Growth and Depuration of Off-Flavors in Rainbow Trout Oncorhynchus Mykiss in a Partial Recirculating Aquaculture System (PRAS)

In recirculating aquaculture systems (RAS), off-flavours accumulated in fish muscle tissue can be problematic in terms of consumer acceptance and the reputation of farmed fish products. Off-flavours often give fish earthy, muddy, or other undesirable flavours. Typically, off-flavours are removed during a depuration period in which fish are fasted and held in clean water. Unfortunately, this causes additional costs and delayed sales, while fish lose weight and show a decrease in lipid content. First, we studied fish growth in a partial RAS (PRAS) where the conditions are very similar to those in depuration with a water exchange rate of 4000 L kg⁻¹ feed, compared to RAS with a 650-L water kg⁻¹ feed. Rainbow trout (Oncorhynchus mykiss) was reared in both systems. Our aim was to combine the benefits of a higher water exchange rate: the lack of need for biofilters and a lower accumulation of off-flavours while obtaining stable rearing conditions. Additionally, we studied the effects of moderate feeding and H₂O₂ addition during depuration. The fish grew faster in a PRAS than in a RAS when fed ad libitum. Thirteen off-flavour compounds were found in the fish flesh and 11 in the circulating water. The H₂O₂ addition led to decreased levels of off-flavours in the tank water and in fish muscle. The results showed no significant differences in off-flavours between the fed and not-fed systems, showing that moderate feeding did not prevent a good depuration result. However, the lipid content and the overall fish weight were higher in the fed systems, which suggests more effective depuration. Increased depuration efficiency can be an important tool when considering ways to improve the profitability of production.