The synergistic effects of the probiotic (Lactobacillus fermentum) and cinnamon, Cinnamomum sp. powder on growth performance, intestinal microbiota, immunity, antioxidant defence and resistance to Yersinia ruckeri infection in the rainbow trout (Oncorhynchus mykiss) under high rearing density

The present study was conducted to examine the potential effects of two dietary supplements, the probiotic, Lactobacillus fermentum (LB) (1 × 108 CFU/ml) and 0.5% cinnamon powder (CP) alone and in combination form [LB (1 × 108 CFU/ml) + CP (0.5%)] on growth, intestinal microbiota, immune and antioxidant system and resistance to Yersinia ruckeri infection in the rainbow trout, Oncorhynchus mykiss under high rearing density. Fish were fed experimental diets [control (T1): (non‐supplemented fish), T2: fish fed 1 × 108 CFU/ml L. fermentum, T3: fish fed 0.5% CP and T4: fish fed 1 × 108 CFU/ml L. fermentum + 0.5% CP] for 60 days. After the feeding period, the growth performance, intestinal microbiota, immunity and antioxidant defence were assayed and fish challenged with Y. ruckeri. The supplements alone or in combination showed higher final weight, weight gain and lower feed conversion ratio compared with control. However, the specific growth rate and protein efficiency ratio improved when the supplements were used in combination. The supplementation of fish with L. fermentum alone and in combination with CP increased the activity of protease and amylase (p