Abstract：Grass carp (Ctenopharyngodon idellus) with body weight of (110.23±0.43) g was reared in a covered net cage (3 m×2 m×1.2 m) at water temperature of 25—30 ℃ and fed diets containing Bacillus, Lactobacillus, and Saccharomyces probiotics (8.0×109 cfu/g) at a dose of 0% (control group), 0.5% and 2% for 60 days to investigate the effects of probiotics on the intestinal structure, flora and enzyme activities of grass carp. It was found that there were significant increase in weight gain rate and specific growth rate and significant decrease in ratio of viscera to body weight and food conversion ratio in the grass carp fed the diet containing 2% of probiotics (P<0.05). There were significantly increase in intestinal extension rate, midgut muscle layer thickness, and villus height and the activities of midgut amylase and lipase in the grass carp fed the diet containing 2% of probiotics (P<0.05). Increase in diversity, and abundance in intestinal flora and composition of intestinal microorganisms was observed in the grass carp fed the diets containing different proportions of probiotics. At the phylum level, the maximal contents of Clostridium (63.56%) and Firmicutes (32.52%) were found in grass carp in the control group, and the maximal contents of clostridium (61.82%) and firmicutes (20.27%) in the intestinal microorganisms in grass carp in the 0.5% group, with the maximal content of firmicutes(64.20%) in 2% group. At the genus level, the dominant bacteria in the intestinal tract of grass carp in the 2% group were directly changed, and the abundance of Paeniclostridium and Erysipelatoclostridium was increased significantly. The metabolic function of intestinal microorganisms was enhanced, and the abundance of bacteria related to the functions of inorganic ion transport and metabolism, carbohydrate transport and metabolism, and amino acid transport and metabolism was increased with the increase in the dose of the probiotics. It can be concluded that supplementation of probiotics composed of Bacillus, Lactobacillus and Saccharomyces in the feed can be an important measure to produce green feed for grass carp.
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2020, Vol. 39 
