Seasonal Variation of Off‐Flavours in a Full‐Scale Recirculating Aquaculture System Rearing Rainbow Trout Oncorhynchus mykiss : A Case Study

Recirculating aquaculture system (RAS) is a promising strategy for economically and environmentally sustainable fish farming. Unfortunately, microorganisms in an RAS may produce off-flavours that accumulate in fish flesh and reduce consumer attraction for aquaculture-produced fish. Traditionally, geosmin (GSM) and 2-methylisoborneol (MIB), the compounds causing musty and earthy flavour, have been the most studied off-flavour compounds, but lately other compounds have also been considered important subjects of study. So far, only a little is known about the formation of different compounds at an RAS farm and their concentrations’ fluctuations during the seasons. This case study aimed at monitoring the changes in off-flavour concentrations in different locations of a full-scale (1 M kg a−1) RAS farm rearing rainbow trout (Oncorhynchus mykiss). Off-flavours were measured in fish, in recirculating water and in the inlet water throughout a year. Some of the compounds were introduced to the RAS via inlet water, whereas others were formed at the farm, mostly ranging from 0 to 30 ng L−1. The concentrations of GSM and MIB were below 20 ng L−1 and in most cases below 10 ng L−1, whereas methional peaked up to 70 ng L−1 in the fall and winter. In fish, the concentrations mainly remained below 600 ng kg−1 but occasionally MIB peaked up to 1900 ng kg−1. The results highlight the need for sufficient treatment of inlet water even in the winter to maintain suitable conditions to produce fish of high quality.