Torula Yeast in the Diet of Atlantic Salmon Salmo Salar and the Impact on Growth Performance and Gut Microbiome.

Abstract

BackgroundLarge scale Atlantic salmon (Salmo salar) aquaculture is expanding, and with it, the need to find suitable replacements of conventional protein sources used in formulated feeds. Torula yeast (Cyberlindnera jadinii) has been identified as a promising alternative protein for aquaculture feeds, and can be sustainable cultivated from lignocellulosic biomasses, contributing to circular economic growth. The present study aimed to investigate the impact of torula yeast on the growth performance and the gut microbiome of freshwater Atlantic salmon to facilitate the commercial uptake of this alternative protein. Two types of diets were assessed in this study. Firstly, a marine protein base diet where fish meal (FM) was replaced with increasing inclusion levels of torula yeast, (0%, 10%, 20%) to provide a simplified replacement. Secondly, a marine protein and plant protein combination where mixed plant meals (MIX) were replaced with increasing inclusion levels of torula yeast, (0%, 10%, 20%) to provide a commercial relevant dietary replacement.ResultsThis study demonstrated that 20% torula yeast can replace fish meal without alteration to the growth performance while leading to potential benefits for the gut microbiome by increasing the presence of bacteria positively associated with the host. However, when torula yeast replaced a mix of plant meal in a combined protein source diet results suggest 10% inclusion of yeast produced the best growth performance results compared with both the control and 20% inclusion. At the highest inclusion level for the mixed diets potentially negative changes were observed in the gut microbial community, such as a decrease in lactic acid bacteria and an increased level of bacteria associated with slower growth in other salmonid species.ConclusionsThis study supports the application of torula yeast in the diet of Atlantic salmon as a partial replacement for conventional protein sources. However, the other components of the diet will need to be considered to determine the optimal inclusion level for this alternative protein. Future research should further optimise the inclusion of torula yeast in salmonid diets and investigate its influence on the functional role of the fish gut microbiome to facilitate improved formulated feed formulations and ensure a sustainable development of the aquaculture industry.