Atlantic salmon aquaculture is expanding, and with it, the need to find suitable replacements for conventional protein sources used in formulated feeds. Torula yeast (Cyberlindnera jadinii), has been identified as a promising alternative protein for feed and can be sustainably cultivated on lignocellulosic biomasses. The present study investigated the impact of torula yeast on the growth performance and gut microbiome of freshwater Atlantic salmon. A marine protein base diet and a mixed marine and plant protein base diet were tested, where conventional proteins were replaced with increasing inclusion levels of torula yeast, (0%, 10%, 20%). This study demonstrated that 20% torula yeast can replace fish meal without alteration to 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 plant meal in a mixed protein diet, results suggested that 10% inclusion of yeast produced the best growth performance results but at the 20% inclusion level of yeast, potentially negative changes were observed in the gut microbial community, such as a decrease in lactic acid bacteria. This study supports the continued investigation of torula yeast for Atlantic salmon as a partial replacement for conventional proteins.

Beneficial bacteria promise to promote the health and productivity of farmed fish species. However, the impact on host physiology is largely strain-dependent, and studies on Arctic char (Salvelinus alpinus), a commercially farmed salmonid species, are lacking. In this study, 10 candidate probiotic strains were subjected to in vitro assays, small-scale growth trials, and behavioral analysis with juvenile Arctic char to examine the impact of probiotic supplementation on fish growth, behavior and the gut microbiome. Most strains showed high tolerance to gastric juice and fish bile acid, as well as high auto-aggregation activity, which are important probiotic characteristics. However, they neither markedly altered the core gut microbiome, which was dominated by three bacterial species, nor detectably colonized the gut environment after the 4-week probiotic treatment. Despite a lack of long-term colonization, the presence of the bacterial strains showed either beneficial or detrimental effects on the host through growth rate enhancement or reduction, as well as changes in fish motility under confinement. This study offers insights into the effect of bacterial strains on a salmonid host and highlights three strains, Carnobacterium divergens V41, Pediococcus acidilactici ASG16, and Lactiplantibacillus plantarum ISCAR-07436, for future research into growth promotion of salmonid fish through probiotic supplementation.

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.

Atlantic salmon aquaculture is expanding, and with it, the need to find suitable replacements for conventional protein sources used in formulated feeds. Torula yeast (Cyberlindnera jadinii), has been identified as a promising alternative protein for feeds and can be sustainably cultivated from lignocellulosic biomasses. The present study investigates the impact of torula yeast on the growth performance and the gut microbiome of freshwater Atlantic salmon. Both a marine protein base diet and a mixed marine and plant protein base diet were tested, where conventional proteins were replaced with increasing inclusion levels of torula yeast, (0%, 10%, 20%). This study demonstrated that 20% torula yeast can replace fish meal without alteration to 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 plant meal in a mixed protein diet, results suggest 10% inclusion of yeast produced the best growth performance results and at the highest inclusion level, potentially negative changes were observed in the gut microbial community, such as a decrease in lactic acid bacteria. This study supports the continued investigation of torula yeast for Atlantic salmon as a partial replacement for conventional proteins.