Abstract
The present study was conducted to examine the potential effects of two dietary supplements, the probiotic, Lactobacillus fermentum (LB) (1 x 10(8) CFU/ml) and 0.5% cinnamon powder (CP) alone and in combination form [LB (1 x 10(8) 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 x 10(8) CFU/ml L. fermentum, T3: fish fed 0.5% CP and T4: fish fed 1 x 10(8) 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 < 0.05). Although the supplementation of fish with the L. fermentum alone or in combination with CP enhanced immune and antioxidant defence components in serum and mucus, this effect was more pronounced when fish fed L. fermentum + CP. The L. fermentum alone or in combination with CP reduced the fish stress, as the concentrations of glucose and cortisol decreased in these treatments. Alkaline phosphatase activity in blood in fish fed CP and those fed L. fermentum + CP and lactate dehydrogenase activity in fish fed L. fermentum + CP decreased compared with control. Furthermore, fish supplemented with L. fermentum + CP significantly increased resistance to Y. ruckeri infection (p < 0.05). In conclusion, the findings of the present study indicated that a combination of CP and L. fermentum in the diet can be more effective in improving growth, immunity, digestive enzyme performance and resistance to Y. ruckeri infection in rainbow trout, suggesting a synergistic effect for them.