| Summary: | The aim of the present study was to investigate the effect of microalgae, Chlorella vulgaris, and brewer’s yeast, Saccharomyces cerevisiae, on growth performance, digestive enzymes activity and intestinal microbiota in juvenile sterlet, Acipenser ruthenus. Total numbers of 315 juveniles (24.5 ± 0.2 g) were divided into 7 treatments and were fed with a basal diet containing different amounts of Chlorella and yeast during 8 weeks. Treatments 1 to 7 were fed with a basal included diet that not supplemented with Chlorella and yeast (control or T1); and supplemented with 1% yeast (T2); 0.5% yeast (T3); 3% Chlorella (T4); 5% Chlorella (T5); a combination of 0.5% yeast and 5% Chlorella (T6); and also a combination of 3% yeast and 1% Chlorella (T7), respectively. At the end of trial, growth indices, digestive enzymes and total number of intestinal bacteria were measured. The results showed that the addition of yeast and Chlorella (T6 and T7) to the fish diet enhanced growth performance, increased the secretion of digestive enzymes and also elevated the number of intestinal bacteria compared to the control (p<0.05). The best growth performance was observed in T5 (5% Chlorella), followed by T6 and T7 (combination of Chlorella and yeast). So that, the highest amount of body weight gain, average daily growth, specific growth rate, and the lowest feed conversion ratio were observed in T5, T6 and T7 (p<0.05). No significant difference was observed in the survival rate between treatments (p>0.05). The results showed that supplementing the diet of sterlet juveniles with microalgae and brewer’s yeast as well as with their combination significantly enhance the growth performance, secretion of digestive enzymes and intestinal bacterial flora.
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