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Research Project: Support the Viability and Expansion of Land-Based Closed-Containment Aquaculture

Location: Cool and Cold Water Aquaculture Research

Title: Water quality, waste production, and off-flavor characterization in a depuration system stocked with market-size Atlantic salmon Salmo salar

Author
item DAVIDSON, JOHN - Freshwater Institute
item REMAN, NATALIE - Freshwater Institute
item CROUSE, CURTIS - Freshwater Institute
item VINCI, BRIAN - Freshwater Institute

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2022
Publication Date: 9/8/2022
Citation: Davidson, J.W., Reman, N., Crouse, C., Vinci, B. 2022. Water quality, waste production, and off-flavor characterization in a depuration system stocked with market-size Atlantic salmon Salmo salar. Journal of the World Aquaculture Society. (54)1:96-112. https://doi.org/10.1111/jwas.12920.
DOI: https://doi.org/10.1111/jwas.12920

Interpretive Summary: Land-based aquaculture facilities that grow market-size Atlantic salmon use a finishing process called depuration to eliminate earthy, muddy off-flavors from fish. During this procedure, feed is withheld and large volumes of water are flushed. To maximize available resources, water passing through depuration systems is often reused in other fish production systems. In other cases, this water is discharged from the facility. Both approaches require an understanding of solids and nutrient content for waste treatment decisions and complicance with local discharge standards; however, these data were lacking. As such, a study was carried out to characterize water quality, waste production, and off-flavor in Atlantic salmon during a 7-day depuration period. Results showed that residual waste production occurs in depuration systems. Solids, phosphorus, and nitrogen levels spiked after fish were stocked, and concentrations declined thereafter. Total ammonia nitrogen levels stabilized suggesting that salmon began to metabolize fat reserves. These novel findings are expected to guide procedural refinements at land-based Atlantic salmon facilities including adoption of methods to eliminate residual wastes when water is reused. The results also serve as a reference for expected discharge from Atlantic salmon depuration systems which will guide pollution control measures and faciliate regulatory compliance.

Technical Abstract: Land-based Atlantic salmon, Salmo salar, grow-out facilities utilize depuration to remediate earthy, musty taints associated with the off-flavor compounds geosmin (GSM) and 2-methylisoboreol (MIB). During this process, fish are transferred to clean systems where water low or void of off-flavor is rapidly exchanged while withholding feed. Water used during depuration is either repurposed as supply water in recirculating aquaculture systems (RAS) or discharged from facilities. Both approaches require an understanding of water quality and waste production for water treatment decisions and compliance with pollution discharge standards; however, these data were lacking. Therefore, a study was carried out to characterize these parameters in depuration systems operated using commercially relevant procedures for market-size Atlantic salmon. To begin, 311 salmon (5 –6 kg) originally cultured in freshwater RAS were moved to an 18 m3 depuration tank. Feed was withheld one day before fish transfer and throughout the 7-day depuration period. Hours after stocking, total suspended solids (TSS), total phosphorus (TP), and total ammonia nitrogen (TAN) levels spiked, and waste concentrations began to decline thereafter. Delta TSS and TP were negligible by the end of the trial; however, TAN plateaued indicating that salmon began to catabolize somatic tissue in the absence of feeding. Daily waste production per kg fish ranged as follows: 35–265 mg TSS, 1.2–15.0 mg TP, and 35–59 mg TAN. Additionally, GSM and MIB levels in water and fish were low throughout the study, i.e., < 1.5 ng/L and < 60 ng/kg, respectively. This research indicates that residual waste production occurs while depurating Atlantic salmon. Procedural refinements and engineering recommendations were also gleaned including optimized locality for introducing depuration system water within RAS and proposed extension of the feed withholding period before depuration.