected and contained aeration media. These studies demonstrated that the depuration process for Atlantic salmon cultured to harvest size in RAS can be optimized when using standard operating procedures that provide clean and relatively biofilm-free systems. Aeration media should not be used within depuration systems because of the challenges posed for effective cleaning, disinfection, and inactivation of off-flavor bacteria and compounds present in the biofilms. In addition, pre-disinfection of depuration systems using 250 mg/L H2O2 appears to enhance off-flavor removal.