The implications of substituting dietary fish oil with vegetable oils on the growth performance, fillet fatty acid profile and modulation of the fatty acid elongase, desaturase and oxidation activities of red hybrid tilapia, Oreochromis sp.

Abstract

A 75-day feeding trial was carried out to examine the effects of fish oil (FO) replacement with various alternative vegetable oil (VO) on the growth performance and feed utilization efficiency of red hybrid tilapia (Oreochromis sp.). The VO evaluated included canola oil (high in monoenes), perilla oil (high in n−3 polyunsaturated fatty acids, PUFA), sunflower oil (high in n−6 PUFA) and refined, bleached, deodorized palm olein (high in saturates) added as the sole lipid source in semi-purified experimental diets. The ability of hybrid tilapia to biosynthesize long chain-polyunsaturated fatty acids (LC-PUFA) from dietary 18:2n−6 and 18:3n−3 was also determined. With the exception of sunflower oil, results showed that total FO replacement by various VO did not compromise (P>0.05) tilapia growth performance. However, dietary VO significantly (P<0.05) influenced the fatty acid composition of tilapia fillet and whole-body lipids through changes in the overall fatty acid metabolism. The total Δ5 and Δ6 fatty acid desaturase activities were exclusively triggered in tilapia fed VO-based diets. Tilapia fed the VO diets, which contained no PUFA longer than C18, recorded significant amounts of both n−6 and n−3 LC-PUFA in their tissue lipids. Dietary canola oil (CO) increased Δ-6 desaturation of 18:3n−3 to the greatest extent despite the dietary 18:3n−3 content being comparatively lower than dietary perilla oil (PeO). Beta-oxidation of 18:3n−3 was observed to be highest in fish fed the PeO diet, indicating that the 18:3n−3 content in the PeO diet exceeded the optimum substrate level for Δ-6 desaturase. Omega-3 LC-PUFA biosynthetic activities were highest in fish fed the CO diet and resulted in a comparatively higher eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) content than in fish fed other VO diets. However, endogenous LC-PUFA synthesis induced by the VO diets was insufficient to rival the n−3 LC-PUFA content of fish fed the FO diet. It was also observed that β-oxidation of 18:3n−3 and 18:2n−6 was regulated by tissue n−3/n−6 PUFA ratio and proportional to their dietary level. This study provided the first comprehensive evidence of the significant impact of dietary oils with different fatty acid class profile on the in vivo fatty acid metabolism of tilapia. Statement of relevanceMarine fish oil (FO) was traditionally used as the major lipid source in commercial tilapia feeds to provide energy and essential fatty acids as well as to impart palability to the feed. With the rising costs of FO and limited global supplies, the use of alternative lipid resources in aquafeeds, including tilapia feeds, has become more critical to enable the continued sustainability and scalability of the global aquaculture industry. Terrestrial vegetable oil (VO) are viable alternatives since their production is more sustainable and cost-effective. However, unlike FO, which is rich in n−3 long chain-polyunsaturated fatty acids (LC-PUFA), VO are deficient in these essential fatty acids and but high in other fatty acid classes. The present study evaluated perilla oil (high levels of n−3 polyunsaturated fatty acids), sunflower oil (rich in n−6 PUFA), canola oil (high amounts of monounsaturated fatty acids) and palm oil (rich in saturated fatty acids) together with fish oil. By understanding how dietary lipid source with different major fatty acid classes modulates in vivo fatty acid metabolism, we can better formulate fish feeds that can optimize not only growth performance but also maintaining the health benefits of eating seafood for the human consumer in regards to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels in farmed fish fillets. As far as we know, there is currently no information comparing the fatty acid metabolism of red hybrid tilapia fed diets with lipids containing different major fatty acid classes.