Effects of dietary Saccharomyces cerevisiae culture or live cells with Bacillus amyloliquefaciens spores on growth performance, gut mucosal morphology, hsp70 gene expression, and disease resistance of juvenile common carp (Cyprinus carpio)

A feeding experiment was conducted to examine the effects of dietary administration of brewer's yeast Saccharomyces cerevisiae culture or live cells with Bacillus amyloliquefaciens spores on the growth performance, gut mucosal morphology, general welfare, and disease resistance of juvenile common carp (Cyprinus carpio). Four practical diets were formulated, i.e. control diet, diet Y1 (supplemented with 1g/kg Saccharoculture, a Korean-made S. cerevisiae culture product containing 107CFU/g B. amyloliquefaciens spores), diet Y2 (supplemented with 2g/kg S. cerevisiae culture, DVAQUA®, produced by Diamond V Mills Inc., IA, USA, as the positive control) and diet Y3 (supplemented with Changlijian, a local product with each gram containing 1010CFU live S. cerevisiae cells and 1.2×1010CFU B. amyloliquefaciens spores, at the recommended dose of 0.2g product per kg feed). Each diet was randomly assigned to triplicate groups of 12 fish. The experiment was conducted in aquaria for 8weeks. Results showed that the growth performances were not significantly improved in all treatment groups. Intestinal mucosal morphology analysis indicated that the posterior intestinal microvillus length in treatments Y1 and Y2 was significantly increased compared to control (P<0.05), while significantly reduced posterior intestinal microvillus density was observed in Y3 (P<0.05). The expression of the gene involved in animal welfare (70kDa-Heat Shock Protein gene) was analyzed. No significant difference in hsp70 gene expression was observed in the intestine for different dietary groups. In the liver, the expression was decreased in Y1 and Y2, while in Y3 the expression was significantly increased (P<0.05). However, the expression was significantly up-regulated in the kidney for Y2. Lastly, all treatment groups showed some trend of protection against A. hydrophila infection in common carp. In conclusion, lower level of S. cerevisiae culture with B. amyloliquefaciens spores (1g/kg Saccharoculture) may confer some beneficial effect to common carp, but the supplementation of live S. cerevisiae cells with B. amyloliquefaciens spores didn't provide any improvements under the present experimental conditions.