The conversion of nonedible biomass to protein for use in feed is an attractive strategy toward improved sustainability in aquaculture. We have studied the possibility to produce protein-rich yeast Candida utilis on a medium consisting of enzymatically hydrolyzed sulphite-pulped spruce wood, mainly providing glucose, and enzymatically hydrolyzed brown seaweed, supplemented with ammonium sulfate. The results show that this blend constitutes a complete fermentation medium that enables good growth rates and cell yields. Results from a salmon feeding trial showed that the yeast can replace parts of a traditional fishmeal diet without harmful effects, although the apparent protein digestibility coefficient for the yeast was suboptimal. While further optimization of both the fermentation process and downstream processing is needed, the present proof-of-concept study shows a path to the production of microbial protein based on a simple, local and sustainable fermentation medium.