Recirculating aquaculture systems (RAS) have become increasingly popular in recent years, especially in Europe. Advantages by RAS are (1) reduced water consumption and land use to meet environmental regulations in many countries; (2) better control of feed allocations and of biotic and abiotic parameters to ensure a stable and standardized fish production; (3) improved treatment of waste with options to produce valuable fertilizers. Relative to other fisheries, RAS can produce the highest yield per unit area with the smallest environmental footprint, depending on aquaculture feeds and non-renewable energy consumption. Most RAS systems use natural freshwater or seawater in the production tanks. This means that naturally occurring bacteria will be part of the RAS microflora in both the water and on surfaces in tanks and biofilters in RAS farms. Among naturally occurring aquatic bacteria are several species that release earthy- and musty-smelling volatile compounds, and some of these microbes appear to thrive in RAS facilities. The off-flavours may taint fish after uptake through gills and other surfaces and impact both the sensory quality and market value of the fish. Consequently, RAS farmers must avoid accumulation of these compounds in the fish.
A search on Web of Science shows that although the first articles on “aquaculture and recirculation” appeared in 1974, the first article on “fish and off-flavour” already occurred in 1949 (Cook et al., Food Research 14:449-459) in a study on flavours in fish meal. Since then, a growing number of articles have treated off-flavour issues in farmed fish (see below).
In the presentation at LACQUA24, experiences from 20 years of off-flavour research in the aquaculture production in Denmark are given. Further, recent knowledge on off-flavour producers and concentration levels of off-flavours in RAS will be presented. Finally, potential procedures for elimination and mitigation of these compounds will be given.