A n-3 PUFA depletion applied to rainbow trout fry (Oncorhynchus mykiss) does not modulate its subsequent lipid bioconversion capacity

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.

Keywords: ALA α-linolenic acid; CD coefficient of distance; DGC daily growth coefficient; FE feed efficiency; FO fish oil-based diet; LA linoleic acid; LC-PUFA long-chain PUFA; LO linseed oil-based diet; SO sunflower oil-based diet; SO/FO SO until day 60 and then FO from days 61–96; SO/LO SO until day 60 and then LO from days 61–96; Fatty acid metabolism; Lipid bioconversion capacity; Plant-derived oils; Rainbow trout; Whole body fatty acid balance method.

Fig. 1

Mean weight (g/fish) of rainbow trout at each sampling time point over the 60-d pre-experimental period and the 36-d experimental period. Values are means (n 3 except sunflower oil-based diet (SO) treatment from starting day until day 60 for which n 9), with their standard errors. The fish weight was impacted by the dietary treatment regarding the lowest weight of fish fed SO (■) and the highest weights of fish fed on linseed oil–based diet (LO, ●) or fish oil-based diet (FO, ▲) during 96 d. Intermediate fish weights were reported when feeding fish on SO for 60 d and then on LO (SO/LO, ○) or FO (SO/FO, Δ) for 36 d. ^a,b,c Mean values with unlike superscript letters were significantly different (Tukey’s post hoc test, α 5 %).