Fatty acid metabolism (desaturation, elongation and beta-oxidation) in rainbow trout fed fish oil- or linseed oil-based diets.

ABSTRACT

In consideration of economical and environmental concerns, fish oil (FO) substitution in aquaculture is the focus of many fish nutritionists. The most stringent drawback of FO replacement in aquafeeds is the consequential modification to the final fatty acid (FA) make-up of the fish fillet. However, it is envisaged that a solution may be achieved through a better understanding of fish FA metabolism. Therefore, the present study investigated the fate of individual dietary FA in rainbow trout (Oncorhynchus mykiss) fed a FO-based diet (rich in 20 5n-3) or a linseed oil-based diet (LO; rich in 18 3n-3). The study demonstrated that much of the 18 3n-3 content from the LO diet was oxidised and, despite the significantly increased accretion of Delta-6 and Delta-5 desaturated FA, a 2- and 3-fold reduction in the fish body content of 20 5n-3 and 22 6n-3, respectively, compared with the FO-fed fish, was recorded. The accretion of longer-chain FA was unaffected by the dietary treatments, while there was a greater net disappearance of FA provided in dietary surplus. SFA and MUFA recorded a net accretion of FA produced ex novo. In the fish fed the FO diet, the majority of dietary 20 5n-3 was accumulated (53.8 %), some was oxidised (14.7 %) and a large proportion (31.6 %) was elongated and desaturated up to 22 6n-3. In the fish fed the LO diet, the majority of dietary 18 3n-3 was accumulated (58.1 %), a large proportion was oxidised (29.5 %) and a limited amount (12.4 %) was bio-converted to longer and more unsaturated homologues.