Regulation of the ω-3 fatty acid biosynthetic pathway and fatty acids bioconversion capacity in selected rainbow trout (Oncorhynchus mykiss) using alternative dietary oils

Abstract

Currently, vegetable oils (VO) have become the primary alternative for fish oil (FO), as they are readily available, cost effective ingredients that contain high levels of essential C18 fatty acids (FA). Through a selective breeding program we have developed rainbow trout (Oncorhynchus mykiss) families which are improved in their ability to desaturate and elongate α-linolenic acid (18:3n-3; ALA) to produce the n − 3 long-chain polyunsaturated fatty acids [LC-PUFA, eicosapentaenoic acid (20:5n-3; EPA), docosahexaenoic acid (22:6n-3; DHA)]. Therefore, we investigated the influence of fish oil (FO) and alternative oil sources [linseed (LO), soy (SO), canola (CO), coriander (CNO) and algae (AO), all of which include various levels of ALA, linoleic acid, oleic acid, and DHA FAs] on growth, muscle tissue FA composition, and lipid-related hepatic gene expression in trout. Six experimental diets (D1: 17 %FO; D2:17 %LO; D3:8.5 %LO +2.83 %SO + 2.83 %CO + 2.83 %CNO; D4: 4.25 %SO + 4.25 %CO +8.5 %CNO; D5: 8.5 %LO + 8.5 %AO; D6: 17 %AO, percentage is referring to g/kg as fed) were formulated and fed in triplicate to selected trout (initial average weight 470 ± 30 g fish^{− 1}) for 10 weeks. The highest growth performance was observed in AO fed group (D6) whereas lowest value was found in D4. Total saturated FA in muscle was affected by oil sources; diets with LO, SO, CO and CNO exhibited lower deposition than other oil sources. Among VO sources, highest EPA deposition was found in D5 (AO+LO; 1.74 %) and was similar to D2 (LO; 1.61 %), whereas lowest value in D4 (1.26 %) which was similar to D3 (1.45 %). Highest and lowest muscle content of PUFAs was observed in D2 and D4 respectively. Total EPA and DHA content were highest in D6 which is almost three times higher than D2 fed group. The highest expression levels of PPARG, SREBP2 and FADS6 (genes involved in biosynthesis and elongation of fatty acids) was observed in D2. FAS had the highest relative expression in D1 and the lowest in D3 and D5 where both included 50 % linseed oil and 50 % alternative oil. Regarding the antioxidant properties, replacement of fish oil with linseed oil (D2) increased the expression of CAT and GST significantly. Conclusively, the algae oil can be used as an alternative source of oil to enhance the growth and increase the deposition of EPA and DHA in in the selected strain of rainbow trout fillet for more sustainable and healthy seafood.