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

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  < 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  < 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.