Balancing dietary plant-based lipids and cholesterol to increase fillet omega-3 deposition in rainbow trout (Oncorhynchus mykiss) fed a diet without animal ingredients

Abstract

We hypothesized that a low phytosterol oil, such as soybean oil, in combination with an α-linolenic acid (ALA) rich oil, such as linseed oil, and supplemental cholesterol could effectively replace fish oil in salmonid feeds. As such, the primary objective was to blend soybean oil with linseed oil and supplemental cholesterol to maintain fish growth and increase de novo production of the omega-3 fatty acids (n-3 FA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in trout muscle, since EPA and DHA have been identified as beneficial nutrients in human nutrition, and farmed seafood must meet consumer needs and expectations. To accomplish this, we used soy oil for its low phytosterol properties in combination with linseed oil for its n-3 FA content, with and without cholesterol to improve utilization. Upon conclusion of the study, our results did not support our hypothesis. Trout fed plant-based diets containing any amount of soy oil had reduced growth performance. Only fish fed the plant-based diet with 100% linseed oil plus supplemental cholesterol grew as well as both control groups, fishmeal/fish oil and plant meal/fish oil. Dietary cholesterol supplementation increased plasma cholesterol levels and EPA in fillets (P < 0.05). Two-way ANOVA demonstrated that growth performance and muscle EPA content were significantly increased in fish fed cholesterol-supplemented diets. However, expression of genes involved in fatty acid biosynthesis were not enhanced by cholesterol, suggesting a potential disconnect between gene expression and functional activity. Although our hypothesis failed and soybean oil was found to be less accepted by the fish, resulting in lower growth and feed intake, we were successful in developing a high soy-protein diet (35%) with all-plant ingredients using linseed oil and supplemental cholesterol that resulted in equal fish performance to fish fed a fishmeal/fish oil control diet. More research is needed to identify a cost-effective EPA/DHA source to meet consumer needs and expectations for n-3 FA in trout fillets.