Abstract
Nutritional strategies are currently developed to produce farmed fish rich in n-3 long-chain PUFA (LC-PUFA) whilst replacing fish oil by plant-derived oils in aquafeeds. The optimisation of such strategies requires a thorough understanding of fish lipid metabolism and its nutritional modulation. The present study evaluated the fatty acid bioconversion capacity of rainbow trout (Oncorhynchus mykiss) fry previously depleted in n-3 PUFA through a 60-d pre-experimental feeding period with a sunflower oil-based diet (SO) followed by a 36-d experimental period during which fish were fed either a linseed oil-based diet (LO) (this treatment being called SO/LO) or a fish oil-based diet (FO) (this treatment being called SO/FO). These treatments were compared with fish continuously fed on SO, LO or FO for 96 d. At the end of the 36-d experimental period, SO/LO and SO/FO fish recovered >80 % of the n-3 LC-PUFA reported for LO and FO fish, respectively. Fish fed on LO showed high apparent in vivo elongation and desaturation activities along the n-3 biosynthesis pathway. However, at the end of the experimental period, no impact of the fish n-3 PUFA depletion was observed on apparent in vivo elongation and desaturation activities of SO/LO fish as compared with LO fish. In contrast, the fish n-3 PUFA depletion negatively modulated the n-6 PUFA bioconversion capacity of fish in terms of reduced apparent in vivo elongation and desaturation activities. The effects were similar after 10 or 36 d of the experimental period, indicating the absence of short-term effects.
Highlights
There is an expectation on aquaculture to supply fish rich in health promoting n-3 long-chain PUFA (n-3 LC-PUFA), principally EPA (20 : 5n-3) and DHA (22 : 6n-3)
The present study evaluated the fatty acid bioconversion capacity of rainbow trout (Oncorhynchus mykiss) fry previously depleted in n-3 PUFA through a 60-d pre-experimental feeding period with a sunflower oil-based diet (SO) followed by a 36-d experimental period during which fish were fed either a linseed oil-based diet (LO) or a fish oil-based diet (FO)
The SO/LO and SO by FO (SO/FO) final fish weights were higher than those of fish fed on SO for 96 d, but did not reach those of fish constantly fed on LO and FO for 96 d (Fig. 1)
Summary
There is an expectation on aquaculture to supply fish rich in health promoting n-3 long-chain PUFA (n-3 LC-PUFA), principally EPA (20 : 5n-3) and DHA (22 : 6n-3). Previous studies reported increased desaturation and elongation activities without significant detrimental effects to growth and health in salmonids fed on plant-derived oil diets (i.e. sunflower oil[14,15,16], olive oil[14], palm oil[16], rapeseed oil[16,17] or linseed oil[14,15,17,18]), as a blend or sole source. An alternative strategy involves stimulating fish fatty acid metabolism through nutritional programming during early larval stages as a means of improving the acceptance and conversion of dietary ALA from plant-based diets at juvenile stages[31,32,33]. Vagner et al[31] observed increased Δ-6 desaturase gene expression in European sea bass juveniles fed an n-3 LC-PUFA deficient diet from day 83 post-hatch to day 118, when larvae had been previously fed a low n-3 LC-PUFA diet
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