Torula yeast in the diet of Atlantic salmon Salmo salar and the impact on growth performance and gut microbiome

Abstract

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.

Alternative Proteins for Fish Diets: Implications beyond Growth

“…The replacement of 20% of fishmeal with a mixture of yeasts (corresponding to 10% inclusion) in rainbow trout diets had no deleterious effect on gut microbial diversity and composition [105]. In agreement, including up to 10% torula yeast (Cyberlindnera jadinii) biomass to replace fishmeal in freshwater Atlantic salmon diets did not affect gut microbial diversity [106]. However, the 20% inclusion of this yeast in a plant protein-based diet reduced growth performance, in association with a reduction in microbial diversity; overall, a higher protein replacement with yeast biomass led to a reduction of LAB abundance in the gut.…”

Impact of Putative Probiotics on Growth, Behavior, and the Gut Microbiome of Farmed Arctic Char (Salvelinus alpinus)

“…Probiotic treatment did not affect the relative abundance of the three dominant taxa in this study, with the exception of C. maltaromaticum SF1944 which was associated with a significantly reduced relative abundance of the Brevinema sp., possibly due to competition for the same niche. Brevinema , as well as Staphylococcus and Bacillus , the other two taxa with a significant reduction in abundance after probiotic treatment, have all been previously detected in farmed fish gut microbiomes, sometimes representing over a quarter of the relative community abundance ( Parata et al, 2020 ; Skrodenytė-Arbačiauskienė et al, 2021 ; Leeper et al, 2022 ) and therefore likely benign to the host organism.…”

“…DNA was extracted from defrosted fish guts as previously described in Leeper et al (2022) using the QIAamp PowerFecal Pro DNA Kit (Qiagen) with modifications. Two negative extraction control samples containing only zirconia/silica beads and CD1 buffer were included and processed alongside the other samples.…”

Fish disease and intestinal microbiota: A close and indivisible relationship

“…16 There are also reports on the participation of certain bacteria and yeasts in the degradation of nonnaturally metabolized nutrients by the fish gut, improving nutrient availability and absorption and, consequently, fish growth. 17,18 Furthermore, some gut microbiota bacteria can produce the amounts of vitamin B 12 required by the fish. 19 The biological importance of the microbiota is currently beyond doubt, but there is evidence that diseases represent one of the most influential factors affecting its function and resilience.…”

“…One pioneering work reported the zebrafish gut microbiota modulating the expression of 212 genes associated with nutrient metabolism, innate immune response and epithelial proliferation 16 . There are also reports on the participation of certain bacteria and yeasts in the degradation of non‐naturally metabolized nutrients by the fish gut, improving nutrient availability and absorption and, consequently, fish growth 17,18 . Furthermore, some gut microbiota bacteria can produce the amounts of vitamin B 12 required by the fish 19 …”