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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: Effects of swimming speed and dissolved oxygen on geosmin depuration from market-size Atlantic salmon Salmo salar

item DAVIDSON, JOSH - Freshwater Institute
item SUMMERFELT, STEVEN - Superior Fresh
item Grimm, Casey
item FISCHER, GREGORY - University Wisconsin-Stevens Point-northern Aquaculture Demonstration Facility
item GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2021
Publication Date: 10/8/2021
Citation: Davidson, J.W., Summerfelt, S., Grimm, C.C., Fischer, G., Good, C. 2021. Effects of swimming speed and dissolved oxygen on geosmin depuration from market-size Atlantic salmon Salmo salar. Aquacultural Engineering. 95:102201.

Interpretive Summary: Failure to remediate earthy off-flavors, such as geosmin, from Atlantic salmon produced in recirculating aquaculture systems (RAS) can result in rejected product and economic loss. As such, RAS facilities generally relocate fish to finishing systems where feed is withheld for 6-14 days and clean water is added to flush these unpalatable compounds, a process known as depuration. Nevertheless, extended duration of this procedure has drawbacks including fish weight loss and increased water and energy use; therefore, refinements that shorten the depuration period would be beneficial to salmon producers. Procedural aspects that increase gill ventilation rate, for example, could increase the rate of off-flavor excretion. Accordingly, a study was conducted to investigate the potential for increased swimming speed and reduced oxygen levels to speed off-flavor removal from market-size Atlantic salmon. Two fish swimming speeds (0.3 and 0.6 body lengths/second) dictated by water velocity and two oxygen levels (90 or 100% O2 saturation) were tested in replicated systems. In short, significant effects of the tested variables were not observed suggesting that fish swimming speeds and oxygen levels within the tested range will not improve off-flavor removal from Atlantic salmon or shorten the depuration period. These findings provide added guidance for establishment and refinement of off-flavor remediation procedures at salmon RAS facilities.

Technical Abstract: Common off-flavor compounds, including geosmin (GSM) and 2-methylisoborneol (MIB), bioaccumulate in Atlantic salmon Salmo salar cultured in recirculating aquaculture systems (RAS) resulting in earthy and musty taints that are unacceptable to consumers. To remediate off-flavor from market-ready salmon, RAS facilities generally relocate fish to separate finishing systems where feed is withheld and makeup water with very low to nondetectable GSM and MIB levels is rapidly exchanged, a process known as depuration. Several procedural aspects that affect salmon metabolism and the associated rate of off-flavor elimination, however, have not been fully evaluated. To this end, a study was carried out to assess the effects of swimming speed and dissolved oxygen (DO) concentration on GSM levels in water and fish flesh during a 10-day depuration period. Atlantic salmon (5-8 kg) originally cultured in a semi-commercial-scale RAS (150 m3 tank) were exposed to a concentrated GSM bath before being transferred to 12 replicated partial reuse depuration systems (5.4 m3 total volume). Two swimming speeds (0.3 and 0.6 body lengths/sec) and two DO levels (90 and 100% O2 saturation) were applied using a 2x2 factorial design (N=3), and each system was operated with a 5-h hydraulic retention time, creating a water flushing to biomass ratio of 151 L/kg fish biomass/day. Geosmin was assessed at Days 0, 3, 6, and 10 in system water and salmon flesh. A borderline effect (P= 0.064; 0.068) of swimming speed was measured for water and fish, respectively, at Day 3, where slightly lower GSM was associated with low swimming speed (0.3 body lengths/sec); however, differences were not detected at Days 6 or 10 when salmon are commonly removed for slaughter. Overall, this research indicates that significant improvements in GSM depuration from RAS-produced Atlantic salmon are not expected when purging with swimming speeds and DO concentrations similar to those tested during this trial.