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.

A bioflocculant-producing bacterium,Bacillus megateriumSP1, was isolated from biofloc in pond water and identified by using both 16S rDNA sequencing analysis and a Biolog GEN III MicroStation System. The optimal carbon and nitrogen sources forBacillus megateriumSP1 were 20 g L⁻¹of glucose and 0.5 g L⁻¹of beef extract at 30°C and pH 7. The bioflocculant produced by strain SP1 under optimal culture conditions was applied into aquaculture wastewater treatment. The removal rates of chemical oxygen demand (COD), total ammonia nitrogen (TAN), and suspended solids (SS) in aquaculture wastewater reached 64, 63.61, and 83.8%, respectively. The volume of biofloc (FV) increased from 4.93 to 25.97 mL L⁻¹. The addition ofBacillus megateriumSP1 in aquaculture wastewater could effectively improve aquaculture water quality, promote the formation of biofloc, and then form an efficient and healthy aquaculture model based on biofloc technology.