Impact of Brewer’s Spent Yeast Supplemented Diets on the Growth Rates and Intestinal Bacterial Communities of Farmed Rainbow Trout ( <i>Oncorhynchus mykiss</i> )

Brewery byproducts such as brewer’s spent yeast (BSY, Saccharomyces cerevisiae ) have little‐to‐no commercial value; however, BSY contains nutritional properties with the potential to be utilized as a beneficial feed additive by the aquaculture industry. It was hypothesized that BSY could be used as a supplement in farmed rainbow trout ( Oncorhynchus mykiss ) diets to improve production and health in relation to the gastrointestinal (GI) bacterial community. Fourteen juvenile rainbow trout (28.6 ± 0.4 g, mean ± standard error [SEM]) were stocked per 12 polyethylene tanks (170 L each) in a single recirculating aquaculture system (RAS). Three treatment groups, performed in quadruplicate at the tank level, included a control (commercial feed), low yeast (LY, commercial feed coated with 2% BSY), and high yeast (HY, commercial feed coated with 5% BSY). Over the 8‐week trial, compared to the control, the LY and HY fed fish grew significantly ( p &lt; 0.01) faster, with a 20.8% and 35.4% increase in weight gain, respectively. No differences were observed for fish biometrics or bacterial communities between treatment groups. However, between tissue types significant differences ( p &lt; 0.05) in the bacterial communities were observed for alpha diversity. Overall, supplemented BSY served as an effective growth additive for rainbow trout without negatively impacting animal health.