The effects of fish oil replacement by vegetable oils on growth performance and fatty acid profile of rainbow trout: Re-feeding with fish oil finishing diet improved the fatty acid composition

The present study aimed to demonstrate the effects of feeding vegetable oil (VO)-based diets and their blends on growth, feed utilization and fatty acid (FA) profile in rainbow trout, Oncorhynchus mykiss. Juveniles were fed five experimental diets in which dietary fish oil (FO diet containing anchovy oil) was totally or partially replaced by cottonseed oil (CSO), canola oil (CO), MIX1 (50% FO, 25% CSO and 25% CO) and MIX2 (50% CSO and 50% CO) in a grow-out period for 12 weeks. Afterwards, all fish were switched to a diet containing 100% FO diet for a further 12 weeks to determine the progressive recovery of fatty acid (FA) profile of rainbow trout. Results showed that total and/or partial replacement of FO did not negatively affect growth and feed utilization. Feeding VOs significantly reduced body contents of arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) to a lower degree than their reduction in the diet. Re-feeding with FO-diet for 12 weeks led to significant (P < 0.05) improvements in highly unsaturated fatty acid (HUFA), with a full recovery in ARA contents of rainbow trout. Finally, FA profile in whole body of MIX1 fed fish had the closest resemblance to that of FO fed fish.