64 JUNE 2023 • WORLD AQUACULTURE • WWW.WAS.ORG lower defense activity, and more optimal environmental conditions for fish. Further, Quantidoc has developed a formula to calculate “defense activity” and the results from this formula clearly indicate the same results (Fig. 2). Gilthead Seabream Testing was conducted by ArDag Ltd. at Eilat, Israel, using gilthead seabream Sparus aurata starting at 2 g for 45 days. The objective was to compare BioFishency ELX™ water treatment vs. a water flow-through system by comparing the fish growth rate and health and welfare parameters. Growth, survival and feed conversion were similar between the two systems (Table 2, Fig. 3). Rainbow Trout Testing was conducted at the BioFishency’s R&D facility (Acre, Israel) using rainbow trout Oncorhynchus mykiss starting at 475 g for 50 days. The objectives were to demonstrate grow-out of rainbow trout in saline water and to evaluate the effect on product quality using a sensory panel. Rainbow trout (475 g) were stocked at 95 kg/m3 in a Biofishency ELX system. The final weight was 724 g, with a growth rate of 0.84 percent/d or 5.0 g/d. The objectives were to quantify the purging effect on water and fish tissue. Secondary metabolites of several microorganisms, which lead to unsavory off-flavor and odor of the fish, result in severe economic losses and negative reputation to the RAS industry. As a mitigation strategy for the off-favor problem, RAS operators typically perform a purging (flushing) step prior to marketing. The purging process aims at eliminating the off-flavor agents that accumulate in fish tissues during grow-out. Performed in separate purging tanks, fish are held under a flow-through regime. The purging process is based on maintaining negligible concentrations of the off-flavor agents in the water, thereby promoting diffusion of chemicals from fish tissues to the water. In contrast to the grow-out period, purging is performed under starvation and requires vast quantities of water for exchange. During purging, which normally requires 7-14 days, the fish lose ~5 percent of their weight, thereby decreasing farmers’ revenue. Purging has become a bottleneck for the development of the RAS industry in general, and specifically for growing fish species (e.g., Atlantic salmon) away from their native climate and natural water sources. This is especially relevant in coldwater species, where the diffusion of the off-flavor compounds from fish flesh to clean water is relatively slow. During the trial, fish were exposed to water spiked with 750 ng/L of MIB and geosmin, after which the BioFishency ELX™ system was introduced during the purging, while continuing to feed fish. Within five days, all MIB in the water had been removed, while in seven days, the system efficiently oxidized geosmin. High uptake by the fish muscle of both MIB and geosmin was measured after the spiking (670 and 750 ng/kg, respectively). In just seven days, MIB was not detected in the fish flesh, and within ten days, geosmin was fully removed from skin and muscles. The results of this study indicated that MIB and geosmin can be fully eliminated with BioFishency ELX™ in less than ten days, while fish can continue growing regularly during the depuration period and no extra water discharge is required. In practice, by using the Biofishency ELX a given RAS facility may shorten the time to market, prevent fish biomass loss and increase annual revenue by at least 5 percent. Notes Igal Magen, Co-Founder & CTO BioFishency References Ben-Asher, R., Y. Gendel and O. Lahav. 2023. Electrochemical applications in RAS: a review. Reviews in Aquaculture 2023:1-20. Ben-Asher, R. and O. Lahav. 2016. Electrooxidation for simultaneous ammonia control and disinfection in seawater recirculating aquaculture systems. Aquaculture Engineering 7273:77-87. Gendel, Y. and O. Lahav. 2012. Revealing the mechanism of indirect ammonia electrooxidation. Electrochimica Acta 63:209-219. Graham, D.W., C.W. Knapp, E.S. van Vleck, K. Bloor, T.B. Lane, C.E. Graham. 2007. Experimental demonstration of chaotic instability in biological nitrification. ISME Journal 1:385-393. Lindholm-Lehto, P.C. and J. Vielma. 2019. Controlling of geosmin and 2-methylisoborneol induced off-flavors in recirculating aquaculture system farmed fish—A review. Aquaculture Research 50:9-28. Marinčić, L. and F.B. Leitz. 1978. Electro-oxidation of ammonia in waste water. Journal of Applied Electrochemistry 8:333-345. Pinfold, G. 2014. Feasibility of land-based closed-containment Atlantic salmon operations in Nova Scotia. Submitted to the Nova Scotia Department of Fisheries and Aquaculture by Gardner Pinfold Consultants, Inc. FIGURE 3. Growth rate of gilthead sea bream grown in a BioFishency ELXTM system compared to a flow-through system. The results of this study indicated that MIB and geosmin can be fully eliminated with BioFishency ELX™ in less than ten days, while fish can continue growing regularly during the depuration period and no extra water discharge is required. In practice, by using the Biofishency ELX a given RAS facility may shorten the time to market, prevent fish biomass loss and increase annual revenue by at least 5 percent.
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