Effects of brewer’s spent yeast dietary inclusion on growth performance, intestinal histology, body composition, and immunity-related genes expression in Salmo salar parr

Increasing global demand for seafood and declining wild fish stocks highlight the need for sustainable protein alternatives in aquafeed formulation, particularly for high-value species such as salmonids. Brewer’s spent yeast (BSY), a nutritious food industry by-product, represents a promising resource to improve aquafeed sustainability. A 9-week feeding trial was conducted in a freshwater recirculating aquaculture system to evaluate dietary BSY replacing 3%, 6%, 9%, and 12% of total crude protein in diets for Atlantic salmon (Salmo salar; 5.00 ± 0.08 g). Diets with 6% BSY yielded the highest weight gain (21.39 g) and specific growth rate (1.81). Histological analysis showed that inclusion levels up to 12% did not induce pro-inflammatory responses or detrimentally alter intestinal morphology; variations in vilus height and goblet cell counts lacked statistical significance. The upregulation of nuclear factor kappa B (nfκb) and inhibitor of NFκB (iκbα) at 9% inclusion suggests a potential immunomodulatory response, but no effects on gut integrity were apparent. To summarize, a 6% BSY protein inclusion promotes growth rate, causes non-significant changes in body protein and fat, induces only a restricted upregulation of il-1β, and maintains normal intestinal histology. Therefore, moderate BSY inclusion may serve as a functional protein supplement in salmon feeds.