In order to explore the effects of probiotics on the water quality, growth performance, nonspecific immunity, digestion, and intestinal flora of Macrobrachium rosenbergii in the biofloc culture system, three groups (six replicates in each group) were set up and divided into no bacteria (control group, Con), Bacillus subtilis (BS), and effective microorganisms (EM) in the current experiment. After dissolution of the water, the carbon source (glucose) was evenly sprayed in the aquaculture tank to construct a biofloc with a C/N of 15. A total of 1260 giant freshwater prawn (Macrobrachium rosenbergii) with an initial body weight of (2.09 ± 0.03) g were randomly assigned to 18 tanks (70 per tank). BS group and EM group significantly reduced total nitrogen concentration. Both BS and EM groups significantly increased final mean body weight, weight gain, and specific growth rate, but significantly decreased feed conversion rate of Macrobrachium rosenbergii. BS group significantly increased plasma superoxide dismutase, lysozyme, and acid phosphatase contents, but significantly decreased plasma malonaldehyde content. EM group significantly increased serum acid phosphatase content and intestinal trypsin activity but significantly decreased the Chao and ACE index of species richness. BS group and EM group significantly decreased the abundance of Chloroflexi and Verrucomicrobiota. BS group significantly increased the abundance of Bacillus. Overall, adding probiotics affected water quality, Macrobrachium rosenbergii performance, and microbial community. The results showed that Bacillus subtilis is a good biofloc probiotic additive.

To investigate the effects of dietary tributyrin (TB) and alanyl-glutamine (AGn) on the intestinal health of largemouth bass (Micropterus salmoides) fed with high-level soybean meal (SM) diet, six isonitrogenous (41.36%) and isolipidic (10.25%) diets were formulated and fed to largemouth bass (initial body weight 25.5 ± 0.5g) for 8 weeks. The two control diets contained 34.8% peanut meal (PM) and 41.3% SM, while the other four experimental diets supplemented TB at 0.1% (TB0.1), 0.2% (TB0.2) and AGn at 1% (AGn1), 2% (AGn2) in SM, respectively. The results showed that there were no significant differences in weight gain, survival rate, and hepatosomatic index among all groups (P>0.05), while feed coefficient rate in AGn1, AGn2 and TB0.2 groups was significantly lower than that in SM group (P< 0.05). Compared with the PM group, the intestinal inflammation of largemouth bass in SM group were obvious, accompanied by the damage of intestinal structure, the decrease of digestive enzyme activity, and the up-regulation of proinflammatory cytokines. Compared with the SM group, the activities of intestinal trypsin, lipase and foregut amylase in TB and AGn groups increased significantly (P<0.05), and the gene expression levels of acetyl-CoA carboxylase (ACC), caspase-3, caspase-8, caspase-9, tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β) were down-regulated, while the gene expression levels of target of rapamycin (TOR) and eIF4E-binding protein (4E-BP) were up-regulated in all experimental groups (P<0.05). It can be concluded that supplementation of 1%-2% AGn and 0.1%-0.2% TB can alleviate enteritis caused by high-level soybean meal, and the recommend level is 2% AGn and 0.2% TB.