Two trials were performed to determine digestibility coefficients for torula yeast in Rainbow trout (Oncorhynchus mykiss) and its performance in plant-based or fishmeal-based diets, respectively. For the digestibility trial, six groups of 15 rainbow trout (mean body mass 100 ± 10 g) were placed in 60 L cylindro-conical tanks supplied with well aerated water at a regulated flow rate of 4 L/min. Fish were hand fed one of the 2 diets (Control diet or torula yeast diet) containing Y2O3 (inert marker), twice a day to visual satiation. The torula yeast diet contained 75% of the control diet and 25% torula yeast. The dry matter, protein, energy, and ash apparent digestibility coefficients were 78.6%, 93.8%, 84.8%, and 48.7%, respectively. For the growth trial, Rainbow trout of approximately 44 g initial body weight were distributed into 15 tanks (30 fish per 300-liter tank) and fed a commercial diet twice a day during 10 days for acclimatization to rearing conditions. After this period, the growth trial started, and fish were fed twice a day until apparent satiation with one of the 5 experimental diets. The experiment included three tanks per diet. The total duration of the growth trial was 12 weeks. The diets included a 20% fishmeal reference diet (FM) and a plant-based only reference diet (PB), test diets included 10% torula yeast inclusion replacing either fishmeal (FM SY10) or plant proteins (PB SY10), and a 20% torula yeast inclusion replacing all fishmeal (PB SY20). The plant-based only diets had significantly lower specific growth rate, feed conversion ratio, and daily feed intake compared with the other four diets. No significant differences were observed for hepatosomatic index and viscerosomatic index across treatments. No statistical differences were observed relating to growth performance between any diet containing torula yeast and the fishmeal reference diet. Results indicate that torula yeast is suitable for the replacement of fishmeal in the diets of Rainbow trout in terms of nutrient digestibility and growth performance. Better performance was observed in plant-based diets devoid of fishmeal when torula yeast was included.