Genetically improved farmed Nile tilapia and red hybrid tilapia showed differences in fatty acid metabolism when fed diets with added fish oil or a vegetable oil blend

A 2 × 2 factorial 14-week feeding trial was conducted to evaluate the fatty acid metabolism in two different tilapia genotypes [Nile tilapia (Oreochromis niloticus, GIFT strain) and red hybrid tilapia (Oreochromis sp.)] fed a fish oil (FO)- or blended vegetable oil (BVO)-based semipurified diet. The BVO was formulated using olive oil (15%), sunflower oil (15%), linseed oil (30%) and refined, bleached, deodorized palm olein (40%) to mimic the major fatty acid classes of FO. In general, no significant effect (P > 0.05) of tilapia genotype or lipid source on fatty acid digestibility was observed. The fatty acid composition of tilapia whole-body, irrespective of genotype, was significantly (P < 0.05) affected by the dietary lipid source, but interestingly, tilapia fed the BVO diet which contained no polyunsaturated fatty acids (PUFA) longer than C18, recorded significant amounts of both n-6 and n-3 long chain (LC)-PUFA. The present study clearly indicated that tilapia farming can be a net producer of n-3 LC-PUFA. Using the whole-body fatty acid balance method, total fatty acid β-oxidation, Δ-5 and Δ-6 desaturation were observed to be significantly higher in fish fed the BVO diet compared to fish on the FO diet. No apparent Δ-5 desaturase activity on n-3 PUFA was observed in fish fed the FO diet. Both dietary lipid source and tilapia genotype elicited significant effects on the elongase activity on 18:4n-3, 18:2n-6 and 18:3n-6. Tilapia fed the BVO diet exhibited efficient bioconversion of 18:2n-6 to n-6 LC-PUFA indicating that the fatty acid metabolism of tilapia is able to fully compensate for the lack of dietary n-6 LC-PUFA when fed a vegetable oil-based diet. All fish showed active liponeogenesis suggesting that the addition of higher dietary levels of SFA and MUFA may be beneficial to tilapia. Irrespective of diet, GIFT tilapia showed higher rates of fatty acid neogenesis along with higher rates of elongation, Δ-5 and Δ-6 desaturation of both the n-6 PUFA and n-3 PUFA. The farming of improved strains of Nile tilapia may rely less heavily on marine-derived raw materials for aquafeed production.