Earthy and musty off-flavours caused by the microbial metabolites geosmin (GSM) and 2-methylisoborneol (MIB) remain a significant challenge for land-based salmon producers.
These compounds give rise to unpleasant flavours in fish produced in recirculating aquaculture systems (RAS) and can lead to negative consumer perception, reduced product prices and lower revenues when detected in fillets.
New research led by John Davidson and Curtis Crouse from The Conservation Fund’s Freshwater Institute has examined the effect that RAS maturation has on the production of these substances that affect the flavour of salmon.
Until now, the only effective method for removing them has been depuration prior to harvest, although this remains a remediation solution that increases costs, labour requirements and water use.
The study compared RAS, operated continuously for 2.5 years, with disinfected and restarted immature systems shows that microbial maturity significantly attenuates off-flavour formation. In immature units, waterborne GSM and MIB peaked at 35–40 ng/L, while mature systems maintained concentrations under 13 ng/L.
Fillet levels mirrored these trends. At two months, GSM reached 696 ± 31 ng/kg in immature systems, compared with 247 ± 30 ng/kg in mature ones. The study concludes: “Ultimately, the microbially mature RAS minimized off-flavor in water and salmon flesh.”
The authors found that off-flavour issues were not driven by the quantity of off-flavour-producing microbes. They report that “the abundance of off-flavor-producing organisms was not associated with off-flavor trends.” Instead, immature systems showed higher levels of ammonia, nitrite, suspended solids, heterotrophic bacteria and, notably, higher “true color”, a parameter linked to dissolved organic matter.
Machine-learning analysis identified true color as “the most important feature affecting GSM”, while total phosphorus and suspended solids were key factors influencing MIB. In contrast, mature systems maintained more stable nitrification and microbial composition, conditions that supported consistently lower off-flavour production.
For RAS operators, the findings highlight a practical, preventive strategy: maintain long-term system continuity and avoid disruptions that reset biofilters. Stable, mature microbiomes delivered more efficient nutrient conversion and far less fluctuation in microbial communities, which in turn helped suppress GSM and MIB.
Limiting off-flavour formation within the grow-out system could reduce dependence on depuration, a process that requires additional tanks, water and fasting and ultimately lowers operational efficiency. As the authors note, maintaining favourable microbial and water-quality conditions may offer “a less complicated, lower-cost solution to this industry challenge.”
Reference:
Davidson, John, Crouse, Curtis, Lepine, Christine, Ranjan, Rakesh, Stangroom, Julianna, Poley, Jordan, and Good, Christopher (2025). Comparing off-flavor trends in freshwater recirculating aquaculture systems with microbially mature or immature biofilters while growing Atlantic salmon Salmo salar. Journal of the World Aquaculture Society, 56:e70067. DOI: 10.1111/jwas.70067
Latest news
-
-
Morocco advances its goal of making marine aquaculture a priority drive of blue growth
Rabat, Morocco, 10 December 2025 | The National Council for Marine Aquaculture reviews regulatory progress and steps to ensure the implementation of sector-specific legislation
-
Cooke’s new offer delays the approval of the AVRAMAR Greece restructuring plan
Athens, Greece, 10 December 2025 | Creditors have postponed submitting the file to the court, citing both the need to update the technical documentation and the possibility of reconsidering the agreement reached with Aqua Bridge
